An age in completed years and an observation date define a birth interval if the reported age is accurate. Use it to plan a search, not to establish a birth date.
The form sends only the date and age to this site for calculation. Do not enter names. No account or saved result; you can print this page.
The method, step by step
Birth must fall after the observation date minus (age + 1) years and on or before that date minus age years. Displayed bounds are inclusive. This uses the Gregorian calendar; a February day is clamped to the last day of the month where needed.
Fictional example: age 38 on 10 April 1901 → 11 April 1862 to 10 April 1863. Age 69 on 20 March 1930 gives 21 March 1860 to 20 March 1861. These intervals do not overlap: keep the conflict visible.
What to watch for
Rounded or inaccurate ages, a census reference date differing from the visit date or an old calendar change the interpretation. Birthday conventions for 29 February can differ too: check records and widen the search. Do not average conflicting ages.