Julian to Gregorian date converter: turn an Old Style (Julian) date into a New Style (Gregorian) date or back, for any year from 10000 BC to AD 9999, with the weekday, the Julian Day number, Modified Julian Day, Rata Die, English dual-dated years such as 1731/32, and which countries were on which calendar that day.
| Place | Switched | Days |
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Dates are for each place's civil calendar. Some countries switched region by region; the main dates are shown.
When did each country adopt the Gregorian calendar? The last Julian day and first Gregorian day for Italy, Spain, France, the Netherlands, Germany, Switzerland, Britain and its American colonies, Sweden, Russia, Greece and more, with a calendar of every switch and the days that were skipped.
Orthodox and Western Easter dates for any year: Catholic and Protestant Easter by the Gregorian computus, Orthodox Easter by the Julian computus in both calendars, Pentecost, the years the two Easters fall together, and how far apart they are.
| Year | Julian | Gregorian | Gap after February |
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| Event | Julian (O.S.) | Gregorian (N.S.) |
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Only the leap years. The Julian calendar adds 29 February every fourth year. The Gregorian calendar skips it in century years that don't divide by 400, such as 1700, 1800, 1900 and 2100. That keeps it in step with the seasons, while the Julian calendar slips about one day every 128 years.
13 days from 13 March 1900 to 13 March 2100 (Gregorian dates), so today's Julian date is 13 days behind today's Gregorian date. From 14 March 2100 the gap is 14 days. It was 10 days in 1582, 11 from 1700 and 12 from 1800.
Add the gap for that time: 10 days from 1582, then one more from each Julian 29 February that the Gregorian calendar skips, so 11 from 29 February 1700, 12 from 29 February 1800 and 13 from 29 February 1900. Carry into the next month when you pass its end: 25 October 1917 plus 13 days is 7 November. To go from Gregorian to Julian, subtract instead.
Because the Julian year is about 11 minutes too long, the spring equinox had drifted from around 21 March to around 11 March by the 1500s, pulling Easter away from the season fixed at the Council of Nicaea in AD 325. Pope Gregory XIII's bull Inter gravissimas, dated 24 February 1582, dropped 10 days and changed the leap-year rule. The plan was largely the work of Aloysius Lilius and Christopher Clavius.
The reform set the spring equinox back to about 21 March, where it fell around the time of the Council of Nicaea in AD 325, not where it had been in Julius Caesar's day. Between 325 and 1582 the Julian calendar had drifted by about 10 days. The gap has grown since because of the century years the Gregorian calendar skips.
Old Style and New Style. O.S. marks a Julian date and N.S. a Gregorian one. Before 1752 England also began the year on 25 March, so dates from 1 January to 24 March are often written with both years, like 11 February 1731/32, which is 11 February 1732 in today's counting.
In 1752, under the Calendar (New Style) Act 1750: Wednesday 2 September was followed by Thursday 14 September, in Britain and its colonies alike. The same act made 1 January New Year's Day from 1752. That's why George Washington, born on 11 February 1731/32 Old Style, has his birthday on 22 February.
Most Orthodox churches still work out Easter by the Julian calendar and its old moon tables, while Western churches use the Gregorian rule. In some years, such as 2025 and 2028, the two fall on the same Sunday; otherwise Orthodox Easter comes 1, 4 or 5 weeks later. From the 2400s the gap slowly widens.
Churches that keep the Julian calendar celebrate Christmas on 25 December Julian, which is 7 January Gregorian from 1901 to 2100. From 2101 it will fall on 8 January.
A plain count of days used in astronomy, starting at noon on 1 January 4713 BC in the Julian calendar, so 1 January 2000 is day 2451545. It comes from the Julian period that Joseph Scaliger proposed in 1583. Despite the name it isn't a Julian calendar date, and a Modified Julian Day is the same count minus 2400000.5, starting at midnight.
For church dates, yes. The Orthodox churches of Jerusalem, Russia, Serbia and Georgia, and the monasteries of Mount Athos, among others, keep their feasts by it. No country uses it for civil dates today.
Learn why the Julian and Gregorian calendars differ: the leap-year rules, why the gap is 13 days today and 14 from 2100, why 1582 dropped 10 days, what Old Style and New Style mean, why Orthodox Easter and Christmas fall later, and what a Julian Day number is.