Why months are ambiguous
Adding a month to 31 January has no unambiguous answer, and different software gives 28 February, 2 March or 3 March. Age counted in years, months and days uses the calendar convention: complete years first, then complete months, then the remaining days — which is what a person means by "two years and three months".
Total days is unambiguous and is shown alongside, because for anything being calculated rather than described, days are the safer unit.
Leap years and 29 February
Someone born on 29 February has a birthday on the calendar once every four years. Legally, most jurisdictions treat 1 March as the anniversary in common years; some use 28 February. It affects when someone reaches a legal age by a single day, and it is worth knowing rather than assuming.
Frequently asked questions
How is age in months and days worked out?
Complete years first, then complete months, then remaining days — the way people say it. Total days is shown too, since that is unambiguous.
What about a 29 February birthday?
Most jurisdictions treat 1 March as the anniversary in common years, though some use 28 February. It can shift a legal age by a day.
Why do two calculators disagree by a day?
Usually whether the end date is counted, or a timezone difference around midnight. Both dates here are read as calendar dates, with no time of day involved.
Something wrong with this tool, or an idea for it? Tell us