Age Calculator
Age Calculator gives an exact age in years, months and days between any two dates, along with the totals in weeks and days and how long remains until the next birthday. It handles month lengths and leap years correctly, including the cases most calculators get wrong.
Runs entirely in your browser — nothing you enter is uploaded.
CalculatorAbout calculating age
Dividing days by 365 is the obvious approach and it is wrong almost immediately: it ignores leap years and drifts by about a day every four, so a person in their forties comes out roughly ten days out. It also cannot express months at all, because months are 28 to 31 days long and no average is correct for a specific pair of dates.
The reliable method settles the months first: count the whole months elapsed, step the start date forward by exactly that many, then count the real calendar days remaining. Because the last step measures a genuine distance between two real dates, it is correct however long the intervening months were. Stepping by a month clamps to the end of the target month, so 31 January plus one month is the last day of February — which is what stops monthly anniversaries drifting forward past every short month.
Common questions
- Why can I not just divide the number of days by 365?
- Because it ignores leap years, drifting by roughly a day every four years, so someone in their forties comes out about ten days wrong. It also cannot produce a figure in months, since months vary between 28 and 31 days and no single average is correct for a particular pair of dates.
- How is the age of someone born on 29 February calculated?
- There is no 29 February in a common year, so a convention has to be chosen. Most English-speaking jurisdictions treat 1 March as the legal anniversary, which is what this calculator uses; some other systems use 28 February. It only matters on that one day a year, but it does decide the day such a person legally turns eighteen.
- Why is 31 January to 1 March one month and one day?
- Because one month after 31 January is the end of February, not a date in March — February has no 31st, so stepping a month clamps to the last available day. From there, 1 March is one further day. Clamping is what keeps monthly anniversaries from drifting forward each time they pass a short month.
- Can I use it for something other than a birthday?
- Yes. Any two dates work, in either direction, so it serves equally for time served in a role, the gap between two events, or a countdown to a deadline. The same arithmetic applies, and the days and weeks totals are often the more useful figures for a project than years and months.