About this calculator
"How old are you?" sounds simple until you need it exactly — for a form with an age cutoff, a school enrollment deadline, an insurance rule or a visa application. Exact ages are trickier than they look because months have different lengths and leap years insert extra days, so counting years, months and days by hand goes wrong surprisingly often.
This calculator does the calendar arithmetic properly: full years to the most recent birthday, then full months, then the remaining days. It also totals your life in days and weeks (most people are mildly startled by the day count), the weekday of your birth, and the countdown to your next birthday.
How to use it
- Enter the date of birth.
- Leave "age at date" empty to calculate the age today, or set it to check an age on any past or future date.
- Use the future-date trick for cutoff questions: "will she be 5 by Sep 1?" is this calculator with Sep 1 as the age-at date.
The formula
There is no single-division formula because calendar units are irregular: a "month" is 28–31 days and a year is 365 or 366 days. The reliable method is the one used here — step forward from the birth date by whole calendar years, then whole calendar months, and count whatever days remain.
Worked example
Born May 15, 1990, on Oct 20, 2026 the exact age is 36 years, 5 months, 5 days. That is 13,307 days lived — 1,901 weeks exactly — from someone born on a Tuesday. Their next birthday is Saturday, May 15, 2027, 207 days away.
Frequently asked questions
How do I calculate age for a school or sports cutoff date?
Set the "age at date" field to the cutoff date (for example Sep 1 of the school year). The exact age shown is the one the rule will use — leagues and schools almost always phrase cutoffs as "must be X years old on or before" that date.
What about people born on Feb 29?
Leap-day babies have a genuine birthday only in leap years. In other years, most legal systems treat Mar 1 (some, Feb 28) as the day they turn a year older. This calculator ages them on Mar 1 in non-leap years, following the most common convention.
Why does my "total months" not equal years × 12 + months exactly?
It does — total months is defined as whole calendar months lived: full years converted to 12 months each, plus the whole months since the last birthday, with leftover days shown separately. It will never divide total days by an average month length, which is the imprecise shortcut other tools sometimes take.
Can I calculate the age of something that is not a person?
Absolutely — the math only cares about two dates. People use it for pets (with the usual caveats about "dog years" being a myth), buildings, businesses and relationships. For pure date differences without the age framing, the Date Calculator also counts business days.