Calendar Change - 16th Century

The change in the calendar throughout the western world, during the late 16th to the middle of the 18th century, is often a source of confusion for beginning genealogists. Even experienced practitioners sometimes have difficulty explaining the matter, an understanding of which is vital to getting genealogical event dates correct. The purpose of this article is to describe the reason for the calendar change, how it affects genealogical dating of early events, and how to record events dated during the transition period.

Impact of the Calendar Change on Genealogy Records

The Julian Calendar (45 B.C. to 1582 A.D.) was used throughout the Middle Ages in most of Europe. Genealogists must be aware that during most of this Julian calendar period the New Year began on March 25, and March was designated the "first" month -- even though only the last seven days of March fell in the "new year" as then defined. More problematic, the inaccuracy of this calendar led to "drift" in seasonal dates such as Easter, which arrived later and later in the spring. A error of ten days had accrued before a corrected calendar was introduced.

The more accurate Gregorian calendar (1582 A.D. to present) was decreed by Pope Gregory XIII and accepted in most of western Europe. It solved the "drift" problem of the Julian calendar, and erased the cumulative error by deleting ten days at the end of the Julian calendar. The last day of the Julian calendar was 4 October and the following day was 15 October. It also officially mandated January 1 as the beginning of the New Year -- a practice that had begun earlier among businesses in many western countries. However, the Gregorian calendar introduced a problem for genealogists.

The problem was caused by the fact that non-Catholic western countries, particularly England and all of her colonies, were exceedingly disinclined to accept the scientifically correct, but "Roman" created calendar, they being suspicious of anything decreed by a Catholic Pope. After a delay of one-hundred-seventy years, England finally accepted the Gregorian calendar by a 1751 Act of Parliament. September 2, 1752 was set as the last day of the Julian calendar, and the following day was declared to be 14 September -- a deletion of eleven days. The eleven days came about because the long delay included the year 1700, introducing one more erroneous Leap Year day from the Julian calendar. Thus genealogists have to deal with a long period of ambigous record dates for English and colonial records from 1 January through 24 March, in years prior to 1753.

The early change to a January 1st New Year's day is said to have been largely motivated by business considerations, there being a large growth in world trade -- and business firms preferred a normal calendar year. The ambiguity of the year of record was resolved by using "split year" dating (sometimes called "double dating"). Thus, in the period between 1582 and 1752, businesses in countries still using the Julian calendar might date their records "February 14, 1714/15", which signaled they were using a Julian calendar, and thus the Gregorian date could be calculated as February 25, 1715. Local towns, counties, and courts in colonial New England also used split year dating, but the problem is that they were not consistent. The early introduction of split year dating by businesses, and the later introduction of the Gregorian calendar in Europe were well known to them, but exactly when they individually introduced strict split year dating was apparently uncoordinated. This leaves it to the genealogist to tread carefully in interpreting pre-1753 record dates.

Recording Split Year Dates

Around 1700 many New England town clerks began entering split-year dates. If one is found to be clearly entered, then use "21 February 1704/5" or whatever form the recorder used. For dates in the ambiguous, 1 January-24 March range without split dates, safe genealogical practice suggests using the notation "21 February 1704[/5]" when primary, direct evidence clearly suggests a split year applies, with an explanation in your footnote. If there is primary, indirect evidence that the split date applies but was omitted, then "21 February 1704[/5?]" would be appropriate, again with an explanation in a footnote. In general, the acceptable practice is to not convert pre-Gregorian dates to New Style, or (N. S.), but rather to record Julian dates with an Old Style, or (O. S.) notation suffix, for example, "She dated her letter 21 February 1714 (O.S.)". Conversion simply introduces another error opportunity, and further removes the information from its original form. Other genealogists can handle the conversion, if they have the need.

A good example of the New Year's date-change challenge to genealogists would be the case cited by Jacobus (see Source, chap. 18). He warns about the practice of individuals who created family bible records for events bridging the pre-and-post 1752-3 transition period -- they often felt compelled to convert all O. S. dates to N. S. Therefore, one should be suspicious of bible records for, say ten children whose birth years range from 1743 to 1761, all appearing in the same handwriting. Almost certainly they were entered together some time following the 1761 birth, hence the pre-1753 births have been converted to N. S. One should not be surprised to find an original church baptism for one of the early children dated several days before the birth date listed in the family bible.


  • Wikipedia
  • Donald Lines Jacobus, Genealogy As Pastime and Profession, 2nd Ed. Rev., Genealogical Publishing Co., Inc., (Baltimore:1971).

For general information about date and calendar issues of interest to genealogists, see Dates And Calendars. WikiPedia has in-depth articles on the Gregorian Calendar and Julian Calendar.