How do I calculate my age in days?

Enter your date of birth and leave the second date at today; the total-days line counts every calendar day since you were born, including leap days. Divide by 7 for weeks, which the calculator also shows with the remaining days.

What day of the week was I born on?

The calculator shows it under the result once a birth date is entered. It uses the Gregorian calendar, whose weekdays repeat exactly every 400 years because 146,097 days is a whole number of weeks.

When is my next birthday if I was born on 29 February?

In leap years it is 29 February. In other years this calculator uses 1 March, the first day on which a full year has passed; the countdown and the age you will turn follow that date.

Why was Korean age different from the age in my passport?

Traditional Korean age started at one and increased every 1 January, so it was one or two years higher than the international age. Since 28 June 2023 South Korean law uses the international age for official purposes, matching this calculator.

Can I calculate someone's age on a past date?

Yes. Change the Age on field to any date after the birth date. The calculator shows the exact age on that day, the totals up to it and the next birthday after it.

Age Calculator

Find an exact age from a date of birth: years, months and days, the total number of days and weeks lived, how long until the next birthday and which day of the week the birth fell on. Change the second date to get the age on any other day.

Date of birth

Age on

Leave “Age on” at today, or set any other date to find the age on that day. People born on 29 February have their birthday on 1 March in common years here.

Enter a date of birth to see the exact age.

How the exact age is worked out

The calculator counts whole years first, then whole calendar months, then the days that remain, the same way you would on a paper calendar. Someone born on 15 March 1990 is 36 years, 7 months and 3 days old on 18 October 2026. Total days and weeks are a straight count of calendar days from the birth date to the chosen date, so leap days are included automatically.

The result is in completed units: a person is not 37 until the birthday itself. Set the Age on field to a past or future date to answer questions like "How old was I when I started school?" or "How old will I be on the wedding day?". Ten thousand days, a popular milestone, arrives at about 27 years and 4½ months.

Birthdays on 29 February

About one person in 1,461 is born on a leap day, because 29 February appears once in every four-year cycle of 1,461 days. In common years this calculator moves the birthday to 1 March, which is when a full year has passed since 28 February. Legal rules differ: Hong Kong law, for example, says a leap-day baby reaches a given age on 1 March in common years, while some other jurisdictions use 28 February. Check the rule that applies when a birthday decides eligibility for a licence, a pension or a contract.

Leap years follow the Gregorian rule: every fourth year, but not century years unless they divide by 400. That is why the year 2000 had a 29 February and 2100 will not.

Milestone ages and when they began

For someone who reaches each age today, October 18, 2026: the birth date and the days and weeks lived so far.

Age	Born on	Total days	Total weeks
1	October 18, 2025	365	52
5	October 18, 2021	1,826	260
10	October 18, 2016	3,652	521
13	October 18, 2013	4,748	678
16	October 18, 2010	5,844	834
18	October 18, 2008	6,574	939
21	October 18, 2005	7,670	1,095
25	October 18, 2001	9,131	1,304
30	October 18, 1996	10,957	1,565
40	October 18, 1986	14,610	2,087
50	October 18, 1976	18,262	2,608
60	October 18, 1966	21,915	3,130
65	October 18, 1961	23,741	3,391
70	October 18, 1956	25,567	3,652
80	October 18, 1946	29,220	4,174
90	October 18, 1936	32,872	4,696
100	October 18, 1926	36,525	5,217

Different ways of counting age

This tool uses the international method: you are zero at birth and gain a year on each birthday. Traditional East Asian reckoning counted a newborn as one year old and added a year every New Year, so a baby born in late December could be two years old within days. South Korea, the last country where that count was in everyday official use, switched all legal and administrative ages to the international method on 28 June 2023.

Calendars matter too. The dates here are Gregorian in ISO 8601 form (YYYY-MM-DD). If a birth was recorded under another calendar, or before a country adopted the Gregorian calendar (Britain and its colonies did so in 1752, Russia in 1918), convert the date first. To count the days between any two other events, use the days between dates calculator.

Frequently asked questions

How do I calculate my age in days?: Enter your date of birth and leave the second date at today; the total-days line counts every calendar day since you were born, including leap days. Divide by 7 for weeks, which the calculator also shows with the remaining days.
What day of the week was I born on?: The calculator shows it under the result once a birth date is entered. It uses the Gregorian calendar, whose weekdays repeat exactly every 400 years because 146,097 days is a whole number of weeks.
When is my next birthday if I was born on 29 February?: In leap years it is 29 February. In other years this calculator uses 1 March, the first day on which a full year has passed; the countdown and the age you will turn follow that date.
Why was Korean age different from the age in my passport?: Traditional Korean age started at one and increased every 1 January, so it was one or two years higher than the international age. Since 28 June 2023 South Korean law uses the international age for official purposes, matching this calculator.
Can I calculate someone's age on a past date?: Yes. Change the Age on field to any date after the birth date. The calculator shows the exact age on that day, the totals up to it and the next birthday after it.