The age formula

Age = Today's date − Birth date

This looks simple, but getting it exactly right requires handling years, months and days separately:

  1. Count the full years: Subtract the birth year from the current year. If the current month and day have not yet reached the birth month and day, subtract 1 from the year count.
  2. Count the remaining months: Calculate how many full months remain after the last birthday.
  3. Count the remaining days: Count the days since the last complete month.

Step-by-step example

Suppose today is August 4, 2026 and you were born on March 15, 1990.

  1. Years: 2026 − 1990 = 36. August (8) is after March (3), so no adjustment. You are 36 years old.
  2. Months: After your last birthday on March 15, 2026, the next full month is April 15 to May 15 (1 month), May 15 to June 15 (2 months), June 15 to July 15 (3 months), July 15 to August 4 — that's less than a full month. So 4 complete months.
  3. Days: From July 15 to August 4: July has 16 remaining days (31 − 15) plus 4 days in August = 20 days.

Result: 36 years, 4 months, 20 days

Leap years and age

A leap year occurs every 4 years (with exceptions for century years not divisible by 400). Leap years add February 29, which affects age calculation in two ways:

  • Born on Feb 29: In non-leap years, your birthday is treated as March 1 for age purposes. In leap years, it remains February 29.
  • Counting total days: Each leap year in your lifetime adds one extra day. Someone born in 2000 has lived through 6-7 leap days by 2026.

Using the calculator

Instead of calculating by hand, use the Age Calculator. Enter your birth year, month and day, and the calculator instantly shows your age in years, months, days, total weeks and total days.

For calculating your age on a specific past or future date, use the Age on a Specific Date Calculator.