Conversion between Julian and Gregorian calendars

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The tables below list equivalent dates in the Julian and Gregorian calendars. Years are given in astronomical year numbering.

Conventions[edit]

  • Within these tables, January 1 is always the first day of the year.
  • The Gregorian calendar did not exist before October 15, 1582. Gregorian dates before that are proleptic, that is, using the Gregorian rules to reckon backward from October 15, 1582.
  • Years are given in astronomical year numbering.
  • Augustus corrected errors in the observance of leap years by omitting leap days until 8. Julian calendar dates before 8 are proleptic, and do not necessarily match the dates actually observed in the Roman Empire (Nautical almanac offices of the United Kingdom and United States, 1961, p. 411).

Conversion table[edit]

These tables are matching the table found in the book by the Nautical almanac offices of the United Kingdom and United States (1961, p. 417, JPEG).

Basic table containing only successive date intervals where differences are constant
or February 29 dates in Julian leap years that are not Gregorian leap years (emphasized rows)
Year Julian
date
Gregorian
date
Difference
in days
−900 March 1 February 24 −8
... ... ... −8
−700 February 28 February 23 −8
−700 February 29 February 24 −8
−700 March 1 February 25 −7
... ... ... −7
−600 February 28 February 24 −7
−600 February 29 February 25 −7
−600 March 1 February 26 −6
... ... ... −6
−500 February 28 February 25 −6
−500 February 29 February 26 −6
Year Julian
date
Gregorian
date
Difference
in days
−500 March 1 February 24 −5
... ... ... −5
−300 February 28 February 23 −5
−300 February 29 February 24 −5
−300 March 1 February 25 −4
... ... ... −4
−200 February 28 February 24 −4
−200 February 29 February 25 −4
−200 March 1 February 26 −3
... ... ... −3
−100 February 28 February 25 −3
−100 February 29 February 26 −3
Year Julian
date
Gregorian
date
Difference
in days
−100 March 1 February 27 −2
... ... ... −2
100 February 28 February 26 −2
100 February 29 February 27 −2
100 March 1 February 28 −1
... ... ... −1
200 February 28 February 27 −1
200 February 29 February 28 −1
200 March 1 March 1 0
... ... ... 0
300 February 28 February 28 0
300 February 29 March 1
Year Julian
date
Gregorian
date
Difference
in days
300 March 1 March 2 +1
... ... ... +1
500 February 28 March 1 +1
500 February 29 March 2
500 March 1 March 3 +2
... ... ... +2
600 February 28 March 2 +2
600 February 29 March 3
600 March 1 March 4 +3
... ... ... +3
700 February 28 March 3 +3
700 February 29 March 4
Year Julian
date
Gregorian
date
Difference
in days
700 March 1 March 5 +4
... ... ... +4
900 February 28 March 4 +4
900 February 29 March 5
900 March 1 March 6 +5
... ... ... +5
1000 February 28 March 5 +5
1000 February 29 March 6
1000 March 1 March 7 +6
... ... ... +6
1100 February 28 March 6 +6
1100 February 29 March 7
Year Julian
date
Gregorian
date
Difference
in days
1100 March 1 March 8 +7
... ... ... +7
1300 February 28 March 7 +7
1300 February 29 March 8
1300 March 1 March 9 +8
... ... ... +8
1400 February 28 March 8 +8
1400 February 29 March 9
1400 March 1 March 10 +9
... ... ... +9
1500 February 28 March 9 +9
1500 February 29 March 10
Year Julian
date
Gregorian
date
Difference
in days
1500 March 1 March 11 +10
... ... ... +10
1700 February 28 March 10 +10
1700 February 29 March 11
1700 March 1 March 12 +11
... ... ... +11
1800 February 28 March 11 +11
1800 February 29 March 12
1800 March 1 March 13 +12
... ... ... +12
1900 February 28 March 12 +12
1900 February 29 March 13
Year Julian
date
Gregorian
date
Difference
in days
1900 March 1 March 14 +13
... ... ... +13
2100 February 28 March 13 +13
2100 February 29 March 14
2100 March 1 March 15 +14
... ... ... +14
2200 February 28 March 14 +14
2200 February 29 March 15
2200 March 1 March 16 +15
... ... ... +15
2300 February 28 March 15 +15
2300 February 29 March 16


Other intermediate dates (can be inferred from table above)
Year Julian
date
Gregorian
date
Difference
in days
1500 March 1 March 11 +10
... ... ... +10
1582 October 4 October 14 +10
1582 October 5 October 15 +10
1582 October 6 October 16 +10
... ... ... +10
1600 February 18 February 28 +10
1600 February 19 March 1 +10
... ... ... +10
1700 February 18 February 28 +10
1700 February 19 March 1 +10
... ... ... +10
1700 February 28 March 10 +10
1700 February 29 March 11
Year Julian
date
Gregorian
date
Difference
in days
1700 March 1 March 12 +11
... ... ... +11
1800 February 17 February 28 +11
1800 February 18 March 1 +11
... ... ... +11
1800 February 28 March 11 +11
1800 February 29 March 12
1800 March 1 March 13 +12
... ... ... +12
1900 February 16 February 28 +12
1900 February 17 March 1 +12
... ... ... +12
1900 February 28 March 12 +12
1900 February 29 March 13
Year Julian
date
Gregorian
date
Difference
in days
1900 March 1 March 14 +13
... ... ... +13
2000 February 15 February 28 +13
2000 February 16 March 1 +13
... ... ... +13
2100 February 15 February 28 +13
2100 February 16 March 1 +13
... ... ... +13
2100 February 28 March 13 +13
2100 February 29 March 14


Using the tables[edit]

Dates near leap days that are observed in the Julian calendar but not in the Gregorian are listed in the table. Dates near the adoption date in some countries are also listed. For dates not listed, see below.

The usual rules of algebraic addition and subtraction apply; adding a negative number is the same as subtracting the absolute value, and subtracting a negative number is the same as adding the absolute value.

If conversion take you past a February 29 that exists only in the Julian calendar, then February 29 is counted in the difference.

No guidance is provided about conversion of dates before March 5, -500, or after March 28, 2100 (both being Julian dates).

Years not evenly divisible by 100, or evenly divisible by 400[edit]

For unlisted dates, find the date in the table closest to, but earlier than, the date to be converted. Be sure to use the correct column. If converting from Julian to Gregorian, add the number from the "Difference" column. If converting from Gregorian to Julian, subtract. When adding, remember every year that this section applies to is a leap year in both calendars so February 29 must be included in the addition if applicable.

Years evenly divisible by 100 and not divisible by 400[edit]

Every year that fits into this section is a Julian leap year and a Gregorian common year. In the table these years are including a February 29 day in the Julian date column, and these dates are listed with emphasized rows. For unlisted dates, find the date in the table closest to, but earlier than, the date to be converted. Be sure to use the right column.

When converting from Julian to Gregorian, add the number of days from the "Difference" column. If this date falls after the end of the Gregorian month, subtract the number of days of the Gregorian month and increment the month (and year if applicable). IF this date falls before the 1st day of the current month, then decrement the month (and year if applicable) and the number of days in this new month. Sometimes the difference column will be empty if the Julian date to convert is February 29 (it is in an emphasized row), meaning that the correction is not defined as a simple addition (in fact to convert it, first change February 29 into March 1 and add the Difference displayed on the previous row; this will give the equivalent Gregorian day in March, as listed in the Gregorian date column)

When converting from Gregorian to Julian, the process is just reversed, except that you lookup in the table the first date that comes before or at a date listed in the Gregorian column. Then you just need to substract the indicated number of days (counting them in the Gregorian Calendar) from your initial Gregorian date. But sometimes your date to convert will have no difference indicated in the table, and you can only use the date given in the Julian date column, which is a 29 February in the Julian calendar, for years that are leap in the Julian calendar, but not in the Gregorian calendar.

See also[edit]

References[edit]

  • Nautical almanac offices of the United Kingdom and United States. (1961). Explanatory Supplement to the Astronomical Ephemeris and the American Ephemeris and Nautical Almanac (pp. 410–8 ). London: H. M. Stationery Office.

External links[edit]