Age Calculator

How to use this tool

1. Enter your birthdate. Pick your date of birth from the date input. It defaults to a common example; replace it with your own date.
2. Set the reference date. The "Age at" field defaults to today. Change it to calculate your age at any past or future point.
3. Read the results. Your calendar age appears with total days, weeks, clock totals, next birthday countdown, and the day of the week you were born. Add a birth time to calculate elapsed clock totals.

How age is calculated

Age is measured by counting complete calendar years, then complete calendar months, then remaining days. This matches how age is commonly stated: a person born on January 31 who turns 30 on March 1 is "30 years, 0 months, and 28 (or 29) days old," not 30 years and 30 days, because the intervening month of February has fewer than 31 days.

The "days" component is the number of days elapsed since the last complete-month anniversary of the birthdate. It depends on which month that anniversary falls in, so the same elapsed time can show different day counts depending on when the year boundary lands.

You can also add a birth time to calculate elapsed clock hours, minutes, and seconds. For a reference date other than today, enter the time to compare against; for today, the calculator can use your current local time. Without a birth time, the clock totals assume birth at local midnight, so they are estimates. Both times are interpreted in your device's time zone, and daylight-saving changes or a birth in a different time zone can affect the result. The calendar years, months, and days remain date-based either way.

Leap year birthdays (February 29)

About 1 in 1,461 people are born on February 29. In most legal systems and everyday convention, the birthday is observed on February 28 in non-leap years. A minority of jurisdictions (notably parts of the UK and some US states for legal age thresholds) use March 1 instead. This calculator uses February 28 and displays a note on the result so you can adjust if your situation calls for the March 1 convention.

Zodiac signs

Western (tropical) zodiac signs are determined by fixed calendar cutoffs derived from the position of the sun at the spring equinox. The cutoff dates shift by ±1 day over the 400-year Gregorian cycle due to leap year insertion. If you were born within a day of a cusp (the boundary between two signs), the exact sign depends on your birth time and location; check both signs or use an ephemeris for precision.

Chinese zodiac is assigned by year. The traditional system uses the lunar new year as the boundary, which typically falls between January 21 and February 20. This calculator uses the Gregorian calendar year as a close approximation. If you were born in January or early February, the sign shown may differ from the traditional assignment based on the exact lunar new year date for your birth year.

Milestone ages

Age in different cultures

Not all cultures count age the same way. In the traditional Japanese kazoedoshi system, a person is considered 1 year old at birth and gains a year on New Year's Day rather than on their birthday - so someone born on December 31 is 2 years old two days after birth. Korea historically used a similar counting system (goryeonnai), where everyone ages one year on January 1st. South Korea officially moved to the international (Western) age system in June 2023. In most Western countries, age 0 begins at birth and a person turns 1 exactly one year later.