Age Calculator

How age is counted

In the US, age is counted in completed years: you turn 30 on your 30th birthday, not during the year before it. The calculator finds the most whole months that fit between the birth date and the chosen date, splits them into years and months, then counts the days left over.

Months aren't all the same length, so the calculator steps forward from the birth date on the calendar rather than dividing days by 30. Someone born on the 31st completes a month on the last day of shorter months — born January 31, they are 1 month old on February 28 (or 29 in a leap year).

The totals — months, weeks and days — count the whole span. Total days is the number of days from the birth date to the chosen date, not counting the birth date itself, so a baby is 0 days old on the day it is born and 1 day old the next day.

Leap-day birthdays (February 29)

Someone born on February 29 has a calendar birthday only in leap years — years divisible by 4, except century years not divisible by 400. In other years there are two common conventions: celebrate on February 28, the last day of the birth month, or on March 1, the day after February 28.

This calculator uses February 28 by default, which matches how it handles every other month-end (January 31 plus 1 month is the last day of February). Choose March 1 if that is the convention you follow. The choice changes the result only in common years, and only between February 28 and March 1.

For legal purposes — a driver's license, retirement benefits, the age to buy alcohol — the rule that applies is set by the relevant law or agency, and it isn't the same everywhere. Check with the organization involved if a day matters.

Uses beyond birthdays

The same calculation gives the exact length of anything with a start date: how long you have worked somewhere, the age of a house or car, or how old a child will be on a school cutoff date. Set the "age on" date to the cutoff to check eligibility.

How the age is calculated

• Adding months uses the month-end rule: a day that doesn't exist in the target month becomes that month's last day.
• Next birthday = birth date + (years + 1) × 12 months.

Worked example

1. Born Friday, June 15, 1990. Age on October 11, 2026?
2. Whole years: the 36th birthday was June 15, 2026, and the 37th hasn't happened yet, so 36 years.
3. Whole months after that: July 15, August 15 and September 15 have passed, but October 15 hasn't, so 3 months (435 months in total).
4. Days: from September 15 to October 11 is 15 + 11 = 26 days (15 days left in September, then 11 in October).
5. Age: 36 years, 3 months, 26 days. That is 13,267 days, or 1,895 weeks and 2 days.
6. Next birthday: Tuesday, June 15, 2027, when they turn 37 — 247 days away.

Frequently asked questions