Julian ↔ Gregorian Date Converter
CalculatorsEnter the full date in either box; the other shows its equivalent.
Julian ↔ Gregorian Date Converter
Convert dates between the Julian and Gregorian calendars. Enter a date as recorded in a historical record and get the equivalent date in the other calendar. The correction is ten to thirteen days, depending on the century, and the converter applies the right one for the year entered. Enter the full date in either box — the record's date on the Julian side, or a modern date on the Gregorian side — and the other box shows its equivalent.
The two calendars
Why are there two calendars with different dates?
The Julian calendar drifted from the solar year by about 11 minutes annually. By 1582, this had accumulated to 10 days. The Gregorian calendar corrected the problem by changing the leap-year rules, but different countries adopted it at different times. The difference between the two calendars grew from 10 days in 1582 to 13 days by the 1900s.
Why does the day correction change by century?
The difference between the calendars grew as the Julian calendar continued using a leap-year rule that the Gregorian calendar corrected. The offset was 10 days in 1582, 11 days in 1700, 12 days in 1800, and 13 days by 1900.
Which calendar a record uses
How do I know which calendar a historical record uses?
A record’s calendar is determined by where and when it was written, not by where the person in it was born. A parish register kept in Kent in 1740 is Julian because England had not yet changed. A Catholic register kept across the Channel in the same year is Gregorian because France had changed in 1582. A Protestant German parish in 1690 is Julian; the same parish in 1710 is Gregorian.
For any historical date, determine what calendar the record-keeper was using at the time the record was written, then check the adoption date for that place. Catholic and Protestant territories adopted the Gregorian calendar at different times, and individual states varied, so the specific adoption date should be confirmed before relying on a conversion.
What to record
Should I record the converted date or the date in the record?
Standard practice is to record a date exactly as the source gives it and note the calendar or year system — “3 March 1700 (Julian)”, “10 February 1700 (OS)” — rather than replace it with the converted equivalent. The original form is what a later researcher will find when checking the same register, and a converted date with no note can be mistaken for a transcription error.
Conversion is for comparison. When dates from records using different calendars need to be compared, bringing them onto a single calendar makes the difference between them clear. The converted date can be recorded alongside the original, but it should not replace it without explanation.
The change of 1752
What happened when England changed calendars in 1752?
England and Wales adopted the Gregorian calendar in September 1752. Wednesday, September 2, 1752, was followed by Thursday, September 14, 1752. The eleven dates between them were omitted from the calendar.
The change also made January 1st the beginning of the legal year. Before 1752, the English legal year began on March 25th, so dates between January 1st and March 24th can have both an Old Style and a New Style year.
The eleven days
What happened to the eleven days between the last Julian date and the first Gregorian?
They never occurred, so nothing is dated to them. An English record apparently dated September 5, 1752 is either mis-dated or not English.
People alive across the change could have dates recorded differently before and after it. George Washington, for example, was born on February 11, 1731 under the calendar then in use in Virginia. After the 1752 change, his birthday was reckoned as February 22, 1732. The day component belongs to the Julian ↔ Gregorian conversion; the year component reflects the change from the Old Style to the New Style year.
Adoption by country
When did different countries adopt the Gregorian calendar?
Adoption occurred at different times by country and territory. Some major examples:
Catholic Europe: many countries adopted the Gregorian calendar in 1582, when Thursday, October 4th (Julian) was followed by Friday, October 15th (Gregorian).
Scotland: changed the legal new year to January 1st in 1600 but retained the Julian calendar until 1752.
England and Wales: 1752, changing both the calendar and the start of the legal year.
Russia: 1918.
Greece: 1923.
Adoption dates varied among individual states and territories, particularly in the German and Eastern European regions, and the calendar change and the change to a January 1st new year did not always happen at the same time. The place and date of the record should be considered before converting it.
Julian or Old Style
What is the difference between a Julian date and an Old Style date?
Julian refers to the calendar itself; Old Style refers to the way the year was numbered before the legal new year moved to January 1st. They are related, but they describe different things.
Julian ↔ Gregorian moves the day: the difference is ten to thirteen days, depending on the century. Use it when a record was written while the Julian calendar was in force and the date needs to be compared with a Gregorian one.
Old Style ↔ New Style moves the year: use it when a pre-1752 English or Welsh record falls between January 1st and March 24th and the question is which year it belongs to.
A date can need both. “5 February 1740/41” in an English register needs the year settled first and the day correction second.