The calendar that we use today is the Gregorian calendar. It was introduced by Pope Gregory in 1582 to correct a major issue with the Julian calendar used before it.
The Julian calendar had become increasingly inaccurate from one decade to the next because of a problem with leap years and equinoxes. But the transition from the Julian to the Gregorian calendar wasn’t uniformly adopted worldwide.
Different countries switched at different times. Catholic countries like Spain and Italy changed straight away, but many predominantly Protestant countries waited nearly two centuries.
Gregorian Date Calculator
Why Genealogists Should Know The Differences
Because of the differences between calendars across different countries, exchanged documents may have confusing dates.
For example, suppose you have an exchange of letters between England and Spain in 1590. The reply could be dated before the first letter was sent.
A couple who married in one country and immediately emigrated to another may seem to have been unmarried when they arrived in their new country of domicile.
Caution With This Calculator
We’ve given you three major options in terms of region, but that doesn’t capture the complexity of all regions.
You also need to keep boundary changes in account. Some places may have changed from one country to a neighboring country.
You can get more details about when various regions switched here.