Date of Birth Calculator
Find possible birth dates from an age recorded on a known date. Use completed years or a precise years, months and days breakdown.
Starts with an editable example. Replace the dates and rules with your own.
Your calculation
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Choose your dates.
Select your counting rules and calculate.
Calculation details
| Step | Value |
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How to use this calculator
Enter the date the age was recorded, choose the available precision and provide the age. Review all matching birth dates rather than assuming one.
A whole-year age identifies a date range. Exact age uses anchored calendar months with month-end clamping; short months can produce more than one matching birth date. Coverage is 1900-2100.
A worked example
Someone aged 30 completed years on November 4, 2026 was born from November 5, 1995 through November 4, 1996.
Can I recover an exact birthday from age alone?
No. Completed years leave a range. Even a month-and-day breakdown can be ambiguous under a clamping convention; the calculator lists those matches.
Which calendar and years are supported?
Gregorian input coverage is 1900-2100 unless the method states a narrower range. Results explain calendar conventions and local date boundaries. Astronomy uses a level horizon at sea level. CSV, print and copy retain the result rules; calendar files contain only calculated events. Nothing is scheduled automatically.
What happens to my dates?
Calculations run on your device. Saving a calculation is optional and keeps it in this browser. A setup link contains the dates and settings you entered; anyone with the link can read them. Use one tab per saved calculator. Clear saved data from Privacy & settings.