Age Calculator
Calculate your exact age in years, months, and days, and find out how many days until your next birthday.
How It Works
- 1
Enter your date of birth
Select your birth date. The 'As of' date defaults to today but can be changed.
- 2
View your exact age
See years, months, days, total days lived, and days until your next birthday.
- 3
Explore different dates
Change the 'As of' date to see your age at any past or future point.
Worked example: born 15 June 1990, as of 26 October 2026
Calendar age from 1990-06-15 to 2026-10-26, walking real months and leap days rather than dividing total days by 365.25.
- Whole years from 15 Jun 1990 to 15 Jun 2026 = 36 years.
- From 15 Jun 2026 to 15 Oct 2026 = 4 months; from 15 Oct to 26 Oct = 11 days.
- Age = 36 years, 4 months, 11 days.
- Next birthday = 15 Jun 2027 (232 days after 26 Oct 2026).
- Total days lived โ 13,282 (includes leap days in the span).
36 years, 4 months, and 11 days old on 26 Oct 2026, with 232 days until the next birthday.
Calendar age method
years = whole birthdays passed months = whole months after last birthday days = remaining days after those months
- dob
- date of birth
- asOf
- reference date (often today)
- nextBirthday
- next anniversary of dob on or after asOf
This is not "total days รท 365.25". Month lengths and leap days matter โ use the date-difference calculator when you need a raw day count between two arbitrary dates instead of Y/M/D age.
Age checkpoints from a 15 Jun 1990 birth date
| As-of date | Age |
|---|---|
| 15 Jun 2010 | 20 years, 0 months, 0 days |
| 15 Jun 2020 | 30 years, 0 months, 0 days |
| 26 Oct 2026 | 36 years, 4 months, 11 days |
| 15 Jun 2030 | 40 years, 0 months, 0 days |
How Age Is Calculated
Age is the number of completed years since birth, but the exact years-months-days breakdown needs real calendar math. Months have 28 to 31 days, and February 29 birthdays need a rule for non-leap years. This calculator uses March 1 for leap-day birthdays in non-leap years. It also shows total days lived, days until your next birthday, and age on any 'As of' date for records, retirement planning, or milestone checks.
Frequently Asked Questions
How is age calculated?
Age is calculated by finding the difference between your date of birth and today's date (or any reference date). The result is expressed in years, months, and days. A full year is completed on each birthday.
How does this calculator handle leap year birthdays?
If you were born on February 29 in a leap year, your birthday is treated as February 28 in non-leap years for the purpose of counting completed years.
Can I calculate age at a specific past or future date?
Yes, use the 'As of' date field to choose any reference date. This lets you calculate how old you were at a specific point in the past, or how old you will be on a future date.
How is age different from date difference?
Age reports years, months, and days since a birth date. Date difference reports the span between any two dates (often as total days). Use age for "how old am I?" and date-difference for contract durations or day counts.
How are leap-day birthdays handled?
People born on 29 February typically celebrate on 28 February or 1 March in non-leap years, depending on local rules. The calculator advances the civil calendar; confirm legal age rules for your jurisdiction when a leap-day birthday gates a right or benefit.
Can I use age with BMI or TDEE?
Yes. Adult BMI categories assume age 20+, and TDEE formulas take age in years as an input. Convert height/weight units first if needed, then use the BMI or TDEE calculator with your completed age.
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Calculation record
How this result is maintained
Calcflux publishes the formula, assumptions, limits, and primary references behind its tools. Automated tests guard the implemented calculation paths and known-answer cases.
- Maintained by
- Calcflux
- Verification
- Formula tests and boundary checks