What this age calculator does
Knowing someone’s age “in years” is easy; knowing it to the exact day is where mistakes creep in. This calculator takes a date of birth and returns the precise age in years, months and days, plus the totals — months, weeks and days lived — the day of the week the person was born, and how many days remain until the next birthday.
Everything runs in your browser, and you can point it at any date, not just today. That makes it handy for paperwork that hinges on a cutoff: school enrollment, insurance applications, retirement eligibility, or checking whether someone will already be 18 or 21 on the date of an event.
How to use it
- Pick the date of birth in the first field.
- Optionally set a reference date — the date you want the age calculated at. Leave it empty to use today.
- Read the exact age in the dark card, and the totals, weekday of birth and birthday countdown below.
The method: subtract, then borrow
Exact age works like long subtraction with dates, in three passes:
- Years: subtract birth year from reference year; take 1 away if this year’s birthday hasn’t arrived.
- Months: subtract the months; take 1 away if the reference day of the month is smaller than the birth day.
- Days: when you took that month away, “borrow” it — count using the length of the month before the reference month, then add the days elapsed in the reference month.
Worked example
Someone born on November 24, 2000, measured on July 7, 2026:
- Years: 2026 − 2000 = 26, but the November birthday hasn’t arrived yet, so it drops to 25 years.
- Months: from November to July is −4; borrow 12 to get 8, then take 1 away because day 7 is smaller than day 24 — 7 months.
- Days: count from June 24; June has 30 days, so 30 − 24 = 6 days, plus 7 days of July: 13 days.
Result: 25 years, 7 months and 13 days — a total of 307 months, 1,336 weeks or 9,356 days. That person was born on a Friday, and the next birthday (November 24, 2026) is 140 days away.
Days in each month
The borrowing step depends on month lengths, which is where manual age math usually goes wrong:
| Month | Days | Month | Days |
|---|---|---|---|
| January | 31 | July | 31 |
| February | 28 (29 in leap years) | August | 31 |
| March | 31 | September | 30 |
| April | 30 | October | 31 |
| May | 31 | November | 30 |
| June | 30 | December | 31 |
Frequently asked questions
How do I calculate age by hand?
Follow the three passes above: years first, then months, then days, borrowing the length of the previous month when needed. Double-check February and the 30-day months — that’s where nearly every manual error happens.
What about people born on February 29?
Leap-day babies only get a true calendar birthday every four years or so. In common years the convention differs by country: some jurisdictions treat February 28 as the legal birthday, others March 1. This calculator counts the next birthday as March 1 in non-leap years; the exact age itself is unaffected.
How many days are in a year?
A common year has 365 days and a leap year 366. Leap years come every 4 years, except century years not divisible by 400 — 2000 was one, 2100 won’t be. Averaged out, a Gregorian year lasts 365.2425 days, the figure to use for quick estimates.
Is age in months just total days divided by 30?
No. Calendar months vary from 28 to 31 days, so the correct figure is completed calendar months: years × 12 plus the leftover months from the exact-age result. Dividing by 30 overestimates the count for anyone more than a few years old.
Why does the reference date matter for forms?
Forms usually ask for your age on a specific date — the first day of school, the policy start date, the day of travel. Your age today can differ from your age on that date by a whole year if a birthday falls in between.