Gregorian to Julian calendar date converter
Enter a Gregorian date to see its Julian (Old Style) equivalent, useful for Orthodox feasts and historical research.
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How to use it
- Enter gregorian date.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Compute the Julian Day Number of the Gregorian date, then express it in the Julian calendar, where every year divisible by 4 is a leap year. The gap is 13 days from 1 March 1900 to 28 February 2100, and was 10 days at the 1582 reform.
Example
Inputs: Gregorian date = 2026-10-01. Result: Converted date: 18 September 2026; Julian date (numeric): 2026-09-18; Days between the calendars: 13.
Limits and caveats
- Range year 1000 to 3000; Gregorian dates before 1582 are proleptic.
- Countries switched to the Gregorian calendar in different years, so check the switch date for the country concerned.
Questions about this tool
Why do some Orthodox churches keep Christmas on 7 January?
They follow the Julian calendar, and 25 December Julian is 7 January Gregorian between 1901 and 2100.
When does the gap become 14 days?
After 28 February 2100, because 2100 is a leap year in the Julian calendar but not in the Gregorian one.
What happened at the Gregorian reform?
Friday 15 October 1582 Gregorian came directly after Thursday 4 October Julian, a gap of 10 days.