Date of Birth Calculator
Find a birth date from a known age, or calculate age from a birth date using calendar-aware date math.
This is useful for records, age checks, personal timelines, and quick age verification.
Result
--
Run the calculation to see the result.
| Metric | Value |
|---|---|
| Years | -- |
| Months | -- |
| Days | -- |
| Total days | -- |
| Birth date | -- |
Quick Answer
If you know a person's age, this calculator can subtract that age from a reference date to estimate the date of birth. It can also work the other way and show age from a birth date.
How to Use It
- Choose whether you want a birth date or an age result.
- Enter the reference date.
- Enter the age in years, months, and days, or enter the birth date.
- Click Calculate.
Formula
Birth date = reference date - age
Age = reference date - birth date
Worked Examples
Example 1: A person who is 25 years, 3 months, and 2 days old on March 29, 2026 was born on December 27, 2000.
Example 2: Someone born on June 10, 1998 is 27 years, 9 months, and 19 days old on March 29, 2026.
Example 3: Setting the reference date to a school registration date lets you estimate age at that exact point in time.
How to Interpret Your Results
| Output | Meaning | Action |
|---|---|---|
| Birth date | The estimated date of birth. | Use it for records or follow-up checks. |
| Age breakdown | The age shown in years, months, and days. | Useful for forms and age verification. |
| Error | The inputs are invalid or out of order. | Check the dates and try again. |
Frequently Asked Questions
Related Calculators
References
- OmniCalculator reference page
- The calculator uses Gregorian calendar subtraction and addition.
- Last reviewed: March 2026.