# Birth date calculator

Calculate a birth date from a date of death and an age at death, such as the age carved on a gravestone.

This tool runs in your browser. Files and dates you enter are never uploaded.

The birth date calculator works out when someone was born from the date they died and their age at death, the way ages are carved on gravestones: "aged 72 years, 3 months and 14 days". With years, months and days it gives one exact date; with fewer parts it gives the range of possible birth dates.

## How to use it

1. Enter the date of death.
2. Type the age as it is written, such as `aged 72y 3m 14d` or `72 yrs 3 mos`, and the calculator fills in the years, months and days for you. You can also enter them directly.
3. Read the birth date or birth range, and copy the GEDCOM version if you want to paste it into your tree.

## How it is worked out

The calculator counts back from the date of death: first the years, then the months, then the days. When a month is shorter than the day you are counting from, it uses the last day of that month, so counting one month back from 31 March gives 28 February (29 February in a leap year).

When the smallest part of the age is missing, the person could have been anywhere inside it. Someone "aged 72" who died on 15 June 1890 had turned 72 but not yet 73, so they were born between 16 June 1817 and 15 June 1818.

## Worked example

A gravestone reads: "Died 15 June 1890, aged 72 years, 3 months and 14 days."

- Count back 72 years from 15 June 1890: 15 June 1818.
- Count back 3 months: 15 March 1818.
- Count back 14 days: 1 March 1818.

The calculator gives 1 March 1818, written for genealogy software as `1 MAR 1818`.

## Limits

Ages at death were often reported by someone else and were frequently rounded or wrong by a year or more, especially for older people. Use the result to know where to look for a baptism or birth record, not as proof. The arithmetic does not convert between calendars; check the warning if the birth falls before the Gregorian calendar was adopted where the person lived.

## Frequently asked questions

### How do I work out a birth date from a gravestone?

Enter the date of death and the age carved on the stone. If the stone gives years, months and days, the calculator gives one exact birth date. If it gives only years, it gives the range of dates the person could have been born in.

### Why do I get a date range instead of a date?

An age of 72 means the person had passed their 72nd birthday but not their 73rd. They could have been born on any day in a twelve-month window, so the calculator shows the earliest and latest possible birth dates.

### Is the calculated date always right?

Only as right as the age. Ages on gravestones, in death registers and in censuses were often given by relatives, rounded, or simply wrong. Treat the result as a lead to check against a baptism or birth record.

### What is the GEDCOM date for?

It is the same result written the way genealogy software stores dates, such as BET 16 JUN 1817 AND 15 JUN 1818 for a range. You can copy it straight into a birth date field.

### Does it handle the Julian calendar?

The arithmetic counts days as written in the record. If the result falls before the region switched to the Gregorian calendar, the calculator warns you so you can convert it with the calendar converter.

Canonical: https://kleiobase.com/tools/birth-date-calculator