Conversion between Julian and Gregorian calendars

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

This is a visual example of the official date change from the Julian calendar to the Gregorian

Conventions
  • 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 AD 8. Julian calendar dates before March AD 4 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

This table is taken from the book by the Nautical almanac offices of the United Kingdom and United States originally published in 1961.[1]

YearJulian dateGregorian dateDifference
−500March 5February 28
−500March 6March 1−5
−300March 3February 27−5
−300March 4February 28
−300March 5March 1−4
−200March 2February 27−4
−200March 3February 28
−200March 4March 1−3
−100March 1February 27−3
−100March 2February 28
−100March 3March 1−2
100February 29February 27−2
100March 1February 28
100March 2March 1−1
200February 28February 27−1
200February 29February 28
200March 1March 10
300February 28February 280
300February 29March 1
300March 1March 21
YearJulian dateGregorian dateDifference
500February 28March 11
500February 29March 2
500March 1March 32
600February 28March 22
600February 29March 3
600March 1March 43
700February 28March 33
700February 29March 4
700March 1March 54
900February 28March 44
900February 29March 5
900March 1March 65
YearJulian dateGregorian dateDifference
1000February 28March 55
1000February 29March 6
1000March 1March 76
1100February 28March 66
1100February 29March 7
1100March 1March 87
1300February 28March 77
1300February 29March 8
1300March 1March 98
1400February 28March 88
1400February 29March 9
1400March 1March 109
1500February 28March 99
1500February 29March 10
1500March 1March 1110
YearJulian dateGregorian dateDifference
1582October 4October 1410
1582October 5October 1510
1582October 6October 1610
1700February 18February 2810
1700February 19March 111
1700February 28March 1011
1700February 29March 1111
1700March 1March 1211
1800February 17February 2811
1800February 18March 112
1800February 28March 1112
1800February 29March 1212
1800March 1March 1312
1900February 16February 2812
1900February 17March 113
1900February 28March 1213
1900February 29March 1313
1900March 1March 1413
2100February 15February 2813
2100February 16March 114
2100February 28March 1314
2100February 29March 1414

Using the tables

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 takes you past a February 29 that exists only in the Julian calendar, then February 29 is counted in the difference. Years affected are those which divide by 100 without remainder but do not divide by 400 without remainder (e.g., 1900 and 2100 but not 2000).

No guidance is provided about conversion of dates before March 5, -500, or after February 29, 2100 (both being Julian dates).

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.

  1. H M Nautical Almanac Office (1974). Explanatory Supplement to the Astronomical Ephemeris. London. pp. 416-18.
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See also

References
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