How the age calculator works
The calculator counts the whole years and months from a date of birth to today (or any date you choose), then the days left over. It works the same way as counting birthdays on a calendar, so it correctly handles months of different lengths and leap years.
- Whole months: it counts how many monthly anniversaries of the birth date have passed. Twelve of those make a year.
- Days: it counts the days since the last monthly anniversary.
- Totals: it counts every day between the two dates, then divides by 7 for weeks.
The day of birth isn't counted as a day lived, so a baby is 0 days old on the day they're born and 1 day old the next day. That's the same way most official forms count age.
Worked example
Someone born on Tuesday 15 May 1990, on 23 October 2026:
- Their 36th birthday was on 15 May 2026, so they're 36 years old.
- Five monthly anniversaries have passed since then (15 June to 15 October): 5 months.
- From 15 October to 23 October is 8 days.
- Exact age: 36 years, 5 months, 8 days, or 13,310 days in total (1,901 weeks and 3 days).
- Next birthday: Saturday 15 May 2027, when they turn 37. That's 204 days away.
Birthdays on 29 February
If you were born on 29 February, your birthday only appears on the calendar every four years. In other years this calculator treats 1 March as your birthday, because that's the first day you've completed another full year. Plenty of people celebrate on 28 February instead, and some organisations may use that date, so check if it matters for something official.
A similar rule applies to monthly anniversaries for people born on the 29th, 30th or 31st of a month: in a shorter month, the anniversary is counted on the 1st of the following month.
Common age milestones in the UK
| Age | What you can do |
|---|---|
| 16 | Get your National Insurance number, and leave school (though in England you must stay in education or training until 18) |
| 17 | Start learning to drive a car on the road |
| 18 | Buy alcohol, get a tattoo, sit on a jury |
| 21 | Get the National Living Wage (£12.71 an hour from April 2026) |
| 66 | State Pension age for people born before 6 April 1960, rising to 67 between 2026 and 2028 |
Uses for an exact age
- Forms and applications: some ask for age in years and months, such as school admissions, insurance quotes and children's activities.
- Babies and toddlers: development checks and weaning advice are often given in weeks or months, so the totals table is handy for new parents.
- Future dates: change the "age on this date" box to see how old someone will be on a wedding day, a holiday or the start of a school year (in England, children start Reception in the September after they turn four).
- Milestone days: spot when you'll be 10,000 or 20,000 days old for a celebration with a difference.
Need the number of days between any two dates, or working days only? Use the date calculator. For a due date or how many weeks pregnant someone is, try the pregnancy due date calculator, and to add up shift times use the hours calculator.
Frequently asked questions
How do I calculate my exact age?
Count the full years since your last birthday, then the full months since your last birthday, then the days since the most recent monthly anniversary. Someone born on 15 May 1990 is 36 years, 5 months and 8 days old on 23 October 2026.
How many days old am I?
Count the days from your date of birth to today. Someone born on 15 May 1990 is 13,310 days old on 23 October 2026. Enter your own date above to see yours.
How do leap years affect my age?
The calculator counts real calendar days, so extra days in leap years are included automatically in your total days and weeks.
When is my birthday if I was born on 29 February?
In years that aren't leap years, this calculator uses 1 March, because that's when you complete another full year. Many people choose to celebrate on 28 February instead.
How old will I be on a future date?
Change the “age on this date” box to any date in the future and the calculator shows the exact age you'll be then.
Last reviewed October 2026 using 2026/27 figures. This calculator gives an estimate for guidance only.