"Old-Style" and "New-Style" Dates

On this web-site, you will find many year-dates before 1752 specified with a slash-mark, apparently citing two years.  For example, "February 11, 1704/5."  This is short-hand notation to denote that the year listed on the original source was 1704, but in terms of our modern calendar, it was really 1705.

This comes about because of the adoption of the Gregorian calendar (replacing the old Julian calendar) in 1752 throughout most of the British Empire.   The Julian calendar was inaccurate -- leap-years had been added too frequently -- and by the middle 1700s, the Julian calendar was about 11 days behind celestial reality.   Furthermore, in most of the British Empire, the start of a new year was marked on March 25th, rather than on January 1st.  [Thus, March 24, 1704 was followed by March 25, 1705.]    For complete correction of dates between January 1st and March 24th (in the Julian calendar), some number of days (and one year) must be added.  To make it clear, historians often refer to these different date-conventions as "Old Style" (OS) or "New Style" (NS), depending upon whether no correction or complete correction has been made, respectively.  For example, in Colonial America (at least in sectors under British jurisdiction):

February 11, 1704 (OS)  =  February 22, 1705 (NS)

On this web-site, we do not make complete corrections of month and day, but we do try to note the NS year with dual-year designations, for events occurring between January 1st and March 24th, prior to 1752.

The situation is much more complicated and confusing at the interface between British and Continental activities (for example when British colonists dealt with Dutch colonists in America).   Why?   Because most of the Catholic countries of Europe changed to the Gregorian calendar in 1582.  For 170 years (1582 - 1752) both calendar systems were in use in different parts of Europe and European colonies.   To make matters more confusing, many countries adopted January 1st as the start of the new year before adopting the Gregorian calendar (e.g., in 1700 Scotland began marking the new year on January 1st, while the rest of Britain marked the new year on March 25th -- though both continued to use the Julian calendar until 1752 !).

For further explanation, visit these sites:



For an automatic date-conversion calculator (applicable to most of Britain and her colonies), visit this site:



Return to Homepage