🎂 Age calculator — how old, down to the second
Put in a date of birth and a date to count to, and see the age in years, months and days — and then in days, hours, minutes and seconds, which is the same answer said in smaller pieces.
The age
The year you are in
The same age, in every unit
One age, said seven ways. The years, months and days on the card are the calendar answer; the rest are that same stretch of time counted in smaller pieces.
Calendar arithmetic, done on the dates as written: a day counts as 24 hours, no time zones are involved, and the hours and seconds are therefore a count of whole days rather than of clock time either side of a daylight-saving change. Months are counted the way an age is usually said, with the day clamped to the length of the month it lands in — a month from 31 January ends on 28 February, or on the 29th in a leap year — so somebody born on 29 February reaches an age on 28 February in the years that have no 29th, and this page counts 1 January to 1 January as exactly one year. Without a time, a date is read as the first moment of that day, and the count runs to that moment on the second date. None of this is a legal or medical definition of age: a document has its own rules, and the age the law uses is often reached the day before the anniversary, which is what the questions above are about.
Why use this calculator?
An age is not a subtraction. Take 15 January from 11 October and you get minus four, which is why the answer has to come from the calendar rather than from the digits: whole months are counted from the birth date, and what is left over is the days and the time. This page does that properly — leap years, month lengths and the awkward end-of-month cases included — and then says the same age in every unit there is, from years down to the seconds ticking beside you.
Why the arithmetic is fiddly
Dates are not numbers on a line, and three quirks do most of the work:
- A year is about 365.2422 days long, which is why a leap day is added every four years — except in century years that cannot be divided by 400. That makes 1900 the rare century that was not a leap year and 2000 the rarer one that was, and it means a year of age is 365 days or 366 depending on which stretch of the calendar you are in.
- Somebody born on 29 February has a birthday that does not exist in three years out of four. The chance of being born on a leap day is about one in 1,461 — four years of 365 days plus the one extra — and what to do about the missing day depends on where you are: this page counts 28 February, while some places and documents use 1 March.
- In law, an age is often reached the day before the anniversary. That comes from the English common law, and it is why a person born on 1 January is treated as having turned eighteen on 31 December. Worth knowing if the age you need is for a form rather than for a birthday card.
How does this calculator work?
Whole months first, then the days and the time left over:
age = the largest number of whole months that fits between the two dates, then the days, hours and minutes after that
Everything else on the page is that same figure said another way:
- A whole month is counted by moving the birth date along the calendar and clamping the day to the length of the month it lands in. A month from 31 January ends on 28 February, or on the 29th in a leap year — which is how an age is said out loud, rather than what a strict date library might do.
- The leftover days are counted from that last whole month to the second date, and the hours, minutes and seconds come from the time of day on each side. That is what the optional time boxes are for: without them, both dates are read as the first moment of the day.
- The totals for days, hours, minutes and seconds are the whole gap between the two moments, divided down. Every day counts as 24 hours, so no time zone or daylight-saving change can move them.
- Leap days are not counted anywhere; they are simply part of the calendar the months are counted along, so they arrive in the totals without being mentioned.
- The year you are in is the stretch between your last birthday and your next, and the bar is how far across it the second date sits — at 0% on a birthday, and back to 0% a year later.
- The seconds tick while the page is open, but only while the second date is set to today. Choose your own date and time and the figures stand still, because the moment being counted to is fixed.
Frequently asked questions
How is the age in years and months worked out?
By counting whole months from the birth date until the next one would overshoot the second date, then counting the days left over. Somebody born on 15 January 2000 counted to 11 October 2026 comes out as 26 years, 8 months and 26 days: 320 whole months fit between the two dates, and the last of them lands on 15 September 2026, which leaves 26 days.
Why does it ask for a time?
Because hours, minutes and seconds need one. With no time given, both dates are read as the first moment of the day, which is what most people want for a plain date-to-date answer. Put in a time of birth — or change the time of day being counted to — and the hours and minutes move with it, which is how the seconds figure stays honest.
What about somebody born on 29 February?
Their birthday only exists in leap years, so this page counts 28 February as the day in the other three years out of four, and says so in the fine print below the calculator. Some countries and documents use 1 March instead, and a few treat the birthday as the 28th for some purposes and the 1st for others — so for anything official, follow whatever the document asks for.
Does it count the day of birth itself?
An age is measured from the moment of birth, so on the day somebody is born they are hours old rather than a day old, and the age reaches its first whole day 24 hours later. That is why the years and months tick over on the birthday rather than the day before it, and why the day of birth is only counted once.
How many seconds have I lived?
That is the seconds figure under the result: the whole gap between the two moments, counted down through days, hours and minutes. Thirty years is about 947 million seconds, and because a year is slightly longer than 365 days, the leap days are already inside that number. While the second date is set to today, the figure counts up in front of you.
Is this the age a form or the law would use?
Not always. At common law an age is reached on the day before the anniversary, so a person born on 1 January has usually turned eighteen on 31 December, and some documents, pensions and competitions set their own cutoff date and time. For anything that matters, use the rule the form itself states rather than this page's arithmetic.
Why does another calculator give a different age?
Almost always a month-end or a time zone. From 31 January to 28 February this page says one month, because that is how a person says that age, while a date library that counts days would say 28 days — both are defensible, and there is no single standard. A calculator working in your local time zone can also come out a day different near midnight, because it is counting real hours rather than calendar days.