Dates And Calendars

This page summarizes a series of date and calendar issues of interest to genealogists. It includes links to other Encyclopedia of Genealogy entries that cover the issues in more detail, if such entries exist.

The Julian and Gregorian Calendars

The Julian calendar was introduced by Julius Caesar in 46 BC. It was supplanted by the more accurate Gregorian calendar beginning in 1582, although some countries continued using the Julian calendar until the 20th century.

Because both the Julian and Gregorian calendars were in use at the same time, a date will often be designated "Old Style" (O.S) if it is a Julian date or "New Style" (N.S.) if it is a Gregorian date.

For an explanation of genealogical issues related to the change from the Julian Calendar to the Gregorian calendar, see Calendar Change - 16th Century.

The Start of the New Year

The first day of the new year has changed a number of times. During the time span of the Julian Calendar, the most common "new year's day" was 25 March. Coincident with the change from the Julian Calendar to the Gregorian calendar, the first day of the new year was changed to 1 January. In the period between 1582 and 1752, written dates in countries still using the Julian calendar often included both the Julian and Gregorian year. For example, a date written in the American colonies as "February 14, 1714/15" means the Julian calendar was in use, and the date was 14 February 1714. The Gregorian date was February 25, 1715.

This topic is discussed further in the Calendar Change - 16th Century entry.

Other Calendars

Other calendars of interest include the Hebrew calendar, the Chinese calendar, and the Islamic calendar.

See WikiPedia's Calendar entry

Year Numbering - Regnal Years

Regnal years refer to years numbered according to the reign of a specific monarch. In the British Empire, for example, the second year of Queen Victoria's reign is 2 Victoria, and corresponds to the Gregorian date range 20 June 1838 to 19 June 1839.

Year, Month, and Day Sequence

In the United States, dates are often written in month, day, year sequence. In most of the rest of the world, dates are written in day, month, year sequence. When a numeric month is used, as in "12/7/1941", it is critical to know which sequence is in effect; does the date refer to December 7th, 1941, or July 12th, 1941? You have to know who wrote the date, or where, to know the answer.

Date Traps

A common practice is to use the date of one event as a proxy for another. For example, baptism dates are often used as an approximate birth date when the only evidence that has been located is a baptism record. Unfortunately, in some cases the baptism date is not clearly marked as such and a subsequent researcher may mistake the baptism date as the actual birth date. In extreme cases, the person in question may have been baptized as an adult.

Similarly, burial dates are often used as approximate death dates, and marriage bann dates are often used as marriage dates. If the dates are clearly labeled, the information is quite useful. If not, the errors that result can be difficult to correct.