Gregorian Calendar Adoption by Country
When did each country switch from the Julian to the Gregorian calendar — and which days disappeared in the process? A country-by-country reference, from the original 1582 adopters through to the 21st century.
Why the reform happened
The Julian calendar, introduced by Julius Caesar in 45 BC, assumed an average year length of exactly 365.25 days. The real tropical year is about 11 minutes shorter, so by the 1500s the calendar had drifted roughly ten days ahead of the seasons — pushing the spring equinox, which the Catholic Church used to compute the date of Easter, away from its canonical 21 March.
Pope Gregory XIII's bull Inter gravissimas, issued on 24 February 1582, fixed both problems at once: it removed the accumulated ten days (Thursday 4 October was followed directly by Friday 15 October 1582 in Catholic countries), and it tightened the leap-year rule so that century years are leap years only when divisible by 400. Adoption beyond the Catholic states took centuries, and the table below shows when each country made the switch.
Adoption dates by country
| Country / region | Last Julian date | First Gregorian date | Days skipped |
|---|---|---|---|
Spain, Portugal, Polish–Lithuanian Commonwealth, most of Italy The original adopters under Pope Gregory XIII's bull Inter gravissimas. | Thursday, 4 October 1582 | Friday, 15 October 1582 | 10 |
France | Sunday, 9 December 1582 | Monday, 20 December 1582 | 10 |
Holy Roman Empire (Catholic states), Spanish Netherlands Catholic German states and the Southern Low Countries followed within weeks of France. | 21 December 1582 | 1 January 1583 | 10 |
Hungary | 21 October 1587 | 1 November 1587 | 10 |
Prussia | 22 August 1610 | 2 September 1610 | 10 |
Denmark–Norway | 18 February 1700 | 1 March 1700 | 10 |
Holy Roman Empire (Protestant states), Dutch Republic Protestant Germany used an improved astronomical Easter rule until 1776 before fully aligning with Rome. | 18 February 1700 | 1 March 1700 | 10 |
Great Britain and its colonies (incl. American colonies) The Calendar (New Style) Act 1750 also moved the start of the legal year from 25 March to 1 January. | Wednesday, 2 September 1752 | Thursday, 14 September 1752 | 11 |
Sweden (and Finland) Sweden's earlier gradual-adoption attempt (1700–1712) produced the unique date 30 February 1712 before reverting to the Julian calendar. | 17 February 1753 | 1 March 1753 | 11 |
Japan Replaced the Tenpō lunisolar calendar; the gap is zero because Japan moved directly between different calendar systems. | Meiji 5, 12th month, 2nd day (2 January 1873 OS) | Meiji 6, 1 January 1873 | — |
Republic of China Adopted alongside the founding of the Republic; the lunisolar calendar remained for traditional holidays. | — | 1 January 1912 | — |
Albania | November 1912 | December 1912 | 13 |
Bulgaria | 31 March 1916 | 14 April 1916 | 13 |
Ottoman Empire (fiscal calendar) A full civil switch followed under the Turkish Republic in 1926. | 15 February 1917 | 1 March 1917 | 13 |
Soviet Russia Decree of the Council of People's Commissars, 24 January 1918. The Russian Orthodox Church still uses the Julian calendar liturgically. | Wednesday, 31 January 1918 | Thursday, 14 February 1918 | 13 |
Estonia | 31 January 1918 | 14 February 1918 | 13 |
Kingdom of Serbs, Croats and Slovenes (Yugoslavia) | 18 January 1919 | 1 February 1919 | 13 |
Romania | 31 March 1919 | 14 April 1919 | 13 |
Greece Civil adoption only. The Church of Greece moved to the Revised Julian calendar in March 1924; Mount Athos and several other Orthodox churches still use the Julian. | 15 February 1923 | 1 March 1923 | 13 |
Turkey Replaced the Rumi fiscal calendar; the Islamic Hijri calendar remained for religious use. | 18 December 1926 | 1 January 1927 | 13 |
Saudi Arabia Adopted the Gregorian calendar for state administration and civil-servant payroll; the Islamic Hijri calendar remains the religious calendar. | — | 1 October 2016 | — |
Sources: Pope Gregory XIII, Inter gravissimas (1582); UK Calendar (New Style) Act 1750; Decree of the Soviet Council of People's Commissars (24 January 1918); national statutes and standard reference works on calendrical history.
What this means for genealogy and historical research
When you read a primary source from before a country adopted the Gregorian calendar, the date written on it is almost certainly a Julian (Old Style) date. Documents from the transition period often carried both — written as "11/22 February 1700" or with the suffixes O.S. and N.S.Be especially careful with:
- British and American records 1582–1752 — Britain stayed on the Julian calendar for 170 years after Catholic Europe switched, so the same calendar day in London and Rome could differ by 10–11 days.
- Russian records before February 1918 — events such as the "October Revolution" of 1917 actually fell in November on the Gregorian calendar.
- The English legal year — before 1752, the year in England rolled over on 25 March (Lady Day), not 1 January. A document dated "12 March 1700" in Old Style maps to 12 March 1701 in modern reckoning.
If you need to convert a specific Julian date to its Gregorian equivalent, our date tools and On This Day pages handle both calendar systems, including astronomical year numbering for BC dates.