Age Calculator

A free online age calculator. Enter your date of birth to instantly find your exact age in years, months, days, total weeks, and see the countdown to your next birthday.

Math & Numbers

How Age Calculation Works

Calculating exact age is more involved than simple year subtraction. A correct algorithm must account for whether the current year's birthday has already passed, the unequal lengths of months, and leap years.

For example, if you were born on March 15, 1990 and today is February 10, 2025, a naive calculation (2025 − 1990 = 35) would be wrong — your 35th birthday hasn't happened yet. The correct age is 34 years, 10 months, and 26 days.

The Formula

  1. 1Count full years between birth date and the reference date.
  2. 2If this year's birthday hasn't passed yet, subtract one year.
  3. 3Count remaining full months after the year count.
  4. 4Count remaining days after the month count.
Age = (Reference Date − Birth Date) → years, months, days

Common Uses

  • Verifying age for legal documents (driving licence, passport applications)
  • Checking eligibility requirements that have minimum or maximum age limits
  • Calculating duration between any two historical or future dates
  • Planning birthday milestones such as the 10,000-day mark

Need to calculate percentages? Try the Percentage Calculator →

Coming soon: How Different Cultures Calculate Age

A guide covering East Asian age reckoning, Korean age (세는나이), and Julian vs. Gregorian calendar differences — and how they affect legal and official documents.

Frequently Asked Questions

How is age calculated exactly?
The calculator finds the difference between your birth date and today (or any custom end date). It counts full years first, then remaining months, then remaining days — accounting for varying month lengths and leap years.
Can I calculate the age between two custom dates?
Yes. The "As of" date defaults to today but you can change it to any date. This lets you calculate age at a past or future point in time.
Does it handle leap years correctly?
Yes. Leap years are handled correctly, including February 29th birthdays. The total days count is always accurate.
What does "next birthday in X days" mean?
After calculating your age, the tool shows how many days remain until your next birthday from the selected end date.

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