Date of Birth Calculator
Know your age but not the exact date? Enter your age in years, months, and days along with a reference date to reverse-calculate your estimated date of birth.
How to Find Your Date of Birth
Type your age in years, months, and days. Leave months or days as 0 if unknown.
Choose the date your age was measured — usually today. Click 'Today' for convenience.
The calculator subtracts your age from the reference date to estimate your date of birth.
How the Reverse Calculation Works
The Formula
Date of Birth = Reference Date − (Years + Months + Days). The calculator subtracts each component from the reference date using real calendar math.
Why results may vary by ±1 day
Because months have different lengths (28–31 days), subtracting months can land on slightly different dates depending on the reference month. The result is the best estimate.
Examples
Basic example
Age: 25 years, 3 months, 10 days
Reference: March 10, 2026
Estimated DOB: November 30, 2000
Years only
Age: 40 years, 0 months, 0 days
Reference: March 10, 2026
Estimated DOB: March 10, 1986
Form filling
A form asks for your date of birth but you only know you are 33 years and 7 months old.
Enter 33y 7m 0d to get an estimate.
Historical date
Someone was 50 years old on January 1, 2000.
Estimated DOB: January 1, 1950
Frequently Asked Questions
Is the result exact?
If you know your exact age in years, months, and days, the result is very close — typically within ±1 day due to varying month lengths.
What if I only know my age in years?
Set months and days to 0. The result gives the date that is exactly that many years before the reference date.
Can I use a past reference date?
Yes. For example, if a document states someone was 30 years old on a specific date, enter that date as the reference.