Ayyám-i-Há refers to a period of four or five intercalary days in the Bahá'í calendar, where Bahá'ís celebrate the Festival of Ayyám-i-Há. The four or five days occur in between the 18th and 19th months of the calendar from sunset of February 25 to sunset of March 1 and allow for the Bahá'í calendar to be synchronized with the solar year with regular years of 365 days, and leap years of 366 days.
The Báb, the founder of the Bábí Faith, instituted the Badí‘ calendar in the Persian Bayán with 19 months of 19 days each and a period of intercalary days to allow for the calendar to be solar. The introduction of intercalation marked an important break from Islam, as under the Islamic calendar the practice of intercalation had been specifically prohibited in the Qur'an. The Báb did not, however, specify where the intercalary days should go. Bahá'u'lláh, who claimed to be the one foretold by the Báb, confirmed and adopted the Badi calendar in the Kitáb-i-Aqdas, his book of laws. He placed the intercalary days before the fasting month of `Alá, the nineteenth and last month, and gave the intercalary days the name "Ayyám-i-Há" or "Days of Ha".
 Symbolism and celebration
The nineteen months of the Bahá'í calendar are named after the attributes of God. Ayyám-i-Há, which means the "Days of Há" — Há is the Arabic letter corresponding to the English H — commemorates the transcendence of God over his attributes, since its name "Há" has been used as a symbol of the essence of God in the Bahá'í holy writings. Under the Arabic abjad system, the letter Há has the numerical value of five, which is equal to the maximum number of days in Ayyam-i-Há.
During the Festival of Ayyám-i-Há Bahá'ís are encouraged to celebrate God and his oneness by showing love, fellowship and unity. In many instances Bahá'ís give and accept gifts to demonstrate these attributes, and it is sometimes seen as a "Bahá'í Christmas" ,but many Baha'i s only exchange small gifts because gifts are not the main focus.  It is also a time of charity and goodwill and Bahá'ís often participate in various projects of a humanitarian nature.
- Esslemont, J.E. (1980). Bahá'u'lláh and the New Era (5th ed. ed.). Wilmette, Illinois, USA: Bahá'í Publishing Trust. pp. 178–179. ISBN 0-87743-160-4.
- "‘Days outside of time’ festival reveres eternal essence of God". February 24, 2012. Retrieved 2013-02-03.
- According to the definition of intercalary days in the Oxford Companion to the Year four of the five days are "epagomenal days" added to make the number of a calendar's days equal to the number of days in a year, and only the fifth day of Ayyám-i-Há is an intercalary day.
- Taylor, John (2000-09-01). "On Novelty in Ayyám-i-Há and the Badí Calendar". bahai-library.org. Retrieved 2006-09-24.
- Bahá'u'lláh (1992) . The Kitáb-i-Aqdas: The Most Holy Book. Wilmette, Illinois, USA: Bahá'í Publishing Trust. pp. 24–25. ISBN 0-85398-999-0.
- National Spiritual Assembly of the Bahá'ís of the United States (2006-03-05). "The Bahá'í Calendar". bahai.us. Archived from the original on 28 September 2006. Retrieved 2006-09-24.
- Universal House of Justice (1992). Notes of the Kitáb-i-Aqdas. Wilmette, Illinois, USA: Bahá'í Publishing Trust. p. 178. ISBN 0-85398-999-0..
- National Spiritual Assembly of the Bahá'ís of the United States (2006-06-28). "Baha'is mark New Year with charity, period of fasting". bahai.us. Archived from the original on 23 February 2007. Retrieved 2007-02-25.