Date of Birth Calculator
Find a date of birth from a known age in years, months, and days. Enter current age or an age on a specific date to calculate the resulting birth date instantly.
Last updated: July 17, 2026
Find a date of birth from a known age in years, months, and days. Enter your current age or an age on a specific date below to calculate the resulting birth date.
Enter values and calculate
Fill in the form above and press Calculate to see your result.
How this calculator works
Enter a known age in completed years, months, and days, then choose whether that age applies today or on a specific calendar date. The calculator subtracts that age from the reference date to find the matching date of birth.
This is the inverse of the Age Calculator: instead of starting with a birth date, you start with an age and discover the birth date that produces it.
Worked example
If someone is 36 years, 7 months, and 17 days old on January 1, 2024, their date of birth works out to May 15, 1990. Switch to 'Age on a specific date' to anchor the calculation to any past or future day.
Leave 'Age as of' blank in current-age mode to use today's date automatically.
Understanding your birth date insights
Alongside the calculated birth date, the result card shows the weekday you were born on, the age breakdown at your reference date, your current age today, and how many days remain until the next birthday.
Use these facts to verify records, reconstruct missing birth dates from age notes, or cross-check against the Age Calculator once you know the birth date.
Practical use cases
Genealogy research, form completion when only an age is recorded, school admission reconstructions, and verifying identity documents all start with finding the birth date behind a stated age.
Pair this tool with the Age Calculator to move in either direction—birth date to age, or age to birth date.
Frequently asked questions
Enter the age in years, months, and days, choose whether that age applies today or on a specific date, and click Calculate. The tool subtracts that age from the reference date to return the matching date of birth.
Current age mode uses today—or an optional 'Age as of' date—as the reference point. Age on a specific date mode lets you enter any calendar day, such as a graduation, hiring date, or historical record.
The Age Calculator starts with a birth date and finds your age. This Date of Birth Calculator starts with a known age and finds the birth date—useful when you know how old someone was on a date but not when they were born.
Yes. The same calendar engine used across DateCalx handles February 29, varying month lengths, and completed years, months, and days.
After calculating, you see the weekday of birth, the age at your reference date, your current age today, and days until the next birthday.
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Written & Reviewed by
DateCalx Team
Editorial Team
The DateCalx Team researches, builds, tests, and reviews every calculator to ensure accurate, reliable, and easy-to-understand date and time calculations. Our goal is to provide fast, trustworthy tools for everyday personal, educational, and professional use.
Last reviewed: July 17, 2026
Learn more in our About, Editorial Policy, and Methodology pages, or contact the DateCalx Team.