Calculate Birth Date: Help

This is a handy little tool to calculate an estimated date of birth given an event and the age of an individual at the time of that event. You just enter the information and the web page displays the estimated date. This calculation takes into account the varying lengths of the months.

If you omit the age in days but supply the age in months then the calculation assumes that at the time of the event the individual was at least the specified age, but not a month older. In this case the application displays only the estimated month and year of birth. If the date of the event is in the first half of the month, the estimated month is one month earlier than a simple subtraction would indicate.

if you only supply the age in years then the calculation assumes that at the time of the event the individual was at least that age in years, but not one year older. Since in this case the application only displays the estimated year of birth, if the event is in the first half of the year, the estimated year is one year earlier than a simple subtraction would indicate.