Julian to Gregorian date converter

Old Style and New Style, and why they disagree

The Julian calendar made every fourth year a leap year, no exceptions. That is slightly too many leap days, so over centuries the calendar slipped behind the sun by about three days every four hundred years. By 1582 the spring equinox had drifted ten days from where the church expected it. The Gregorian reform fixed both problems at once: it deleted ten days, and it stopped century years from being leap years unless they divide by four hundred. A date written before a country adopted that reform is "Old Style"(O.S.); the modern equivalent is "New Style" (N.S.).

The eleven days England "lost" in 1752

Britain and its colonies, including the American ones, held out until 1752. By then the gap had grown to eleven days, so Parliament decreed that Wednesday 2 September 1752 would be followed directly by Thursday 14 September 1752. The popular story that crowds rioted shouting "give us our eleven days" is mostly myth, but the adjustment was real and it scrambled birthdays, rents, and contracts. It is the single most common stumbling block in English-language genealogy before the mid-eighteenth century.

Reading dates in old records

Because the new year also moved (England had started its legal year on 25 March, Lady Day, not 1 January), you will often see double dates in registers, like "24 February 1731/2". The first number is the old legal year, the second the modern one. When you convert an Old Style date here, add the gap shown for the period: ten days for most of Europe before 1700, eleven for Britain after 1700, thirteen for Russia and Greece in the twentieth century. The table above lists the exact switch date for each country so you can pick the right offset for the record in front of you.