What this calculator does
Age in whole years is easy. Age in years, months and days is where it gets fiddly, because months are not a fixed length, so the remainder has to be counted forward from the last birthday rather than divided out of a day count. This calculator does that, and also gives the plain total in days, weeks and hours.
The second date is what makes it more than a birthday counter. Leaving it on today gives current age, but setting it to any other date answers how old someone was, or will be, on that date, which is what forms and eligibility rules usually need.
The formula
The years are the difference in calendar years, reduced by one if the birthday has not yet come round in the reference year. The months and days are then counted forward from that last birthday, borrowing from the preceding month where the day of the month has not been reached. The total days figure is a straight subtraction of the two dates, which is why it does not divide neatly into the years and months figure.
| Term | Meaning |
|---|---|
| Reference date | The date age is measured at, which defaults to today but can be any date. |
| Last birthday | The most recent anniversary of the birth date on or before the reference date, which the months and days are counted from. |
| Total days | A straight count between the two dates, unaffected by how months are grouped. |
The inputs explained
| Field | What to enter |
|---|---|
| Date of birth | The date of birth. |
| Age at this date | The date to measure age at. Leave it on today for current age, or set it to a future or past date to see age as at that date. |
When to use it
Checking age at a specific date
Eligibility for school years, licences, insurance bands and competition age groups is almost always assessed at a fixed date rather than today, so the reference date is the field that matters.
Getting an exact age for a form
Years alone are usually enough, but medical and legal forms sometimes want years and months, particularly for young children where a few months is a large proportion of the total.
Counting down to a birthday
The next birthday line gives the date and the days remaining from the reference date, which is the other half of what people usually want from an age calculator.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How old is each birth date on 1 January 2026?
Five dates of birth, all measured at the same reference date of 1 January 2026 so the figures can be compared directly.
| Date of birth | Age | In total days | Next birthday | Born on a |
|---|---|---|---|---|
| 1950-01-01 | 76 years, 0 months, 0 days | 27,759 | 1 Jan 2026: in 0 days | Sunday |
| 1975-06-15 | 50 years, 6 months, 17 days | 18,463 | 15 Jun 2026: in 165 days | Sunday |
| 1990-06-15 | 35 years, 6 months, 17 days | 12,984 | 15 Jun 2026: in 165 days | Friday |
| 2000-02-29 | 25 years, 10 months, 3 days | 9,438 | 1 Mar 2026: in 59 days | Tuesday |
| 2010-12-25 | 15 years, 0 months, 7 days | 5,486 | 25 Dec 2026: in 358 days | Saturday |
Questions
Why does the total days figure not match the years, months and days?
Because they measure differently. The total is a straight count of days between the two dates. The years and months figure groups those days into calendar units of unequal length, so a year can be 365 or 366 days and a month anywhere from 28 to 31. Both are correct, and neither converts cleanly into the other.
How is a leap-day birthday handled?
In a leap year the birthday falls on 29 February as normal. In a common year the calculator moves it to 1 March, which is the usual convention. Some jurisdictions treat 28 February as the legal birthday instead, so check the rule that applies if the distinction matters for eligibility.
Can I work out age at a date in the future?
Yes, set the reference date to it. This is the common case for age cut-offs, where a sporting age group or a school intake is assessed at a date some months ahead rather than at the date of application.
What happens if the birth date is after the reference date?
The calculator reports that rather than returning a negative age, since a negative age has no sensible reading. Swap the two dates if what you wanted was the gap between them.
For the plain gap between any two dates rather than an age, see the days between dates calculator. For the weekday and week number a date falls on, see the day of the week calculator.