How to use the age calculator
- Date of Birth: pick the day you were born.
- As of Date: leave it on today to get your current age, or pick any date from October 15, 1582 onward to see the age on that day, such as the cut-off date on a school or sports form.
- Read the Exact age line, then the totals, the next-birthday countdown and the zodiac, generation and weekday facts. Results update as you change either date.
How the age is worked out
The tool compares calendar dates, not clock times. It counts whole years up to your most recent birthday, then whole months from that birthday, and the leftover is days. If a month is too short for your birth day (born on the 31st, counting through a 30-day month), the month ends on its last day. Total days is the difference between two day numbers on the Gregorian calendar, using Howard Hinnant's civil-date algorithms, and the weekday comes from the same number. Zodiac dates follow the commonly published table (Aries starts March 21), and the Chinese zodiac uses Lunar New Year dates from the Hong Kong Observatory conversion table. Generations follow Pew Research Center through 2012. Pew names no later group, so the tool continues with Alpha for 2013 to 2024 and Beta from 2025, names coined by McCrindle.
Worked example
With the sample birth date, May 15, 1990, and the As of Date on today (October 11, 2026), the tool shows 36 years, 4 months, 26 days. That is 13,298 total days, 1,899 weeks and 436 months. The next birthday is 216 days away, and the birth date was a Tuesday.
Limits and edge cases
- Dates before October 15, 1582 are not accepted, because the Gregorian calendar did not exist before then. A date of birth after the As of Date shows a message instead of an age.
- Time of birth and time zones are ignored.
- The Chinese zodiac uses the real Lunar New Year date for 1900 to 2100. For birth years outside that range it uses the calendar year and says so.
- Sign dates shift by a day between years, so a birthday on the edge of a sign can differ between websites.
- For the days between any two dates, use the date difference calculator, or count down to a party with countdown to date.
Frequently asked questions
How do I calculate my age from my date of birth?
Count the whole years since your last birthday, then the whole months since that birthday, then the leftover days. Typing a date of birth and leaving the As of Date on today does all three steps at once and also gives the total number of days you have lived.
How old is someone born on February 29?
This calculator counts the birthday of a leap-day baby as March 1 in years that are not leap years. For a birth date of February 29, 2000, the tool shows 24 years, 11 months, 30 days on February 28, 2025, and 25 years, 0 months, 0 days on March 1, 2025. Some places use February 28 instead, so check the rule on your form.
How many days old am I?
The Total Days card shows the number of calendar days from your date of birth to the As of Date. Someone born yesterday is 1 day old, and the birth date itself is not counted twice.
Why is my Chinese zodiac animal not the one for my birth year?
The Chinese zodiac follows the lunar calendar, and the animal changes at Lunar New Year, which falls between January 21 and February 20. Someone born on January 15, 1990 is a Snake, because Lunar New Year that year was January 27, so the Horse year had not started yet.
Can I find my age on a past or future date?
Yes. Change the As of Date to any date from October 15, 1582 onward. Use a past date to check an age at an event, or a future date to see how old you will be on the day a form, exam or milestone falls.