This calendar converter turns a date written in one historical calendar into the others: Gregorian, Julian, Hebrew and French Republican. It also shows the day of the week and, for English and colonial records before 1752, how the date would have been written with Old Style double dating.
How to use it
- Choose the calendar the record uses.
- Enter the day, pick the month from that calendar's own months, and enter the year.
- Read the same date in the other three calendars, and the weekday.
- For a date before 1923, the converter asks where the record is from and tells you plainly whether that place still used the old calendar, and how an English record would have written the year.
When each region changed calendar
| Region | Last Julian day | First Gregorian day |
|---|---|---|
| Italy, Spain, Portugal, Poland | 4 October 1582 | 15 October 1582 |
| France | 9 December 1582 | 20 December 1582 |
| Protestant Germany, Netherlands, Denmark-Norway | 18 February 1700 | 1 March 1700 |
| Britain, Ireland and the American colonies | 2 September 1752 | 14 September 1752 |
| Sweden and Finland | 17 February 1753 | 1 March 1753 |
| Russia | 31 January 1918 | 14 February 1918 |
| Greece | 15 February 1923 | 1 March 1923 |
Borders moved and some provinces switched at other times, so treat this as a starting point and check the place in your record.
Worked example
In Britain, Wednesday 2 September 1752 (Julian) was followed by Thursday 14 September 1752 (Gregorian). Enter 2 September 1752 as a Julian date and the converter gives Wednesday 13 September 1752 in the Gregorian calendar: the same day, eleven days apart on paper.
A baptism on 10 February 1713 (Julian), as we count years today, appears in an English register as 10 February 1712/13. The legal year 1712 ran until 24 March, so the clerk wrote both years. The second year is the one to use in your tree.
Limits
The converter gives the calendar date a record states. It cannot know which calendar a clerk actually used, and in border regions and religious communities two calendars were often in use at once. Hebrew days start at sunset, so evening events may belong to the previous civil day.
Frequently asked questions
- Why are Julian and Gregorian dates different?
- The Julian calendar adds a leap day every four years, which makes its year slightly too long. By the 1500s it had drifted ten days from the seasons. The Gregorian calendar removed the extra days and skips three leap days every 400 years to stay in step. The gap grew to 11 days in 1700, 12 in 1800 and 13 in 1900.
- When did each country switch to the Gregorian calendar?
- Catholic countries such as Italy, Spain, Portugal and Poland switched in October 1582. Protestant German states, the Netherlands and Denmark-Norway mostly switched in 1700. Britain, Ireland and the American colonies switched in September 1752, Sweden in 1753, Russia in 1918 and Greece in 1923. Some regions switched at other dates, so check the place in your record.
- What does a date like 10 February 1712/13 mean?
- It is a double date. Until 1752 the legal year in England and its colonies began on 25 March, so a date in January, February or early March belonged to the previous legal year. Writers showed both years. 10 February 1712/13 is 10 February 1713 in modern reckoning.
- Can I convert a Hebrew date from a gravestone?
- Yes. Choose Hebrew, pick the month and enter the day and year as written (for example 15 Tishrei 5649). Hebrew days begin at sunset, so an event recorded in the evening can fall on the previous civil date.
- Why does a French Republican date show no equivalent?
- The French Republican calendar was only used from 22 September 1792 until the end of 1805. A year outside that span has no real date to convert to.
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