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.
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.[1]
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.[2]
Year
Julian date
Gregorian date
Difference
−500
March 5
February 28
−500
March 6
March 1
−5
−300
March 3
February 27
−5
−300
March 4
February 28
−300
March 5
March 1
−4
−200
March 2
February 27
−4
−200
March 3
February 28
−200
March 4
March 1
−3
−100
March 1
February 27
−3
−100
March 2
February 28
−100
March 3
March 1
−2
100
February 29
February 27
−2
100
March 1
February 28
100
March 2
March 1
−1
200
February 28
February 27
−1
200
February 29
February 28
200
March 1
March 1
0
300
February 28
February 28
0
300
February 29
March 1
300
March 1
March 2
1
Year
Julian date
Gregorian date
Difference
500
February 28
March 1
1
500
February 29
March 2
500
March 1
March 3
2
600
February 28
March 2
2
600
February 29
March 3
600
March 1
March 4
3
700
February 28
March 3
3
700
February 29
March 4
700
March 1
March 5
4
900
February 28
March 4
4
900
February 29
March 5
900
March 1
March 6
5
Year
Julian date
Gregorian date
Difference
1000
February 28
March 5
5
1000
February 29
March 6
1000
March 1
March 7
6
1100
February 28
March 6
6
1100
February 29
March 7
1100
March 1
March 8
7
1300
February 28
March 7
7
1300
February 29
March 8
1300
March 1
March 9
8
1400
February 28
March 8
8
1400
February 29
March 9
1400
March 1
March 10
9
1500
February 28
March 9
9
1500
February 29
March 10
1500
March 1
March 11
10
Year
Julian date
Gregorian date
Difference
1582
October 4
October 14
10
1582
October 5
October 15
10
1582
October 6
October 16
10
1700
February 18
February 28
10
1700
February 19
March 1
11
1700
February 28
March 10
11
1700
February 29
March 11
11
1700
March 1
March 12
11
1800
February 17
February 28
11
1800
February 18
March 1
12
1800
February 28
March 11
12
1800
February 29
March 12
12
1800
March 1
March 13
12
1900
February 16
February 28
12
1900
February 17
March 1
13
1900
February 28
March 12
13
1900
February 29
March 13
13
1900
March 1
March 14
13
2100
February 15
February 28
13
2100
February 16
March 1
14
2100
February 28
March 13
14
2100
February 29
March 14
14
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.
