Julian to Gregorian converter for Old Style and New Style dates
This free Julian to Gregorian converter turns a date in the old Julian calendar (Old Style) into the modern Gregorian calendar (New Style) and back — the conversion you need for family history, old letters and parish registers, Russian and Greek history, and the Orthodox churches that still keep the Julian “old calendar”. It shows the number of days between the two, the weekday, English double dating such as 11 February 1730/31, and which calendar a chosen country was using on that day.
Many people who search for a “Julian date” mean something else: the five-digit day-of-year code (YYDDD) printed on food, medicine and military paperwork, such as 26298 for 25 October 2026. The second mode reads and writes those codes.
How to use the Julian to Gregorian Calendar Converter
- Enter a Julian day, month and year, or pick a Gregorian date — the other side follows.
- Optionally choose a country in Calendar in use in to see which calendar was official there on that day.
- Read the converted date, the gap in days and any double-dating note, then press Copy result.
- For codes like 26298, switch to Day-of-year (YYDDD) and type the code or pick a date.
Julian to Gregorian Calendar Converter features
Old Style ↔ New Style
Exact conversion both ways for any date from year 1 to 9999, with the weekday and the Julian Day Number.
Double dating
Dates between 1 January and 24 March before 1752 are shown the English way, such as 1730/31.
Country change dates
When Italy, France, Britain, Sweden, Russia, Greece and others switched, and which calendar applies to your date.
Orthodox old calendar
The Julian date of any modern day, for churches that keep the Julian calendar.
Day-of-year codes
YYDDD and YYYYDDD to a date and back, with a two-digit-year setting.
Why the two calendars differ
The Julian calendar has a leap year every four years, making its average year 11 minutes too long. By 1582 the calendar had drifted ten days from the seasons, so Pope Gregory XIII dropped ten days — Thursday 4 October 1582 was followed by Friday 15 October — and skipped the leap day in century years not divisible by 400. The gap therefore grows by one day in 1700, 1800 and 1900 (not 2000): it is 13 days from 13 March 1900 (Julian 29 February) to 13 March 2100 (Julian 28 February), and 14 days after that. The weekday never changes.
Countries changed at different times. Catholic states switched in 1582, Denmark–Norway in 1700, Great Britain and its American colonies in 1752 (2 September was followed by 14 September), Sweden in 1753, and the Orthodox countries only in the twentieth century — Russia in 1918, Greece in 1923. Before 1752 the English year also began on 25 March, which is why George Washington’s birth is written 11 February 1731 (Old Style) or 22 February 1732 (New Style).
| Period (Gregorian) | Gregorian ahead by |
|---|---|
| 15 Oct 1582 – 10 Mar 1700 | 10 days |
| 11 Mar 1700 – 11 Mar 1800 | 11 days |
| 12 Mar 1800 – 12 Mar 1900 | 12 days |
| 13 Mar 1900 – 13 Mar 2100 | 13 days |
| 14 Mar 2100 – 14 Mar 2200 | 14 days |
The other “Julian date”
In industry and the military, a “Julian date” is simply the year and the day of the year: 26298 is the 298th day of 2026. It has nothing to do with the Julian calendar. For astronomers’ Julian Day (JD 2461338.5 and so on) use the Julian date converter; for Orthodox and Western Easter dates see the Easter date calculator.
Julian to Gregorian Calendar Converter FAQ
How do I convert a Julian date to a Gregorian date?
Type the Julian day, month and year; the Julian to Gregorian converter gives the New Style date. Between 1900 and 2100 you can also add 13 days.
Why is Orthodox Christmas on 7 January?
The churches that keep the Julian calendar celebrate on 25 December Julian, which is 7 January in the Gregorian calendar until 2100.
What does 1730/31 mean on an old document?
Before 1752 the English year began on 25 March, so dates in January to March were written with both years: 11 February 1730/31.
When did Britain switch to the Gregorian calendar?
In 1752: Wednesday 2 September was followed by Thursday 14 September.
What is today’s Julian date (YYDDD)?
Switch to Day-of-year and press Today; for 25 October 2026 the code is 26298.
Is the weekday different in the two calendars?
No. The same day has the same weekday in both; only the date number differs.