About the Age Calculator
This free age calculator works out an exact age, or the difference between any two dates, in years, months and days — plus the totals in days and weeks.
Use a date of birth with today's date to get an age, or any two dates to measure a duration. It runs in your browser, so no date you enter is uploaded or stored.
Why "years, months and days" is harder than it looks
Counting days between two dates is simple arithmetic. Expressing the gap as years, months and days is not, because months are not a fixed length.
The standard method — and the one used here — works from the largest unit down:
- Count whole years from the start date until adding another would overshoot
- From there, count whole months the same way
- Whatever is left over is the days
Start on 15 January 2020, end on 10 March 2024. Four whole years reaches 15 January 2024. One more month reaches 15 February. From 15 February to 10 March is 24 days. Result: 4 years, 1 month, 24 days.
The consequence is that a "month" in the answer has no fixed value. The same span of days can produce different month-and-day results depending on which months it passes through, because February has 28 days and March has 31. This is why two calculators sometimes disagree by a day — they count in different orders. There is no single correct convention, which is why the total in days is often the more useful figure.
Leap years, and the 29 February problem
A leap year adds a day to keep the calendar aligned with the Earth's orbit, which takes about 365.2425 days rather than 365.
The rule has three parts, and most people only know the first:
- Divisible by 4 — leap year
- Except divisible by 100 — not a leap year
- Unless also divisible by 400 — leap year after all
So 1900 was not a leap year, while 2000 was. That exception is famous for breaking software, because a great deal of code implements only the first rule. Anything counting days across 1900 or 2100 with the simple rule will be wrong.
Then there are leaplings — people born on 29 February, who get a real birthday roughly every four years. When is their birthday in an ordinary year? There is no universal answer. Most jurisdictions treat 1 March as the legal date for reaching an age, on the reasoning that the full year has elapsed; some use 28 February. New Zealand and Taiwan use 28 February in law, while England and Wales use 1 March. Many people simply pick one and celebrate.
This calculator counts elapsed time rather than ruling on the legal question, so a 29 February birth date gives you the exact span either way.
What you can use it for
- Exact age — for a form, an application or an eligibility check
- Age on a future date — will someone be 18 by the date of an event?
- How long since — a job start date, an anniversary, a purchase, a move
- How long until — a deadline, a wedding, a due date, a retirement date
- Project spans — how long something has actually run
- Warranty and guarantee periods — is a purchase still covered?
- Pet ages — the same arithmetic works for anything with a start date
- Notice periods and probation — counting from a contract date
For business-day counting, which excludes weekends, use Business Days Calculator instead — this one counts every calendar day.
Ages are not counted the same way everywhere
Worth knowing if you deal with documents across countries.
Most of the world uses the Western system: you are 0 at birth and gain a year on each birthday. That is what this calculator computes.
East Asian age reckoning works differently. Traditionally a baby is 1 at birth and everyone gains a year at the new year rather than on their birthday — so someone born in December could be counted as 2 within weeks. South Korea used this system widely until June 2023, when it standardised on the international method for legal and administrative purposes. You may still meet the traditional count socially, and in older records.
There are other conventions in insurance and finance — "age nearest birthday" rounds to the closest one, so someone 34 years and 8 months is treated as 35. Always check which definition a form actually wants.
How to use it
- Pick the start date (e.g. a date of birth)
- Pick the end date (defaults to today)
- Read the result in years, months and days, plus totals
Good to know
- The end date counts as the boundary, not an extra day. From 1 March to 2 March is one day.
- Your age in days is a good conversation piece — 10,000 days is about 27 years and 4 months.
- Time zones are ignored, which is correct for dates. A birth date is the same date wherever you read it.
- Historical dates before 1582 can be ambiguous, because countries switched from the Julian to the Gregorian calendar at different times — Britain not until 1752, losing eleven days.
- For a legal deadline, check the local rule. Some count from the day of the event, others from the day after.
- Nothing is stored. Dates of birth are personal data, and this tool neither transmits nor saves them.
Common questions
How do I calculate my exact age?
Enter your date of birth as the start date and leave the end date as today. The result gives your age in years, months and days, along with totals in days and weeks. The calculation counts whole years first, then whole months, then the remaining days, which is the standard method used on official forms.
How does the calculator handle leap years?
They are counted exactly. Every 29 February in the span is included in the day totals, using the full rule: years divisible by 4 are leap years, except those divisible by 100, unless they are also divisible by 400. That last part is why 1900 was not a leap year but 2000 was — a distinction a surprising amount of software still gets wrong.
When is the birthday of someone born on 29 February?
There is no single answer, and it varies by country. England and Wales treat 1 March as the day a leapling reaches a new age, while New Zealand and Taiwan use 28 February. Socially, people simply choose. This calculator measures elapsed time rather than applying a legal rule, so the span it reports is exact either way.
Why do different calculators give slightly different results?
Because expressing a gap in years, months and days requires a convention, and months vary in length. Counting years first, then months, then days is the usual approach, but a calculator that counts in a different order can land a day apart. The total number of days is unambiguous, which is why it is often the more dependable figure.
Can I calculate a date difference in the future?
Yes. Any two dates work in either direction, so you can measure how long until a deadline, a wedding or a due date just as easily as how long since something happened. Setting a future end date also answers questions like whether someone will have turned 18 by a particular event.
Does it count working days or all days?
All calendar days, including weekends and holidays. For a count that excludes weekends — useful for notice periods, delivery estimates and contractual deadlines — use the Business Days Calculator instead.
Is my date of birth sent anywhere?
No. The calculation happens entirely in your browser, and nothing is transmitted, logged or stored. That matters here more than on most tools, since a date of birth is personal data that turns up in identity verification.
Related tools
- Date Calculator — add or subtract days, weeks and months from a date
- Business Days Calculator — count working days, skipping weekends
- Countdown to Date — a live countdown to something ahead
- Time Duration Calculator — the same idea for hours and minutes
