Exact age, on any date you like
Age in whole years is easy. Age in years, months and days is where calculators start disagreeing with each other, because the leftover days depend on which months you passed through and how long they were.
This counts the leftover days from the monthly anniversary rather than from a flat thirty. So somebody born on the 15th who is asked about the 14th of a later month is a day short of the month, and whether that is 27, 29 or 30 days depends on which month it is. That is the honest answer, and it is why two calculators can both be right and still differ.
The second date does not have to be today
Set it back to work out how old somebody was at an event, or forward to check an age at a future date. That is the everyday use in employment and admin: how old will they be at the start date, were they over 18 on the day of the contract, what age do they reach in the next leave year.
Born on 29 February
A leapling has a real birthday roughly one year in four. In the other three, the birthday is taken as 1 March in England and Wales.
That follows from the Family Law Reform Act 1969, under which a person attains a given age at the start of the relevant anniversary date. Where 29 February does not exist that year, the anniversary is the 1st of March, so a leapling turns 18 on 1 March 2018 rather than 28 February. Scotland reaches the same result by a different route.
Some calculators use 28 February instead, which shifts the day somebody legally reaches an age by one. For a birthday card it makes no odds. For a date of majority, a pension trigger or a licensing threshold it does.
Where exact ages matter
National Minimum Wage bands step at 18 and 21, and the rate changes on the first pay reference period beginning on or after the birthday rather than on the day itself. Auto-enrolment into a workplace pension starts at 22. The State Pension age depends on date of birth and has moved several times.
Statutory redundancy pay is weighted by age: half a week per year worked under 22, one week from 22 to 40, and a week and a half from 41. Working out which band each year of service falls into needs the exact ages, not the round ones.
None of that is advice, and the thresholds change. What is on this page is arithmetic: the exact age, worked out properly, so whatever rule you are applying it to gets the right input.
Common questions
Why do two age calculators give different answers in months and days?
Because the leftover days depend on which months were passed through. This tool counts from the monthly anniversary rather than a flat thirty days, so the leftover depends on whether the months in between were 27, 29 or 30 days long.
Can I work out someone's age on a date other than today?
Yes. Set the second date back to find an age at a past event, or forward to check an age at a future date, such as whether someone will be over 18 on a contract start date.
When does someone born on 29 February have a birthday in a year that is not a leap year?
On 1 March, in England and Wales. Under the Family Law Reform Act 1969, a person attains a given age at the start of the relevant anniversary date, and where 29 February does not exist that year, the anniversary is 1 March.
Does it matter if a leapling's birthday is taken as 28 February instead of 1 March?
Yes, for anything with a legal threshold. It makes no difference for a birthday card, but it shifts the date somebody legally reaches an age, such as a date of majority, a pension trigger or a licensing threshold, by a day.
At what age do National Minimum Wage rates change?
At 18 and 21, though the new rate applies from the first pay reference period beginning on or after the birthday, rather than from the birthday itself.
How is statutory redundancy pay weighted by age?
Half a week per year worked under 22, one week per year from 22 to 40, and a week and a half per year from 41 onwards, so the exact age at each year of service decides which band it falls into.