---
title: "Julian to Gregorian Date Converter, Both Ways | Past Crumbs"
description: "Convert dates between the Julian (Old Style) and Gregorian (New Style) calendars, with every country's switch date and the 10 to 13 days between them."
url: https://pastcrumbs.me/julian-gregorian-converter/
---

Drawer II · Calendars

# Julian and Gregorian date converter

Turn an Old Style date into New Style, or back again. The card shows the weekday, how many days apart the calendars were, and which countries used which calendar on that day.

## When each country switched

The last Julian day and the first Gregorian day, with the weekdays: the weekly cycle never broke. Parts of Germany, the Netherlands and Switzerland changed at different dates, region by region, so check a local source for those.

| Country | Last Julian day | First Gregorian day | Dates left out | Notes |
| --- | --- | --- | --- | --- |
| Italy and the Papal States | Thursday 4 October 1582 | Friday 15 October 1582 | 10 | The first day of the reform decreed by Pope Gregory XIII in the bull Inter gravissimas (24 February 1582). |
| Spain | Thursday 4 October 1582 | Friday 15 October 1582 | 10 | Changed on the first day of the reform. |
| Portugal | Thursday 4 October 1582 | Friday 15 October 1582 | 10 | Then part of Spain's realms, it changed with Spain. |
| Poland | Thursday 4 October 1582 | Friday 15 October 1582 | 10 | Changed on the first day of the reform. |
| France | Sunday 9 December 1582 | Monday 20 December 1582 | 10 | Two months after Rome. Alsace followed in 1682 and Lorraine in 1760. |
| Prussia (the duchy) | Wednesday 22 August 1610 | Thursday 2 September 1610 | 10 | The Catholic German states had changed earlier, at various dates in 1583–1585. |
| Denmark and Norway | Sunday 18 February 1700 | Monday 1 March 1700 | 10 | Changed together. |
| Protestant German states | Sunday 18 February 1700 | Monday 1 March 1700 | 10 | With many local variations: check a local source for one town or territory. |
| Great Britain and its colonies | Wednesday 2 September 1752 | Thursday 14 September 1752 | 11 | By the Calendar (New Style) Act 1750, in all the king's dominions, the American colonies included. The same Act began the year on 1 January from 1752. |
| Sweden | Wednesday 17 February 1753 | Thursday 1 March 1753 | 11 | After a detour: Sweden left out the leap day of 1700, kept 1704 and 1708 by mistake, and went back to the Julian calendar with a 30 February in 1712. |
| Bulgaria | Thursday 31 March 1916 | Friday 14 April 1916 | 13 | By the 1900s, 13 days had to be dropped. |
| Russia | Wednesday 31 January 1918 | Thursday 14 February 1918 | 13 | In the eastern parts of the country the change may not have come until 1920. |
| Romania | Sunday 31 March 1919 | Monday 14 April 1919 | 13 |  |
| Greece | Wednesday 15 February 1923 | Thursday 1 March 1923 | 13 | The civil calendar. |
| Japan | Lunisolar calendar (never Julian) | 1 January 1873 | – | From the lunisolar calendar: the 3rd day of the 12th month of Meiji 5 became 1 January of Meiji 6 (1873). Japan never used the Julian calendar, so older Japanese dates are not converted here. |
| Turkey | An older year count (1341) | 1 January 1926 | – | Law No. 698 of 26 December 1925 adopted the international calendar for the official state calendar: the day after 31 December 1341 became 1 January 1926. Days and months already matched (31 December was followed by 1 January); the change was to the year count. |

## How far apart are the calendars?

The Julian calendar has a leap day in every century year; the Gregorian skips three in every 400 years. So the gap grows by a day in 1700, 1800 and 1900 (not 2000), always from the day after 28 February, and it reaches 14 days in 2100.

| Gregorian dates | The same days, Julian dates | Gregorian ahead by |
| --- | --- | --- |
| 15 October 1582 – 28 February 1700 | 5 October 1582 – 18 February 1700 | 10 days |
| 1 March 1700 – 28 February 1800 | 19 February 1700 – 17 February 1800 | 11 days |
| 1 March 1800 – 28 February 1900 | 18 February 1800 – 16 February 1900 | 12 days |
| 1 March 1900 – 28 February 2100 | 17 February 1900 – 15 February 2100 | 13 days |
| 1 March 2100 – 28 February 2200 | 16 February 2100 – 14 February 2200 | 14 days |

Going back before 1582 the gap shrinks the same way, so the Gregorian dates on this site for those years are proleptic: the two calendars give the same dates from 1 March 200 to 28 February 300 CE.

## How to use the converter

Choose the calendar your date is written in, then type the day and year and pick the month. The answer updates as you type. In English sources, O.S. (Old Style) marks the Julian reckoning and N.S. (New Style) the Gregorian.

Tick the Old Style box when your year comes straight from an English document written before 1752. Back then the year began on 25 March, so a letter dated 1 February 1720 was written in what we now call 1721. The box adds that year for dates from 1 January to 24 March; later dates are left as they are.

## Questions

**How many days apart are the two calendars today?**

Thirteen. The Gregorian date has been 13 days ahead since 1 March 1900 and stays so until 28 February 2100, when the gap becomes 14.

**Why did Britain drop 11 days but Rome only 10?**

Because Britain waited until 1752. In between came 1700, a leap year in the Julian calendar but not in the Gregorian, so the gap had grown by one day.

**How should I write a converted date?**

Quote the date as your document gives it, then add the other calendar's date in brackets or mark the two O.S. and N.S., so readers can check your working. For a dual year such as 1720/21, keep both years.

## Sources

- Jean Meeus, *Astronomical Algorithms*, 2nd edition (Willmann-Bell, 1998), chapter 7, “Julian Day”: the conversions, through the Julian Day Number, checked against Fliegel and Van Flandern, *Communications of the ACM* 11(10), 1968 ([doi:10.1145/364096.364097](https://doi.org/10.1145/364096.364097)).
- Claus Tøndering, [Calendar FAQ: the Gregorian calendar](https://www.tondering.dk/claus/cal/gregorian.php): the bull Inter gravissimas, every switch date in the table except Britain's, Alsace and Lorraine, Sweden's 1700–1712 detour, and the regional variations.
- [Calendar (New Style) Act 1750](https://www.legislation.gov.uk/apgb/Geo2/24/23), legislation.gov.uk, and Royal Museums Greenwich, [Which years are leap years?](https://www.rmg.co.uk/stories/time/which-years-are-leap-years-can-you-have-leap-seconds): Britain and its colonies, 2 September 1752 followed by 14 September, and the year beginning on 1 January from 1752.
- National Diet Library of Japan, [Calendar History 2](https://www.ndl.go.jp/koyomi/e/history/calendar.html): the 3rd day of the 12th month of Meiji 5 became 1 January of Meiji 6 (1873).
- Turkey, Law No. 698 of 26 December 1925, [text from the Grand National Assembly](https://www5.tbmm.gov.tr/tutanaklar/KANUNLAR_KARARLAR/kanuntbmmc004/kanuntbmmc004/kanuntbmmc00400698.pdf) (in Turkish): the day after 31 December 1341 is 1 January 1926.