Editing Old Style and New Style dates (section)

==Differences between Julian and Gregorian dates==
{{Main article|Gregorian calendar#Difference between Gregorian and Julian calendar dates}}
The need to correct the calendar arose from the realisation that the correct figure for the number of days in a year is not 365.25 (365 days 6 hours) as assumed by the Julian calendar but [[Tropical year#Mean tropical year current value|slightly less]] (c. 365.242 days). The Julian calendar therefore has too many [[leap year]]s. The consequence was that the basis for the calculation of the [[date of Easter]], as [[Easter controversy|decided in the 4th century]], had drifted from [[March equinox|reality]]. The Gregorian calendar reform also dealt with the accumulated difference between these figures, between the years 325 and 1582, by skipping 10 days to set the [[Ecclesiastical equinox|ecclesiastical date of the equinox]] to be 21&nbsp;March, the median date of its occurrence at the time of the [[First Council of Nicea]] in 325.

Countries that adopted the Gregorian calendar after 1699 needed to skip an additional day for each subsequent new century that the Julian calendar had added since then. When the British Empire did so in 1752, the gap had grown to eleven days;{{efn|Because 1600 was a leap year in both calendars, only one extra Julian leap day (in 1700) needed to be taken into account.}}  when Russia did so (as its [[civil calendar]]) in 1918, thirteen days needed to be skipped.{{efn|Because 1600 was a leap year in both calendars, three extra Julian leap days (in 1700, 1800 and 1900) needed to be taken into account.}}