A GEDCOM date is text with a grammar. Written inside it, a date sorts correctly, lands on the Calendar page and reads the same in the next program; written outside it, the date is still there, but every program has to guess. This page is the grammar, and what Tools > Standardize places and dates does with the dates that break it. The places half of the tool has a guide of its own.

The strict forms

Exact
12 MAR 1900, MAR 1900 or 1900: the day, the three-letter English month in capitals, the year.
Approximate
ABT 1900 (about), CAL 1900 (calculated from another fact), EST 1900 (estimated).
Before and after
BEF 1900, AFT 1900.
Range
BET 1900 AND 1905, one event somewhere in the span.
Period
FROM 1900 TO 1910, something that lasted; FROM 1900 or TO 1910 alone are allowed.
Interpreted
INT 1900 (the words as written), a reading of a phrase with the phrase kept.
Dual year
1750/51, a date written under both the old and the new start of the year.

What Standardize places and dates rewrites

Every date in the file is read. A date that parses but is not spelled the strict way is proposed in strict form; one that does not parse is tried as the shapes people type. Each proposal is a row, "was" and "will be", the "will be" yours to edit, and nothing is written until you tick it. Proposed:

  • The words spelled out: ABOUT, BEFORE, AFTER, BETWEEN, ESTIMATED and CALCULATED become their three-letter forms.
  • Full month names and ones with a period: 12 March 1900, Mar. 1900.
  • Month first: March 4, 1970.
  • ISO dates: 1900-03-12, always read as year, month, day.
  • Day, month and year as numbers with a slash, dot or dash: 12/3/1900, 12.3.1900, 12-3-1900.
  • A month and a year as numbers: 3/1900.
  • A GREGORIAN word in front, which is dropped because it is the default.

What it leaves alone

  • A difference of letter case or spacing only. 12 mar 1900 and abt 1900 are not proposed, because every program reads them.
  • Dates in other calendars, dates before the common era and free text are left as they are. Change dates on records are never touched. That covers Julian, Hebrew and French Republican dates, BCE years, anything in parentheses, anything that cannot be read as a date at all, and the dates in the file header.
  • Dual years, which are already strict.
  • Empty dates.

A date that reads two ways

03/04/1900 is the third of April to half the world and the fourth of March to the other half. The first step asks which way the file was typed: day first or month first. A numeric date is ambiguous when its first two numbers are both 12 or less and differ. Such dates are listed apart under "Could be read either way": the reading in your chosen order is filled into the "will be" box, the other reading is offered in the box's list, and none is written until you tick it. 13/04/1900 has only one valid reading and gets it whatever you chose, and 3/3/1900 is the same day either way.

Wrong dates are a different job

A date written strictly can still be impossible: a burial before the death, a mother of nine. Standardize changes spelling, not facts. The Issues page flags the impossible ones, and the impossible dates guide says which to fix first.

Next

Open Standardize places and dates and untick Places. The first step counts the dates that would change and the ones that could be read either way; the second shows each proposal with the strict form filled in.