Date & Calendar Converter
Convert between the Julian and Gregorian calendars (Old Style / New Style), decode French Republican dates, and calculate birth years from a stated age in a census or record.
Enter a date in the Julian calendar (Old Style) and get the equivalent Gregorian calendar (New Style) date.
Enter a date above and click Convert.
When did different countries switch?
- Catholic Europe (France, Spain, Portugal, Italian states, Poland): October 1582
- German Catholic states: 1583–1584
- German Protestant states, Denmark, Netherlands: 1700
- England, Wales & Ireland: September 1752 (14 Sep NS = day after 2 Sep OS)
- Sweden: February 1753
- Russia: February 1918
- Greece: February 1923
Double dating (England, Jan–Mar before 1752)
Before 1752, the English legal year began on 25 March, not 1 January. Dates in January–March may be written in double-date form such as 15 February 1750/51 (1750 Old Style year, 1751 New Style year). The calendar day conversion above does not alter year numbers — use the New Style year (the second number) when converting.
Enter a date from the French Republican calendar (used in France and occupied territories, Year I–XIV, 1792–1805).
Enter a date above and click Convert.
About the Republican calendar
The French Republican calendar was introduced on 22 September 1792 (Year I, Day 1). Each year had twelve months of exactly 30 days, plus 5 or 6 complementary days (jours complémentaires) at the end. Sextile (leap) years were III, VII, and XI. The Gregorian calendar was restored on 1 January 1806. Dates in this calendar appear frequently in Belgian, Dutch, and French civil registration records from this period.
Given a record year and a person's stated age, calculate the probable birth year range. Useful for census records, military rolls, and civil registers.
Enter a record year and stated age above.
Why a range?
A stated age in a record is almost never exact. A person recorded as age 45 in an 1881 census had their birthday in either 1835 or 1836 depending on whether their birthday had passed by the census date. Ages in older records may also be rounded or mis-stated. Search a range of at least ±2 years when using age-derived birth years as search criteria.