Confusion on calendars.

[VonHoldinghausen]

Hi there.

I am at the moment a bit confused on calendar they used. To boil things down:
Was the difference 12 or 13 days to our modern?
When I look at the familys birthdays for example, on different places,
Some are 12 days behind our calendar and some are 13 days.
Did something happen during the time from, say 1890 to 1917?
Was the differenc at one time 12, and at another time 13 days?
Their wikipages for example gives Anastasia and Alexei a birtday that is 12
days behind, the other children 13 days.

Kind regards, Pontus

[starik]

Before the adoption of the Gregorian Calendar in 1918 Russia used the Julian Calendar. At the time Olga, Tatiana and Maria were born, that calendar was 12 days behind the Gregorian Calendar, but in 1900 the Old Style Julian Calendar had a leap year where February 28 was followed by the 29th. But in the Gregorian Calendar used by other countries there was no leap year in 1900, so it was March 1st. That put the Old Style Julian Calendar 13 days behind.

[VonHoldinghausen]

Thank you!
Suspected something like this was going on

Kind regards