Old Style and New Style Dates

Old Style And New Style Dates

Old Style (O.S.) and New Style (N.S.) are used in English-language historical studies to indicate either that the start of the Julian year has been adjusted to start on 1 January (N.S.) even though documents written at the time use a different start of year (O.S.) or that a date conforms to the Julian calendar (O.S.), formerly in use in many countries, rather than the Gregorian (N.S.).

The Gregorian calendar replaced the Julian in Catholic countries beginning in 1582. This change was also implemented in Protestant and Orthodox countries after a significant delay. In England and Wales, Ireland, and the British colonies, the change of the start of the year and the change over from the Julian calendar occurred in 1752 with the passage of the Calendar (New Style) Act 1750. In Scotland, the legal start of the year had already been moved to 1 January (in 1600), but Scotland otherwise continued to use the Julian Calendar until 1752. Many cultures and countries now using the Gregorian calendar have different old styles of dating, depending on the type of calendar they used before the change.

The Latin equivalents for O.S. and N.S., which are used in many languages, are stili veteris or stilo vetere, abbreviated st.v. and meaning "(of) old style", and stili novi or stilo novo, abbreviated st.n. and meaning "(of) new style". The Latin abbreviations may be capitalized differently by different users, e.g., St.n. or St.N. for stili novi. There are equivalents for these terms in other languages as well, such as the German a.St. ("alten Stils" for O.S.).

Excerpt of the cover page of a print of the Treaty of Lübeck (1629), with the Gregorian day (22) directly above the Julian (12), both before the name of the month, May. The treaty was concluded between Roman Catholic parties, who had already adopted the Gregorian calendar, and Protestant parties, who had not.