View source for Old Style and New Style dates

==Differences between Julian and Gregorian dates==
{| border="1" cellpadding="1" cellspacing="0" style="float: right; width: auto; margin-left: 1em;"
|+ '''Conversion of Julian to Gregorian dates'''
|- bgcolor=#CEDFF2
! width="170"|Time period (from 1 March of first year to 29 February of last year)
! width="50"|Сorrection, days
|-
| align="center"|1–100
| align="center"|-2
|-
| align="center"|100–200
| align="center"|-1
|-
| align="center"|200–300
| align="center"|0
|-
| align="center"|300–500
| align="center"|+1
|-
| align="center"|500–600
| align="center"|+2
|-
| align="center"|600–700
| align="center"|+3
|-
| align="center"|700–900
| align="center"|+4
|-
| align="center"|900–1000
| align="center"|+5
|-
| align="center"|1000–1100
| align="center"|+6
|-
| align="center"|1100–1300
| align="center"|+7
|-
| align="center"|1300–1400
| align="center"|+8
|-
| align="center"|1400–1500
| align="center"|+9
|-
| align="center"|1500–1700
| align="center"|+10
|-
| align="center"|1700–1800
| align="center"|+11
|-
| align="center"|1800–1900
| align="center"|+12
|-
| align="center"|1900–2100
| align="center"|+13
|-
| align="center"|2100–2200
| align="center"|+14
|}
The Julian calendar was formerly in use in many European countries and their colonies, rather than the Gregorian calendar, currently in use in most countries. Consequently and to avoid ambiguity, "Old Style" (O.S.) and "New Style" (N.S.) are sometimes added to historical dates to identify which system is being used (when giving a date in the period when both systems were in parallel use). This notation is used in Western European (and colonial) history: similar notations are in use for the equivalent conversions in Eastern Europe and Asia.

For a period of 170 years (1582 &ndash; 1752), both dating systems were in concurrent use in different parts of Western Europe and its colonies.  The Julian calendar had drifted by 11 days from the solar calendar (due to its surfeit of leap years), so the day and month differ between the systems as well as does the year. System conversion occurred in Eastern Orthodox countries as late as the twentieth century. 

Catholic countries such as Italy, Poland, Spain, and Portugal were first to change to the Gregorian calendar. Thursday, 4 October  1582 was followed by Friday, 15 October, 1582, with ten days "missing". Countries that did not change until the 1700s observed an additional leap year, necessitating eleven "missing days". Some countries did not change until the 1800s or 1900s, necessitating one or two more "missing days".

France changed from Julian to Gregorian Calendar on 9 December, 1582 J.U. where the next day was 20 December, 1582 G.R.. France used the French Republican Calendar from 22 September, 1792 G.R. to 31 December, 1805 G.R.. 

In [[Imperial Russia|Russia]], the terms "Old Style" and "New Style" have the same significance as elsewhere. The start of the year was moved to 1 January in 1700, but the Gregorian calendar was introduced there much later, in the Russian S.F.S.R.&mdash;on 14 February, 1918 (Gregorian calendar). Hence the [[October Revolution]] of 1917 is so called, despite having started on 7 November under the Gregorian calendar (October 25 [Julian calendar]). Articles about the October Revolution which mention this date difference tend to do a full conversion to the dates from Julian to the Gregorian calendar. For example the article "The October (November) Revolution" the ''Encyclopædia Britannica'' uses the format of "25 October (7 November, New Style);" to describe the date of the start of the revolution.

It is sometimes remarked that William Shakespeare and Miguel de Cervantes died on the same ''date'', 23 April, 1616, but not on the same ''day''. England was still using the Julian calendar in 1616, while Spain was using the Gregorian calendar. Cervantes actually died ten days before Shakespeare.