Determining and Expressing Dates

The topic of dates and how to estimate or calculate them has been addressed in NGS Monthly before. In Laura Murphy DeGrazia’s “Calculating Dates and Date Ranges,”[1] qualifying terms like “about” and “calculated” are referred to, but the article appropriately focuses on the actual calculations. Now we revisit the topic, but with a focus on how to express those calculations.

The case study at the end of this article revolves around Mary (–?–) (Adams) Ryan of late eighteenth- to early nineteenth-century New York City.[2] Research has revealed a fair amount about Mary, her family, and her life, but as of this writing no record of birth, baptism, first marriage, second marriage, death, or burial has yet been discovered for her. In the absence of those records, we can make educated estimates and narrow down date ranges in order to relay vital information about Mary.

When expressing estimated dates, the genealogical standard is to use one of a few modifying terms: by, between, about, or say, for example.

We use by when the estimate is based on the date of a related event that occurs after the vital event.

Example: Aaron Erin Beau-Baron’s widow first appears as such in the 1854 city directory (“Beau-Baron, wid. Aaron, 66 Macon Place”). So he died by 1854.

Warning: Some of these events are predictably close to their associated vital events, like probate proceedings or baptisms (for many Christian denominations). Other events may occur an indeterminate amount of time after their associated vital event—a divorce, for example.

A closely related term is between, which we use when there are two separate dates that frame an event.

Example: Aaron Erin Beau-Baron last appeared in tax records in 1852. Aaron’s widow first appears as such in the 1854 city directory. So he died between 1852 and 1854. (If you can determine the publication date of the city directory and the assessment date of the taxes, you can further specify the date range.

We use about when the estimate is based on specific age-related information given in a particular record.

Example: Dillon Dylan Beau-Billen was 67 in the 1850 census. So he was born about 1783.

Warning: Notice that this estimate doesn’t concern itself with whether the reported age of 67 is accurate. If the reported age is off by five years, so is the estimated birth.

We use say when the estimate is based on behaviors typical of a particular culture. We then add a parenthetical phrase referencing the basis for that estimate. For Americans from Europe until nearly the 20th century, women typically married at about 20 and men at about 25. They generally had their first child one year after marriage, and subsequent children were spaced two years apart.

Example: Thierry Teri Beau-Barrie’s eldest son Jerry was born 14 October 1814. If nothing else is known of Thierry, we can write that he was married say 1813 (birth of first known child) and born say 1788 (est. 25 at est. marriage).

Warning: As remarkably reliable as these estimates are, they don’t always apply. An estimate can be wildly off, and basing one estimate on another only creates and magnifies new errors.

Now back to Mary. Let’s take her life events one at a time.

When was Mary born? There are several ways this might be expressed. If we knew only that her oldest son, Joseph, was born about 1799, we could estimate that she married say 1798, so was born say 1778. If we have no idea whether Joseph is the oldest son or not, we could estimate that she married by 1798 and was born by 1778.

If we knew only that Mary was 26–44 in both the 1800 and 1810 federal censuses, then we could estimate that she was born about 1756­–1774 (1800 census) and born about 1766–1784 (1810 census). By overlapping the 18-year ranges of each census, we can shorten the expressed range to about 1766–1774, just an 8-year range.

What about Mary’s second marriage? When did that take place? The evidence to consider is that she had two children, James Ryan and Emeline Ryan, who were minors when she wrote her will 19 May 1833. When her will was proved 10 April 1839, James was among the adults involved in settling her estate. So James was born between 18 May 1812 and 10 April 1818. If James was born at least by 10 April 1818, then Mary was likely married to his father say 1811–1817.

As for Mary’s death, we just mentioned that she wrote her will 19 May 1833, and it was proved 10 April 1839. Her death date could be expressed as either between 19 May 1833 and 10 April 1839 or by 10 April 1839.

So what would a genealogical summary of Mary look like with no known maiden name and no known vital records?

Mary [—?—] was born about 1766–1774 (1800 and 1810 censuses) and died between 19 May 1833 and 10 April 1839 (will and will proved). She married first say 1798 (first known child’s estimated birth) [—?—] Adams. She married second say 1811–1817 (son’s calculated birth range) John Ryan.

Is it the most elegant piece of writing you’ll ever encounter? No. Is it informative and useful to your research? Yes.

Do you have people in your family tree about whom you “know nothing?” Try revisiting those ancestors and writing about them with these concepts in mind. You’ll find yourself beginning to define them, differentiating them from others, and narrowing down timeframes for more focused research.


[1] Laura Murphy DeGrazia, “Calculating Dates and Date Ranges,” NGS Monthly, June 2017 ( : 28 July 2019).

[2] Many details in this case study have been fictionalized for illustrative purposes. Accordingly, there are no source citations.

  1. August 22, 2019 6:52 pm
  2. September 11, 2019 11:17 pm

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