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Hindu calendar is a collective name for most of the lunisolar calendars and solar calendars used in India since ancient times. Since ancient times it has undergone many changes in the process of regionalization and today there are several regional Indian Hindu calendars. It has also been standardized as Indian national calendar. Nepali calendar, Assamese Calendar, Bengali calendar, Malayalam calendar, Tamil calendar, Telugu calendar, Kannada calendar etc. are some prominent regional Hindu calendars. The common feature of all regional Hindu calendars is that the names of the twelve months are the same (because the names are based in Sanskrit) though the spelling and pronunciation have come to vary slightly from region to region over thousands of years. The month which starts the year also varies from region to region. The Buddhist calendar and the traditional lunisolar calendars of Cambodia, Laos, Myanmar, Sri Lanka and Thailand are also based on an older version of the Hindu calendar.
Most of the Hindu calendars are inherited from a system first enunciated in Vedāṅga Jyotiṣa's of Lagadha, a late BCE adjunct to the Veda-s, standardized in the Sūrya Siddhānta (3rd century CE) and subsequently reformed by astronomers such as Āryabhaṭṭa (499 CE), Varāhamihira (6th century CE), and Bhāskara II (12th century CE). Differences and regional variations abound in these computations, but the following is a general overview of Hindu lunisolar calendar.
In the Hindu calendar, the day starts with local sunrise. It is allotted five "properties" or "limbs", called aṅga-s. They are:
- the Tithi (one of 30 divisions of a synodic month) active at sunrise
- the Vāsara (ancient nomeclature), vāra (modern nomeclature), like in ravi-vāra, somā-vāra, etc. or weekday
- the Nakṣatra (one of 27 divisions of the celestial ecliptic) in which the moon resides at sunrise
- the Yoga (one of 27 divisions based on the ecliptic longitude of the sun and moon) active at sunrise time
- the Karaṇa (divisions based on tithis) active at sunrise.
Together 5 limbs or properties are labelled under as the pañcāṅga-s (Sanskrit: pañca = five). An explanation of the terms follows.
Vāsara refers to the weekdays and the names of the week in many western cultures bear striking similarities with the Vāsara:
|No.||Sanskrit name of the day
(Day begins at sunrise)
|Kannada name||Tamil name||English & Latin names of the approximate day
(Day begins at 00:00Hrs)
|Sunday/dies Solis||Ravi = Sun|
|Monday/dies Lunae||Soma = Moon|
|Tuesday/dies Martis||Maṅgala = Mars|
|Wednesday/dies Mercurii||Budha = Mercury|
|Thursday/dies Iovis||Deva-Guru Bṛhaspati = Jupiter|
|Friday/dies Veneris||Śukra = Venus|
|Sani <br||Saturday/dies Saturnis||Śani = Saturn|
The term -vāsara is often realized as vāra or vaar in Sanskrit-derived languages. There are many variations of the names in the regional languages, mostly using alternate names of the celestial bodies involved.
The ecliptic is divided into 27 Nakṣatra-s, which are variously called lunar houses or asterisms. These reflect the moon's cycle against the fixed stars, 27 days and 7¾ hours, the fractional part being compensated by an intercalary 28th nakṣatra titled Abhijit. Nakṣatra's computation appears to have been well known at the time of the Ṛgveda (2nd–1st millennium BCE).
The ecliptic is divided into the nakṣatras eastwards starting from a reference point which is traditionally a point on the ecliptic directly opposite the star Spica called Citrā in Sanskrit. (Other slightly different definitions exist.) It is called Meṣādi - "start of Aries"; this is when the equinox — where the ecliptic meets the equator — was in Aries (today it is in Pisces, 28 degrees before Aries starts). The difference between Meṣādi and the present equinox is known as Ayanāṃśa - denoting by how much of a fraction of degrees & minutes the ecliptic has progressed from its fixed (sidereal) position. Given the 25,800 year cycle for the precession of the equinoxes, the equinox was directly opposite Spica in 285 CE, around the date of the Sūrya Siddhānta.
The nakṣatra-s with their corresponding regions of sky are given below, following Basham. As always, there are many versions with minor differences. The names on the right-hand column give roughly the correspondence of the nakṣatra-s to modern names of stars. Note that nakṣatras are (in this context) not just single stars but are segments on the ecliptic characterised by one or more stars. Hence there are more than one star mentioned for each nakṣatra.
|Western star name|
|β and γ Arietis|
|35, 39, and 41 Arietis|
|λ, φ Orionis|
|Ātira or Tiruvātira
|Castor and Pollux|
|γ, δ and θ Cancri|
आश्ळेषा / आश्लेषा
|δ, ε, η, ρ, and σ Hydrae|
|11||Pūrva or Pūrva Phalguṇī
పూర్వా ఫల్గుణి / పుబ్బ
|δ and θ Leonis|
|12||Uttara or Uttara Phalguṇī
ఉత్తర ఫల్గుణి / ఉత్తర
|α, β, γ, δ and ε Corvi|
|α, β, γ and ι Librae|
|β, δ and π Scorpionis|
|α, σ, and τ Scorpionis|
|ε, ζ, η, θ, ι, κ, λ, μ and ν Scorpionis|
|δ and ε Sagittarii|
|ζ and σ Sagittarii|
|α, β and γ Aquilae|
|23||Śraviṣṭhā or Dhaniṣṭha
श्रविष्ठा or धनिष्ठा
|α to δ Delphinus|
|24||Śatabhiṣak or Śatatārakā
शतभिषक् / शततारका
पूर्वभाद्रपदा / पूर्वप्रोष्ठपदा
|α and β Pegasi|
उत्तरभाद्रपदा / उत्तरप्रोष्ठपदा
|γ Pegasi and α Andromedae|
The Sanskrit word Yoga means "union", but in astronomical calculations it is used in the sense of "alignment". First one computes the angular distance along the ecliptic of each object, taking the ecliptic to start at Meṣa or Aries (Meṣādi, as defined above): this is called the longitude of that object. The longitude of the sun and the longitude of the moon are added, and normalized to a value ranging between 0° to 360° (if greater than 360, one subtracts 360). This sum is divided into 27 parts. Each part will now equal 800' (where ' is the symbol of the arcminute which means 1/60 of a degree). These parts are called the yogas. They are labeled:
Again, minor variations may exist. The yoga that is active during sunrise of a day is the prevailing yoga for the day.
A karaṇa is half of a tithi. To be precise, a karaṇas is the time required for the angular distance between the sun and the moon to increase in steps of 6° starting from 0°. (Compare with the definition of a tithi above.)
Since the tithis are 30 in number, and since 1 tithi = 2 karaṇa, therefore one would logically expect there to be 60 karaṇa-s. But there are only 11 such karaṇa which fill up those slots to accommodate for those '30 tithi'-s. There are actually 4 "fixed" (sthira) karaṇa-s and 7 "repeating" (cara) karaṇa.
The 4 "fixed" karaṇa-s are:
The 7 "repeating" karaṇa-s are:
- Vava or Bava
- Valava or Bālava
- Taitila or Taitula
- Gara or Garaja
- Viṣṭi (Bhadra)
- Now the first half of the 1st tithi (of Śukla Pakṣa) is always Kiṃtughna karaṇa. Hence this karaṇa' is "fixed".
- Next, the 7-repeating karaṇa-s repeat eight times to cover the next 56 half-tithis. Thus these are the "repeating" (cara) karaṇa-s.
- The 3 remaining half-tithi-s take the remaining "fixed" karaṇa-s in order. Thus these are also "fixed" (sthira).
- Thus one gets 60 karaṇa-s from those 11 preset karaṇa-s.
The karaṇa-s at sunrise of a particular day shall be the prevailing karaṇa-s for the whole day. Note. The day changes at every sunrise i.e. from Sunrise 1 to Sunrise 2 - is 1 Vedic day.
Months of the lunisolar calendar 
When a new moon occurs before sunrise on a day, that day is said to be the first day of the lunar month. So it is evident that the end of the lunar month will coincide with a new moon. A lunar month has 29 or 30 days (according to the movement of the moon).
The tithi at sunrise of a day is the only label of the day. There is no running day number from the first day to the last day of the month. This has some unique results, as explained below:
Sometimes two successive days have the same tithi. In such a case, the latter is called an adhika tithi where adhika means "extra". Sometimes, one tithi may never touch a sunrise, and hence no day will be labeled by that tithi. It is then said to be a Tithi Kṣaya where Kṣaya means "loss".
Month names 
There are 12 months in Hindu lunar Calendar:
- Chaitra (चैत्र) Meṣa (Aries)
- Vaiśākha (वैशाख) Vṛṣabha (Taurus)
- Jyaiṣṭha (ज्येष्ठ) Mithuna (Gemini)
- Āṣāḍha (आषाढ ) Karka (Cancer)
- Śrāvaṇa (श्रावण) Siṃha (Leo)
- Bhādrapada or Bhādra also Proṣṭhapada (भाद्रपद,भाद्र,प्रोष्ठपद) Kanyā (Virgo)
- Āśvina in,sometimes Aśvayuja ( आश्विन,अश्वयुज) Tula (Libra)
- Kārtika (कार्तिक) Vṛścika (Scorpio)
- Agrahāyaṇa or, Mārgaśīrṣa (मार्गशीर्ष,अग्रहायण) Dhanus (Sagittarius)
- Pauṣa (पौष) Makara (Capricorn)
- Māgha (माघ) Kumbha (Aquarius)
- Phālguna (फाल्गुन)Mīna (Pisces)
Determining which name a lunar month takes is somewhat indirect. It is based on the rāshi (Zodiac sign) into which the sun transits within a lunar month, i.e. before the new moon ending the month.
There are 12 rāśi names, there are twelve lunar month names. When the sun transits into the Meṣa rāśi in a lunar month, then the name of the lunar month is Caitra. When the sun transits into Vṛṣabha, then the lunar month is Vaiśākha. So on.
If the transits of the Sun through various constellations of the zodiac (Rāśi) are used, then we get Solar months, which do not shift with reference to the Gregorian calendar. The Solar months along with the corresponding Hindu seasons and Gregorian months are:
|Kannada name||Tamil name||Gregorian
|Sidereal Vedic Zodiac|
The Sanskrit grammatical derivation of the lunar month names Caitra etc., is: the (lunar) month which has its central full moon occurring at or near the Citrā nakṣatra is called Caitra. Another example is let's say when Pūrṇimā occurs in or near Viśākha nakṣatra, this in turn results to the initiation of the lunar month titled Vaiśākha Māsa.
Similarly, for the nakṣatra-s Viśākha, Jyeṣṭhā, (Pūrva) Āṣāḍhā, Śravaṇa, Bhādrapadā, Aśvinī (old name Aśvayuj), Kṛttikā, Mṛgaśiras, Puṣya, Meghā and (Pūrva/Uttara) Phalguṇī the names Vaiśākha etc. at pūrṇimā, the other Lunar names are derived subsequently.
The lunar months are split into two Pakṣas of 15 days. The waxing paksha is called Śukla Pakṣa, light half, and the waning paksha the Kṛṣṇa Pakṣa, dark half. There are two different systems for making the lunar calendar:
- Amāvāsyanta or mukhya mana system – a month begins with a new moon and ends at new moon, mostly followed in the southern states
- Pūrṇimānta or gauna mana system – a month begins with a full moon and ends at full moon, followed more in the North.
p.s. Pūrṇimānta is also known as Śuklānta Māsa. And this system is recommended by Varāhamihira.
Extra months (Adhika Māsa) 
When the sun does not at all transit into any rāśi but simply keeps moving within a rāśi in a lunar month (i.e. before a new moon), then that lunar month will be named according to the first upcoming transit. It will also take the epithet of adhika or "extra". For example, if a lunar month elapsed without a solar transit and the next transit is into Meṣa, then this month without transit is labeled Adhika Caitra Māsa. The next month will be labeled according to its transit as usual and will get the epithet nija ("original") or Śuddha ("unmixed"). In the animation above, Year 2 illustrates this concept with Bhadrapada repeating twice; the first time the Sun stays entirely within Simha rashi thus resulting in an Adhika Bhakradapada.
Extra Month, or adhika māsa (māsa = lunar month in this context) falls every 32.5 months. It is also known as puruśottama māsa, so as to give it a devotional name. Thus 12 Hindu mas (māsa) is equal to approximate 356 days, while solar year have 365 or 366 (in leap year) which create difference of 9 to 10 days, which is offset every 3rd year. No adhika māsa falls during Kārtika to Māgh.
Lost months (Kṣaya Māsa) 
If the sun transits into two rāshis within a lunar month, then the month will have to be labeled by both transits and will take the epithet kṣaya or "loss". There is considered to be a "loss" because in this case, there is only one month labeled by both transits. If the sun had transited into only one raashi in a lunar month as is usual, there would have been two separate months labeled by the two transits in question.
For example, if the sun transits into Meṣa and Vṛṣabha in a lunar month, then it will be called Caitra-Vaiśākha kṣaya-māsa. There will be no separate months labeled Caitra and Vaiśākha.
A Kṣaya-Māsa occurs very rarely. Known gaps between occurrence of Kṣaya-Māsas are 19 and 141 years. The last was in 1983. January 15 through February 12 were Pauṣa-Māgha kṣaya-māsa. February 13 onwards was (Adhika) Phālguna.
If there is no solar transit in one lunar month but there are two transits in the next lunar month,
- the first month will be labelled by the first transit of the second month and take the epithet Adhika and
- the next month will be labelled by both its transits as is usual for a Kṣaya-Māsa
This is a very very rare occurrence. The last was in 1315. October 8 to November 5 were Kārtika Adhika-Māsa. November 6 to December 5 were Kārtika-Mārgaśīrṣa Kṣaya-Māsa. December 6 onwards was Pauṣa.
Religious observances in case of extra and lost months 
Among normal months, adhika months, and kshaya months, the earlier are considered "better" for religious purposes. That means, if a festival should fall on the 10th tithi of the Āshvayuja month (this is called Vijayadashamī) and there are two Āśvayuja (Āśvina)' months caused by the existence of an adhika Āśvayuja, the first adhika month will not see the festival, and the festival will be observed only in the second nija month. However, if the second month is āshvayuja kshaya then the festival will be observed in the first adhika month itself.
When two months are rolled into one in the case of a kshaya māsa, the festivals of both months will also be rolled into this Kṣaya Māsa'. For example, the festival of Mahāshivarātri which is to be observed on the fourteenth tithi of the Māgha Kṛṣṇa-Pakṣa was, in 1983, observed on the corresponding tithi of Pauṣa-Māgha Kṣaya Kṛṣṇa-Pakṣa, since in that year, Pauṣa and Māgha were rolled into one, as mentioned above. When two months are rolled into one in the case of a Kṣaya Māsa, the festivals of both months will also be rolled into this kṣaya māsa.
Vaiṣṇava calendar 
|Month||Predominating Deity-name of month|
Year of the lunisolar calendar 
The new year day is the first day of the shukla paksha of Chaitra. In the case of adhika or kshaya months relating to Caitra, the aforementioned religious rules apply giving rise to the following results:
- If an adhika Chaitra is followed by a nija Chaitra, the new year starts with the nija Caitra.
- If an adhika Chaitra is followed by a Chaitra-Vaishākha kshaya, the new year starts with the adhika Caitra.
- If a Caitra-Vaiśākha Kṣaya occurs with no adhika Chaitra before it, then it starts the new year.
- If a Caitra-Phālguna Kṣaya' occurs, it starts the new year.
Another kind of lunisolar calendar 
There is another kind of lunisolar calendar which differs from the former in the way the months are named. When a full moon (instead of new moon) occurs before sunrise on a day, that day is said to be the first day of the lunar month. In this case, the end of the lunar month will coincide with a full moon. This is called the pūrṇimānta māna - full-moon-ending reckoning, as against the amānta māna - new-moon-ending reckoning used before.
This definition leads to a lot of complications:
- The first pakṣa of the month will fall on Kṛṣṇa-Pakṣa whilst the second will be Śukla-Pakṣa in Pūrṇimānta system.
- The new year is still on the first day of the Caitra Śukla-Pakṣa. The subsequentPakṣa-s will, for example, be -
|First Pakṣa||Ending (2nd) Pakṣa|
- Phālguna Māsa is the last Lunar month, with the last pakṣa of the year in this pūrṇimānta system being Phālguna Śukla-Pakṣa.
- The Śukla Pakṣa of a given month, say Caitra, comprises the same actual days in both systems, as can be deduces from a careful analysis of the rules. However, the Caitra Kṛṣṇa-Pakṣa-s defined by the 2 systems will be on different days, since the Caitra Kṛṣṇa-Pakṣa precedes the Caitra Śukla-Pakṣa in the pūrnimānta system but follows it in the amānta system.
- Though the regular months are defined by the full moon, the adhika and kṣaya lunar months are still defined by the new moon. That is, even if the pūrnimānta system is followed, adhika or kṣaya months will start with the first sunrise after the new moon, and end with the new moon.
- The adhika month will therefore get sandwiched between the 2pakṣa-s of the nija months. For example, a Śrāvaṇa Adhika Māsa will be inserted as follows:
- nija Śrāvaṇa Kṛṣṇa-Pakṣa
- adhika Śrāvaṇa Śukla-Pakṣa
- adhika Śrāvaṇa Kṛṣṇa-Pakṣa and
- nija Shrāvana Śukla-Pakṣa
after which Bhādrapada Kṛṣṇa-Pakṣa will follow subsequently as usual.
- If there is an adhika Caitra, then it will follow the (nija) Caitra Krṣṇa-Pakṣa at the end of the year. Only with the nija Caitra Śukla-Pakṣa will the new year start. The only exception is when it is followed by a kṣaya, and that will be mentioned later.
- The kṣaya month is more complicated. If in the amānta system there is a Pauṣa-Māgha Kṣaya Māsa, then in the pūrnimānta system there will be the following pakṣa-s:
- Pauṣa Kṛṣṇa-Pakṣa
- Pauṣa-Maagha kshaya Śukla-Pakṣa
- Māgha-Phālguna Kṣaya Kṛṣṇa-Pakṣa and a
- Phālguna Śukla-Pakṣa.
- The special Kṣaya case where an adhika māsa precedes a kshaya māsa gets even more convoluted. First, we should remember that the Āśvina Śukla-Pakṣa is the same in both the systems. After this come the following Pakṣa-s:
- nija Kārtika Kṛṣṇa-Pakṣa
- adhika Kārtika Śukla-Pakṣa
- adhika Kārtika Kṛṣṇa-Pakṣa
- Kārtika-Māgaśīrṣa Kṣaya Śukla-Pakṣa
- Māgaśīrsa-Pauṣa Kṣaya Kṛṣṇa-Pakṣa
- Pauṣa Śukla-Pakṣa
followed by the Māgha Kṛṣṇa-Pakṣa etc., as usual.
- The considerations for the new year are:
- If there is a Caitra-Vaiśākha Kṣaya Śukla-Pakṣa:
- if an adhika Caitra' precedes it, then the adhika Caitra Śukla-Pakṣa starts the new year
- if not, the Kṣaya Śukla-Pakṣa starts the new year
- If there is a Phālguna-Caitra Kṣaya Śukla-Pakṣa then it starts the new year
- If there is a Caitra-Vaiśākha Kṣaya Śukla-Pakṣa:
However, none of these above complications cause a change in the day of religious observances. Since only the name of the Kṛṣṇa-Pakṣa-s of the months will change in the two systems, festivals which fall on the Kṛṣṇa-Pakṣa will be defined by the appropriate changed name. That is, the Mahāśivarātri, defined in the amānta māna to be observed on the fourteenth of the Māgha krishna paksha will now (in the pūrnimānta māna) be defined by the Phālguna krishna paksha.
Correspondence of the lunisolar calendar to the solar calendar 
A lunisolar calendar is always a calendar based on the moon's celestial motion, which in a way keeps itself close to a solar calendar based on the sun's (apparent) celestial motion. That is, the lunisolar calendar's new year is to kept always close (within certain limits) to a solar calendar's new year.
Since the Hindu lunar month names are based on solar transits, and the month of Caitra will, as defined above, always be close to the solar month of Meṣa (Aries), the Hindu lunisolar calendar will always keep in track with the Hindu solar calendar.
The Hindu solar calendar by contrast starts on April 14–15 each year. This signifies the sun's "entry" into Mesha rashi and is celebrated as the New Year in Assam, Bengal, Odisha, Manipur, Kerala, Punjab, Tamil Nadu and Tripura. The first month of the year is called "Chitterai (சித்திரை" in Tamil, "Medam" in Malayalam and Bohag in Assamese, Baisakh in Bengali/Punjabi and Nepali. This solar new year is celebrated on the same day in Myanmar, Cambodia, Laos, Nepal and Thailand due to Tamil influence on those countries.
Year numbering 
The epoch (starting point or first day of the zeroth year) of the current era of Hindu calendar (both solar and lunisolar) is February 18, 3102 BCE in the proleptic Julian calendar or January 23, 3102 BCE in the proleptic Gregorian calendar. According to the Purāṇa-s this was the moment when Śrī Kṛṣṇa returned to his eternal abode. Both the solar and lunisolar calendars started on this date. After that, each year is labeled by the number of years elapsed since the epoch.
This is an unusual feature of the Hindu calendar. Most systems use the current ordinal number of the year as the year label. But just as a person's true age is measured by the number of years that have elapsed starting from the date of the person's birth, the Hindu calendar measures the number of years elapsed. As of May 18, 2010[update], 5119 years have elapsed in the Hindu calendar. However, the lunisolar calendar year usually starts earlier than the solar calendar year, so the exact year will not begin on the same day every year.
Year names 
Apart from the numbering system outlined above, there is also a cycle of 60 calendar year names, called Samvatsaras, which started at the first year (at elapsed years zero) and runs continuously:
This system contains the concept of leap year also.Every 4th year will have 366 days and the others only 365.The starting point is Meshadi or Mesha Sankranti, ( 1st of the month Meṣa or the hindu solar new year).It is also calculated a day by day mode.beginning from 1 presently it runs 1864000+.... days.This means these much days have passed in the present Kaliyuga (1/10 of Catur-Yuga's total)
Hinduism follows Hindu units of time containing 4 eras (Technically Yuga) or ages, of which we are currently in the last. The four yugas are:
They are often translated into English as the golden, silver, bronze and Iron Ages. (Yuga means era or age.) The ages see a gradual decline of dharma, wisdom, knowledge, intellectual capability, life span and emotional and physical strength. The epoch provided above is the start of the Kali Yuga. The Kali Yuga is 432,000 years long. The Dvāpara, Tretā and Kṛta (Satya) Yuga-s are two, three and four times the length of the Kali Yuga respectively. Thus they together constitute 4,320,000 years. This is called a Catur-Yuga.
A thousand and a thousand (i.e. two thousand) Catur-Yuga-s are said to be one day and night of the creator Brahmā. He (the creator) lives for 100 years of 360 such days and at the end, he is said to dissolve, along with his entire Creation, into the Eternal Soul or Paramātman.
The Hindu Calendar descends from the Vedic times. There are many references to calendrics in the Vedas. The (6) Vedāṅga-s (auto Veda) called Jyotiṣa (literally, "celestial body study") prescribed all the aspects of the Hindu calendars. After the Vedic period, there were many scholars such as Āryabhaṭṭa (5th century CE), Varāhamihira (6th century) and Bhāskara (12th century) who were experts scholars in Jyotiṣa and contributed to the development of the Hindu Calendar.
The most widely used authoritative text for the Hindu Calendars is the Sūrya Siddhānta, a text of uncertain age, though some place it at 10th century.
The traditional Vedic calendar used to start with the month of agrahayan (agra=first + ayan = travel of the sun, equinox) or Mārgaśīṣa. This is the month where the Sun crosses the equator, i.e. the vernal equinox. This month was called mārgashirsha after the fifth nakshatra (around lambda orionis). Due to the precession of the Earth's axis, the vernal equinox is now in Pisces, and corresponds to the month of chaitra. This shift over the years is what has led to various calendar reforms in different regions to assert different months as the start month for the year. Thus, some calendars (e.g. Vikram) start with Caitra, which is the present-day month of the vernal equinox, as the first month. Others may start with Vaiśākha (e.g. Bangabda). The shift in the vernal equinox by nearly four months from Agrahāyaṇa to Caitra in sidereal terms seems to indicate that the original naming conventions may date to the fourth or fifth millennium BCE, since the period of precession in the Earth's axis is about 2500,800 years.
Regional variants 
The Indian Calendar Reform Committee, appointed in 1952 (shortly after Indian independence), identified more than thirty well-developed calendars, all variants of the Surya Siddhanta calendar outlined here, in systematic use across different parts of India. These include the widespread Vikrama and Shalivahana calendars and regional variations thereof. The Tamil calendar, a solar calendar, is used in Tamil Nadu and Kollavarsham Calendar is used in Kerala.
Vikrama and Shalivahana calendars 
The two calendars most widely used in India today are the Vikrama calendar followed in Western and Northern India and Nepal, and the Shalivahana or Saka calendar which is followed in Andhra Pradesh, Karnataka, Maharashtra and Goa.
In the year 56 BCE, Vikrama Samvat era was founded by the emperor Vikramaditya of Ujjain following his victory over the Sakas. Later, in a similar fashion, Satavahana king Gautamiputra Satakarni initiated the Saka era to celebrate his victory against the Sakas in the year 78 CE.
Both the Vikrama and the Shalivahana eras are lunisolar calendars, and feature annual cycles of twelve lunar months, each month divided into two phases: the 'bright half' (Śukla Pakṣa) and the 'dark half' (Kṛṣṇa Pakṣa); these correspond respectively to the periods of the 'waxing' and the 'waning' of the moon. Thus, the period beginning from the first day after the new moon and ending on the full moon day constitutes the Śukla Pakṣa, 'bright part' of the month; the period beginning from the day after Pūrṇimā (the full moon) until and including the next new moon day constitutes the Kṛṣṇa Pakṣa, the'dark part' of the month.
The names of the 12 months, as also their sequence, are the same in both calendars; however, the new year is celebrated at separate points during the year and the "year zero" for the two calendars is different. In the Vikrama calendar, the zero year corresponds to 56 BCE, while in the Shalivahana calendar, it corresponds to 78 CE. The Vikrama calendar begins with the month of Baiśākha or Vaiśākha (April), or Kartak (October/November) in Gujarat. The Shalivahana calendar begins with the month of Chaitra (March) and the Ugadi/Gudi Padwa festivals mark the new year.
Another little-known difference between the two calendars exists: while each month in the Shalivahana calendar begins with the 'bright half' and is followed by the 'dark half', the opposite obtains in the Vikrama calendar. Thus, each month of the Shalivahana calendar ends with the no-moon day and the new month begins on the day after that, while the full-moon day brings each month of the Vikrama calendar to a close (This is an exception in Gujarati Calendar, its month (and hence new year) starts on a sunrise of the day after new moon, and ends on the new moon, though it follows Vikram Samvat).
In Gujarat, Diwali is held on the final day of the Vikram Calendar and the next day marks the beginning of the New Year and is also referred as ‘Annakut’ or Nutan Varsh or Bestu Varash. In the Hindu calendar popularly used in North India the year begins with Chaitra Shukala Pratipadha (March – April).
Samvat calendars 
Samvat is one of the several Hindu calendars in India:
- Vikram Samvat: lunar months, solar sidereal years
- Shaka Samvat (traditional): lunar months, solar sidereal years
- Shaka Samvat (modern): solar tropical
- Bangla Calendar: solar tropical years
- Tamil Nadu/Kerala: solar tropical years such as Malayalam calendar
- Nepali calendar with Bikram Sambat: solar tropical years
Most holidays in India are based on the first two calendars. A few are based on the solar cycle, Sankranti (solar sidereal) and Baisakhi (solar tropical).
Months and approximate correspondence 
Indian months are listed below. Shaka and Chaitradi Vikram (UP, Rajasthan, Maharashtra etc.) start with Chaitra, Kartikadi Vikram (Gujarat) start in Kartika.
Nakshatras are divisions of ecliptic, each 13° 20', starting from 0° Aries. The purnima of each month is synchronized with a nakshatra.
Time cycles in India 
The time cycles in India are:
- 60-year cycle
- 6 seasons of a year
- about 60 days (2 months) in a season
- Month (lunar)
- 2 pakshas in a month, shukla (waxing) and krishna (waning)
- 15 tithis in a paksha (1-14, 15th is purnima or amavasya)
- 60 ghatikas (or 30 muhurtas or 8 praharas) in a 24-hour period (ahoratra).
- 30 Kala (approx) in 1 muhurta
- 30 Kastha in 1 kala
- 15 Nimisha in 1 kastha
Years are synchronized with the solar sidereal year by adding a month every three years. The extra month is termed as "Adhik Mass" (extra month). This extra month is called Mala Masa (impure month) in Eastern India.
Date conversion 
Converting a date from an Indian calendar to the common era can require a complex computation. To obtain the approximate year in the common era (CE):
- Chaitradi Vikram (past) : Chaitra-Pausha: subtract 57; Pausha-Phalguna: subtract 56.
- Shaka: add 78-79
- Kalachuri: add 248-249
- Gupta/Valabhi: add 319-320
- Bangla: add 593-594
- Vira Nirvana Samvat: subtract 527-526
- Yudhishthira Samvat: Subtract 3101 (Ascension of Lord Krishna at age 125) from common era
- Sri Krishna Samvat: Subtract 3226 (Birth of Lord Sri Krishna) from common era
- Balabhi Samvat: add 320 to common era
- Kyoto University Panchanga Converter Program
The Kali "Samvat" 
The Kali Era is not called a "Samvat" in common Indian usage, but since it Is also an era, it might be useful to mention it here too. The Hindu calendar article has more information on the Kali Era. The conversion is given here:
- Add 3101 or 3100 (using the same guidelines as above) to the Gregorian year to get the number of elapsed Kali years.
- Add 3102 or 3101 to get the current Kali yuga number.
- Remember that the former (of the above two) is the standard, as explained at the Hindu calendar article.
- This era also corresponds with Yudhisthira Samvat in which we have present year as 5115 (April 2013 AD)
- In Bihar, Uttar Pradesh, Rajasthan, and many northern region of India months are Purnimanta (means month ends on Purnima or Full Moon). In Gujarat, Maharashtra, and other parts of many south Indian region, months are Amanta (months end on Amavasya).
- In inscriptions, the years may be gata (past) or current.
National calendars in South and South East Asia 
A variant of the Shalivahana Calendar was reformed and standardized as the Indian National calendar in 1957. This official calendar follows the Shalivahan Shak calendar in beginning from the month of Chaitra and counting years with 78 CE being year zero. It features a constant number of days in every month (with leap years).
The Bengali Calendar, or Bengali calendar (introduced 1584), is widely used in eastern India in the state of West Bengal, Tripura and Assam. A reformation of this calendar was introduced in present-day Bangladesh in 1966, with constant days in each month and a leap year system; this serves as the national calendar for Bangladesh. Nepal follows the Bikram Sambat. Parallel months and roughly the same periods apply to the Buddhist calendars used in Burma, Cambodia, Laos, Sri Lanka and Thailand.
Correspondence between calendars 
As an indicator of this variation, Whitaker's Almanac reports that the Gregorian year 2000 CE corresponds, respectively with:
- Year 5101 in the Kaliyuga calendar;
- Year 2544 in the Buddha Nirvana calendar;
- Year 2543 in the Buddhist Era (BE) of the Thai solar calendar
- Year 2057 in the Bikram Samvat calendar;
- Year 1922 in the Saka calendar;
- Year 1921 (shown in terms of 5-yearly cycles) of the Vedanga Jyotisa calendar;
- Year 1407 in the Bengali calendar;
- Year 1362 in the Burmese Calendar;
- Year 514 in the Gaurabda Gaudiya calendar;
- Year 1176 in the Malayalam calendar or Kolla Varsham calendar.
See also 
- Hindu astrology
- Hindu chronology
- Hindu units of measurement
- List of Hindu festivals
- Ancient Vedic units of measurement
- Perpetual Calendar of 800 Years
- Time Measurement and Calendar Construction. Brill Archive. Retrieved 2011-09-18.
- Chatterjee, S.K. (1998). Indian Calendric System. Publications Division, Ministry of Information and Broadcasting, Government of India.
- Chia Daphne and Helmer Aslaksen (April 2001). "Indian Calendars: Comparing the Surya Siddhanta and the Astronomical Ephemeris" (PDF). Retrieved 2004-04-04.
- Basham, A.L. (1954). The Wonder that was India. Macmillan (Rupa and Co, Calcutta, reprint),., Appendix II: Astronomy
- Notable Horoscopes - Bangalore Venkat Raman - Google Books. Books.google.co.in. Retrieved 2012-08-13.
- Sarma (2008), Astronomy in India
- Charak, Dr. K.S. (1996). Essentials of Medical Astrology, Uma Publications, pp.5–6.
- Hindu Lunar Month Names
- Bhāgavata Purāṇa 12.2.29-33
- Yano, Michio, "Calendar, astrology and astronomy" in Flood, Gavin (Ed) (2003). Blackwell companion to Hinduism. Blackwell Publishing. ISBN 0-631-21535-2.
Further reading 
- Reingold and Dershowitz, Calendrical Calculations, Millennium Edition, Cambridge University Press, latest 2nd edition 3rd printing released November 2004. ISBN 0-521-77752-6
- S. Balachandra Rao, Indian Astronomy: An Introduction, Universities Press, Hyderabad, 2000.
- Rai Bahadur Pandit Gaurishankar Hirachand Ojha, The Paleography of India, 2 ed., Ajmer, 1918, reprinted Manshuram Manoharlal publishers, 1993.
- Hindu Chronology, Encyclopædia Britannica Eleventh Edition (1911)
- The Astronomical Basis of the Hindu Lunisolar Calendar