Date calculator
Free · runs in your browser · nothing you type is uploaded
Birth date from an age
A death record, a census or a gravestone often gives an age instead of a birth date. Enter the date of that record and the age.
Ages in old records can be off by a year or more. Treat the answer as a clue to check against a baptism record.
Age at an event, or time between two dates
Day of the week
Records like “baptized the Sunday after his birth” make more sense when you know the weekday.
Julian ↔ Gregorian
Before a country switched calendars, its dates ran 10 to 13 days behind ours. Convert a date between the two.
When each place changed calendars
If a record is dated before the switch in its place, it's a Julian date.
| Place | Switched | Note |
|---|---|---|
| Spain, Portugal, most of Italy, Catholic Poland | October 1582 | 4 October was followed by 15 October. |
| France | December 1582 | |
| Netherlands: Holland, Zeeland, Brabant, Limburg (and Flanders in Belgium) | Dec 1582 – Jan 1584 | |
| Catholic German states and Austria | 1583 – 1585 | |
| Netherlands: Gelderland, Utrecht, Overijssel, Friesland, Groningen | 1700 – 1701 | Protestant provinces. Groningen switched in 1583, went back, and switched again in 1701. |
| Protestant German states, Denmark and Norway | March 1700 | 18 February was followed by 1 March. |
| Switzerland | 1584 – 1812 | Canton by canton. |
| Great Britain, Ireland and the American colonies | September 1752 | 2 September was followed by 14 September, and the new year moved from 25 March to 1 January. |
| Sweden (with Finland) | March 1753 | 17 February was followed by 1 March. |
| Russia | February 1918 | Church records of the Orthodox Church kept the Julian calendar longer. |
Go deeperHow the calendar math works
Every date is turned into a Julian Day Number: a plain count of days since 1 January 4713 BC. Both calendars map onto the same count, so converting between them is exact.
The Julian calendar adds a leap day every 4 years. The Gregorian calendar skips three of those every 400 years (1700, 1800 and 1900 weren't leap years; 2000 was). That's why the gap grows: 10 days in 1582, 11 from March 1700, 12 from March 1800, and 13 from March 1900.
Before 1752, England and its colonies also began the year on 25 March, which is where double dates like 1731/32 come from.
Jesus answered, Verily, verily, I say unto thee, Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God.
Questions
Why do some dates look like 1731/32?
That's double dating. Until 1752, Britain and its colonies started the year on 25 March, so a date between 1 January and 24 March was written with both years: 10 February 1731/32 means 1732 by today's reckoning.
What does "O.S." or "N.S." mean?
Old Style (Julian) and New Style (Gregorian). George Washington was born 11 February 1731/32 O.S., which is 22 February 1732 N.S.
How accurate are ages in old records?
Often not very. Census and death-record ages were given by whoever answered the door. Use the calculated birth year as a starting point and look for a baptism or birth record.