By entering any year, a side-by-side calendar is generated showing the Old Style dates on top with the New Style dates on the bottom for each day of the week for each month of the year. Very handy for counting days in one Style or the other but this calendar calculator does not include any Style change over information.
Provides a brief explanation of the switch from Gregorian to Julian. Also gives a very detailed table which shows by nation and district, when the change from Old Style to New Style happened. This table is extremely useful.