This guide covers How to Calculate Your Age | TimeFlow — what it means, how it works, and how to use it. The explanations below are followed by worked examples with real dates and real times, a set of frequently asked questions, and links to the tools that do the calculation for you: the time zone converter, the world clock, and the UTC converter. Where a number is given — an offset, a date, a count — it is computed from the IANA Time Zone Database for the date stated, not copied from a table that may be out of date.

Try the tool: Time Zone Converter — convert any time between any two cities, with the daylight saving rules for the date you choose.

Your age is the time between your date of birth and today, expressed in years, months and days. The calculation is simple in principle and fiddly in practice, because months have different lengths and leap years exist.

The standard method is to count full years first. Take today's year minus your birth year; that is your age in years, unless your birthday has not happened yet this year, in which case subtract one. Then count the full months since your last birthday, and the days since the start of the current month. So a person born on 15 March 1990 is 36 years old on 11 November 2026, with 7 full months and 27 days since their last birthday.

The fiddly parts are the edges. If you were born on 29 February, your birthday in non-leap years is usually celebrated on 28 February or 1 March, and your legal age depends on the jurisdiction. If you were born on 31 January, your 'one month later' date in February does not exist, and calculators have to decide whether to use 28 February or 1 March. Different calculators handle these edges differently, which is why two age calculators can disagree by a day.

Age in total days, weeks and hours is easier: it is just the number of days between the two dates, multiplied out. A person born on 1 January 1990 has lived about 13,500 days by November 2026 — roughly 1.94 million minutes. The age calculator on this site does all of it for you, including the leap-year handling, and shows the result in years, months, days and total days.

In practice

The calculation is simple, but the edge cases are not. Your age in years is the current year minus your birth year, minus one if your birthday has not happened yet this year. The months and days are the same idea: count the full months since your last birthday, then the days since the start of this month. The age calculator does it exactly, including the leap days, and the date calculator works out any date difference.

The tricky case is a birthday on 29 February. Someone born on a leap day has a birthday only every four years, and the law differs by country: in the United Kingdom and Hong Kong, the birthday is legally 1 March in non-leap years; in the United States and New Zealand, it is 28 February. For everyday purposes, leap-day babies usually celebrate on 28 February or 1 March, and the exact age is the same either way.

Age is also a legal concept, not just a number. The age at which you can vote, drive, drink, marry and retire all differ by country, and they are all defined by the calendar: you become 18 at the start of your birthday, not at the end of it. The age calculator gives the exact figure, and the birthday countdown counts down to the next one.

The numbers: a worked example

Take someone born on 1 January 2000. On 11 November 2026 they are 26 years, 10 months and 10 days old — 9,811 days in total, or 1,401 weeks. They were born on a Saturday, their next birthday is on 1 January 2027 (a Friday), in 51 days, when they turn 27. They turned 18 in 2018, 21 in 2021, and will turn 30 in 2030 and 65 in 2065.

The calculation is simple once you see it done: count the full years first (2000 to 2026 is 26), then the full months since the last birthday (January to November is 10), then the days (1 November to 11 November is 10). The age calculator does it exactly for any date of birth, including the leap days, and the birthday countdown counts down to the next birthday live.

The milestones for someone born on 1 January 2000:

Milestone Year Status in 2026
18 2018 Turned 18 in 2018
21 2021 Turned 21 in 2021
30 2030 Will turn 30 in 2030
40 2040 Will turn 40 in 2040
50 2050 Will turn 50 in 2050
65 2065 Will turn 65 in 2065

They turned 18 in 2018 and 21 in 2021; the next milestone is 30, in 2030. The milestones that matter most in practice are 18 (voting and adulthood in most countries), 21 (drinking age in the United States), and 65 (retirement age and pension eligibility in many countries — though the exact age varies by country and by scheme).

Key facts

  • Your age in years is the current year minus your birth year, minus one if your birthday has not happened yet this year.
  • One day is 86,400 seconds; one year is about 31.5 million seconds.
  • Someone born on 29 February has a birthday only every four years.
  • The calendar repeats every 28 years in most cases, so your birthday falls on the same weekday again after 28 years.
  • The milestones that matter most are 18 (voting), 21 (drinking age in the US) and 65 (retirement in many countries).

Frequently asked questions

How do I calculate my age?

Subtract your birth year from the current year, then subtract one if your birthday has not happened yet this year. For months and days, count the full months since your last birthday, then the days.

How old am I if I was born on 1 January 2000?

26 years, 10 months and 10 days on 11 November 2026. The age calculator gives the exact figure for any date of birth.

What if I was born on 29 February?

You have a birthday only every four years. In the UK and Hong Kong it is legally 1 March in non-leap years; in the US and New Zealand it is 28 February.

How do I calculate my age in days?

Count the days from your date of birth to today, including the leap days. The age calculator shows the total days, weeks, hours and minutes.

When will I turn 18?

In your birth year plus 18. Someone born in 2008 turns 18 in 2026; someone born in 2010 turns 18 in 2028.

How many days has someone born on 1 January 2000 lived?

Count the days from 1 January 2000 to today, including the leap days — the age calculator gives the exact total, in days, weeks, hours and minutes.

What is the time difference between London and Tokyo?

Nine hours in January 2026: London is UTC+00:00 and Tokyo is UTC+09:00. In July it is eight hours, because London moves to UTC+01:00 while Tokyo stays on UTC+09:00. The time zone converter gives the difference for any two cities and any date.

Related pages

Sources

  • IANA Time Zone Database, via Node.js Intl (Intl.DateTimeFormat with timeZone) — offsets, daylight saving dates and local times in this article were worked out from the IANA database, not typed from memory.
  • TimeFlow's own time-zone data (data/cities.ts, data/dst.ts), computed from the IANA database.
  • Time zone rules and offsets: the IANA Time Zone Database, as applied by this site's tools. Offsets and daylight saving dates on this page are computed from the database for the dates stated.
  • TimeFlow's time zone converter, world clock and UTC converter — the live tools behind the numbers on this page.
  • Time-zone and daylight saving rules are set by governments and can change. For flights, deadlines and meetings that cannot move, confirm the time with an official source.