How to Calculate Your Exact Age in Years, Months, and Days
Subtracting two dates sounds like subtraction. It is not, because months have different lengths and years occasionally have an extra day. The Age Calculator gives you the exact gap in years, months and days.
Why it is not simple arithmetic
Take someone born on the 31st of January, on the 1st of March. Are they one month and one day old, or one month and two days? It depends whether you count the month as January's thirty-one days or February's twenty-eight, and both answers are defensible.
The convention almost everyone uses is to count whole years first, then whole months, then the leftover days - so you borrow from the preceding month, whose length varies. That is why two calculators can disagree by a day around month ends, and why doing it in your head goes wrong more often than people expect.
Leap years add the rest. Between any two dates there may be one, several or no 29ths of February, and a calculation that assumes 365 days a year drifts by a day every four years. Over a fifty-year span that is nearly a fortnight.
Where you actually need it
Visa and immigration forms, which often want age in years and months at a specific date rather than today. Insurance and medical forms, where the exact figure changes a bracket. School enrolment, which turns on age at a cut-off date. Legal documents, where "as at" a date matters more than now.
The other common case is the reverse question: not how old someone is, but how long until something. A deadline, a due date, a contract end. That is the same arithmetic in the other direction, and the Date Difference Calculator is built for it.
The 29th of February problem
Someone born on the 29th of February has a birthday that exists one year in four, and the law does not agree with itself about which day it falls on in other years. Some jurisdictions treat the 28th of February as the birthday, others the 1st of March, and the difference genuinely matters for anything with an age threshold.
There is no universal answer. If it affects a legal or financial decision, the rule that counts is the one in the relevant jurisdiction, not the one a calculator chose.
Common questions
Why does my age differ by a day from another calculator?
Almost always a different convention for borrowing days at a month boundary, or one calculator including the end date and the other not.
Can I work out age at a past or future date?
Yes, and that is what most forms want. Set the second date rather than using today.
Does it count the birthday itself?
The day you turn an age is the day you reach it, so your age increases on the birthday and not the day after.
How many days old am I?
The calculator gives it. For a round number of days to a future date, work it out as a date difference instead.
Need your exact age for a form?