(Ancestry Blog – January 19, 2016)

What, you say, that can’t be right. Ancestors’ birthdays don’t just change, do they?

They might, if you’re looking at the wrong calendar.

Most of us are familiar with a single calendar—the Gregorian calendar, the one we use today. But, depending on the country, not all that long ago, your loved ones might have been living with the Julian calendar.

Setting a Date

Just like our current Gregorian calendar, the Julian calendar was based on the vernal (spring) equinox. But the Julian calendar listed March as the first month of the year. Leap years were employed to help keep months aligned with the seasons, but one leap year every four years wasn’t sufficiently accurate.

The Gregorian calendar, on the other hand, ensured that dates would be more accurately aligned with seasons. The Gregorian calendar also fine-tuned the leap year idea by removing three leap years out of every 400 years and by switching the first day of the year to 1 January rather than 25 March.

Confusing? Well the good thing is that calendar changes probably won’t affect you today—unless you’re a family historian. That’s when all of those date discrepancies and shifting numbers add up to a lot of confusion.

Consider this. An individual country may have adopted the Gregorian calendar any time between 1582 and the early 1900s. During the year the calendar was adopted, the country would have dropped 10 or 11 days from the year. But just like not every country adopted the Gregorian calendar at the same time, neither did any single country’s residents. And how those 10 or 11 days were dropped was completely up to the country making the change.

Take, for example, the calendar change that occurred on 4 October 1582, when Spain, Portugal, and Italy skipped 10 days, and each bumped their calendars to 15 October 1582. While 12 October 1582 did not technically exist in those countries, finding a document with that date while researching isn’t necessarily inaccurate—it could just mean that document was created by someone who waited a month or so to adopt the change.

So an ancestor’s birth date reading 5 October 1582 in one record and 16 October 1582 in another record may not signal a recording error. And double dates, recorded with slashes such as 15 March 1700/01, aren’t old-school typos—they’re used to show both Julian and Gregorian calendars.

Muddling Through

One of the greatest challenges a family historian finds when facing date changes is knowing—and understanding—when each ancestor’s country changed to the Gregorian calendar. The British colonies, including North America, didn’t move to the Gregorian calendar until 31 December 1751, which was then followed by 1 January 1752 (the Julian calendar would have read 1 January 1751—the year would have changed in March). The 11 days of inaccuracy from the Julian calendar were accounted for by omitting 2–14 September 1752. Alaska, which belonged to Russia when North American colonies made their switch, didn’t change to the Gregorian calendar until 1867.

Canada switched to the Gregorian calendar on 2 September 1752 and skipped immediately to 14 September 1752. France made the switch on 9 December 1582. The Catholic regions of Germany made the switch in various months of 1583 while most Protestant regions made the switch between 1615 and 1668. China never used the Julian calendar but started using the Gregorian calendar in 1912.

Adding Confusion

Quaker dates can be especially confusing since Quakers typically dated by number and because there was no official day on which every Quaker switched calendars.

“Before 1752, Quakers were using both calendars at the same time,” says family historian William Dollarhide. Using a number system, you may come across a date like 2/10/1720—on the Julian calendar, that date would be 10 April 1720; Gregorian, it would be 10 February 1720.

“I have come across a case where the only way I could tell if they were using a Julian or Gregorian calendar was to look through every other date in the record book to find some other numbers and see if those were Gregorian or Julian,” says Dollarhide. “It was a revealing experience to understand that for Quakers in particular you have to really watch the dates.”

Quaker dates may not be the only problematic ones you come across. But you can still get through calendar changes without too many problems, especially if you keep a couple of things in mind—how and when the country you’re looking at addressed calendar changes; and that a date, while perplexing, is still just a date.