How age is calculated
Your age in years is the number of complete years since your date of birth. You become one year older on each anniversary of your birth, so someone born on 15 May 1990 turns 36 on 15 May 2026, not on 1 January.
The exact age goes further: after counting whole years, the calculator counts the whole months since your last birthday and then the remaining days. Because months are different lengths, this is a calendar calculation rather than a simple division.
The method step by step
- Years = the year of the chosen date − the birth year, minus 1 if the birthday has not yet happened that year.
- Months = the month difference, borrowing 12 months from the years if needed.
- Days = the day difference; if it is negative, one month is borrowed and the number of days in the previous month is added.
- Total days = the exact number of calendar days between the two dates.
- Total weeks = total days ÷ 7, rounded down. Total months = years × 12 + months.
- Next birthday = days from the chosen date to the next anniversary, along with the weekday it falls on.
Worked example 1: age today
Born 15 May 1990, age on Thursday 15 October 2026
Last birthday: 15 May 2026, when they turned 36
From 15 May to 15 October is exactly 5 months, so the exact age is 36 years, 5 months, 0 days
Total days lived = 13,302, which is 1,900 weeks and 437 months
Next birthday (37th): 15 May 2027, a Saturday, in 212 days
Worked example 2: a leap-day birthday
Born 29 February 2000, age on 15 October 2026
Exact age = 26 years, 7 months, 16 days
Total days lived = 9,725
In years without 29 February, this calculator treats 28 February as the birthday, so the 27th birthday is counted on Sunday 28 February 2027, 136 days away
For some legal purposes in the UK, a person born on 29 February is treated as reaching a new age on 1 March in non-leap years; check the rule that applies to you.
Worked example 3: a child's age
Born 3 December 2012, age on 15 October 2026
Exact age = 13 years, 10 months, 12 days
Total days = 5,064; total months = 166
They turn 14 on Thursday 3 December 2026, in 49 days
Ages that matter in the UK
- Check GOV.UK for the State Pension age that applies to your exact date of birth.
| Age | What changes |
|---|---|
| 16 | National Insurance number letter sent automatically; can leave school, although in England you must stay in education or training until 18 |
| 17 | Can learn to drive a car |
| 18 | Adult in law: vote, buy alcohol, sign contracts |
| 22 | Workplace pension auto-enrolment starts (if earning over £10,000) |
| 57 | Minimum age to access most private pensions from April 2028 (55 before then) |
| 66 to 67 | State Pension age, rising from 66 to 67 between 2026 and 2028 |
Common mistakes and tips
- Subtracting only the years. 2026 − 1990 = 36 is only correct once the birthday has passed in 2026.
- Dividing days by 365. This ignores leap years and drifts by about a day every four years; use the calendar method.
- Mixing up date formats. The UK writes dates as day/month/year, while the US uses month/day/year. Choose dates with the date picker to avoid confusion.
- To find someone's age on a specific past or future date (for example a school starting date or a pension date), change the 'age on this date' field.