What this calculator does
Enter a date of birth and the calculator gives the exact age today, written as whole years, months and days, for example 36 years, 4 months and 28 days for someone born on 15 May 1990 on 13 October 2026. Change the "age on" date to see the age at any other moment: on the first day of school, on a deadline in a contract, or on the day of an exam that has an age limit.
Under the main answer you get the next birthday with a countdown in days and the age that will be reached, the weekday of the birth, the Western zodiac sign, the Vietnamese zodiac animal with its Can Chi name, and the same age expressed as a total number of months, weeks, days and hours. The whole summary can be copied in one click.
How to use it
- Pick the date of birth. Any date from year 1 to 9999 is accepted.
- The age on date is today by default. Pick another date to calculate a past or future age, or press Today to return.
- Read the result. If the date of birth is 29 February, a third field lets you choose whether the birthday is kept on 28 February or 1 March in years without a leap day.
Nothing is sent anywhere: the calculation runs in your browser, and "today" is your device's own date.
How the exact age is counted
The calculator counts forward from the birth date in whole months, then counts the days that are left. Each monthly step is measured from the original birth date, never from the previous step, so the result does not drift at the end of a month.
- Month ends. When the birth day does not exist in a month, the step lands on the last day of that month. Someone born on 31 January is exactly 1 month old on 28 February (29 in a leap year), 1 month and 1 day old on 1 March, and 2 months old on 31 March. This is the same rule spreadsheets use for EDATE.
- Leap-day birthdays. A person born on 29 February has a real birthday only every four years. By default the calculator celebrates it on 28 February in the other years, so they are a year older at the end of February. Some laws use 1 March instead (England and Wales, for example, for coming of age); the option switches the rule and the countdown follows it.
- Totals. The age in days is simply the number of calendar days between the two dates. Weeks are whole weeks plus the remaining days. Hours are days × 24: a day with a daylight-saving change still counts as 24 hours, because the question is about calendar dates, not clock time.
The arithmetic uses plain calendar dates rather than clock times, so time zones and daylight saving cannot push the result a day out.
The zodiac sign and the Vietnamese zodiac animal
The Western sign uses the conventional dates (Aries from 21 March, Taurus from 20 April, and so on). The Sun actually crosses each boundary on a slightly different day each year, so if you were born on the first or last day of a sign, astrologers may place you in the neighbouring one.
The Vietnamese zodiac (con giáp) is worked out from the calendar year, which is an approximation. The lunar year begins at Tết, which falls between 21 January and 20 February, so anyone born in January or early February may belong to the previous year's animal. When that can happen the calculator says so and names the alternative. Vietnam uses the Cat (Mão) where the Chinese zodiac has the Rabbit. For an exact answer, look up the date of Tết in your birth year in a lunar calendar.
