Age Calculator

Age is counted the way a calendar counts: full years up to the last birthday, then full months, then the remaining days. Born on 15 May 1990, on 29 September 2026 you are 36 years, 4 months and 14 days old — 36 years to 15 May 2026, four months to 15 September, and 14 days more. Months are counted on the day of the month of the birth, and when a month is too short the last day of that month is used, as date libraries do. The totals in months, weeks, days, hours, minutes and seconds come from the exact distance between the two dates, and they tick every second when you calculate the age right now.

People born on 29 February have a birthday only every four years, and the rule for the other years is a convention, not a fact. In the United Kingdom and Hong Kong the law treats 1 March as the day a “leapling” comes of age; New Zealand and Taiwan use 28 February. The calculator lets you choose and defaults to 1 March. All times are wall-clock times: the calculation does not know the time zone of the birth or the daylight-saving changes since then, so with a time of birth the hours are right to within an hour or so, and without one the age is counted from midnight.

The milestones are round numbers that are easy to miss: you are 10,000 days old at 27 years and about 4½ months, and one billion seconds old at about 31 years and 8 months. The zodiac sign uses the customary dates; the true boundary moves by a day between years, so check an ephemeris if you were born on the first or last day of a sign. The Chinese zodiac animal follows the Chinese calendar, whose year begins at Lunar New Year between 21 January and 20 February — someone born on 20 January 1990 is a Snake, not a Horse.