Julian to Gregorian Calendar Converter
Convert dates between the Julian and Gregorian calendar systems. Useful for historical research.
Julian ↔ Gregorian Calendar Converter
Result
2461317.5
Julian to Gregorian calendar converter
Formula
The Julian calendar, introduced by Julius Caesar in 45 BCE, had a leap year every 4 years. The Gregorian calendar, introduced by Pope Gregory XIII in 1582, refined this: a year is a leap year if divisible by 4, but not by 100 unless also by 400.
The difference between calendars accumulates:
- 1582-1699: 10 days
- 1700-1799: 11 days
- 1800-1899: 12 days
- 1900-2099: 13 days
- 2100-2199: 14 days
- And so on...
Worked example
Convert 10 October 1582 (Julian) to Gregorian:
- In 1582, the offset was 10 days
- 10 October + 10 days = 20 October
- Result: 20 October 1582 (Gregorian)
This is when the switch happened - the day after 4 October 1582 (Julian) was 15 October 1582 (Gregorian).
How to use
- Enter the date and select the calendar system
- Click "Convert" to see the conversion
Calendar difference table
| Year Range | Offset | Example | |------------|--------|---------| | 1582-1699 | 10 days | 1600 Julian = 1610 Gregorian | | 1700-1799 | 11 days | 1700 Julian = 1711 Gregorian | | 1800-1899 | 12 days | 1800 Julian = 1812 Gregorian | | 1900-2099 | 13 days | 1900 Julian = 1913 Gregorian | | 2100-2199 | 14 days | 2100 Julian = 2114 Gregorian |
Historical context
Different countries adopted the Gregorian calendar at different times:
- 1582: Italy, Spain, Portugal, Poland
- 1700: Germany, Denmark
- 1752: Great Britain and colonies (America)
- 1918: Russia (after the revolution)
- 1923: Greece
Common use cases
- Historical research
- Genealogy and family history
- Reading old documents
- Academic papers
- Legal document dating
FAQ
What is Old Style and New Style? O.S. = Julian calendar, N.S. = Gregorian calendar. Often written as "10 October 1752 O.S." or "21 October 1752 N.S."
Why the change? The Julian calendar had too many leap years, causing the calendar to drift relative to the equinoxes. The Gregorian reform corrected this.
When did America switch? The British colonies (including America) switched in 1752. September 2, 1752 was followed by September 14, 1752.
How do I write both dates? Use the dual dating format: "10/21 October 1752" or "10 October 1752 (O.S.)/21 October 1752 (N.S.)"
Is there still a Julian calendar? Yes, some Orthodox churches still use it for religious dates.
Can I convert backward? Yes, subtract the offset to convert Gregorian to Julian.