Age calculator

What this age calculator does

Enter your date of birth and the page shows your current age in years, months, weeks, days, hours, minutes and seconds. The display updates every second. Below the headline year count, six cards show the rest of the units. Below that, a "next birthday" card tells you how many days until your next birthday and which weekday it falls on, along with the age you'll be turning.

Everything runs in your browser. The date you enter is never sent to a server.

How years, months and days are computed

Years, months and days respect the actual lengths of calendar months rather than rounding to 30.44 days per month. The algorithm: subtract the calendar year, month and day separately; if the day result goes negative, borrow from the month using the previous month's actual day count; if the month result goes negative, borrow from the year. The result is the same year-month-day breakdown that a human would write on a form.

For someone born on January 31, the day-of-month difference at the end of February is computed against February's day count (28 or 29), not a flat 30. The same rule applies to any month boundary.

Other units shown

Total months, total weeks, total days, total hours, total minutes and total seconds are computed by dividing the elapsed milliseconds by the appropriate unit. These are not the "remainder" within a year, but the absolute count from birth to now. The total-days figure, for example, is a useful "how many days have I been alive" number that people use for personal milestones (10,000 days alive, 25,000 days alive).

For a countdown to the day you'll reach a specific milestone, use our how-long-until tool with the milestone date.

Next birthday

The next-birthday card shows the date of your next birthday, the weekday it falls on, the number of days until then, and the age you'll be turning. The calculation uses your current local timezone, so the "days" figure is the count to your local midnight on your birthday.

If your birthday is today and the current time has already passed midnight, the next birthday is next year. If your birthday is February 29 (leap day) and the current year is not a leap year, the page picks February 28 as the celebration day, matching the most common civil convention.

Use cases

Personal milestones: 1,000 days, 10,000 days, exact age in months for a young child, exact age in weeks for a pregnancy. Bureaucratic forms that demand "age in years and months". Curiosity: how old is your dog in days, how old is your car in months, how long until your library card expires (if you'd entered the issue date in birth-date format).

For birthday-specific countdowns, our birthday countdown page reuses the main flip-clock to count down to your next birthday.

Privacy

Your date of birth is processed entirely in your browser. The value is not uploaded, not stored in localStorage, and not used by any analytics or advertising service on the page. If you close the tab, the value is gone.

Related calendar tools

For a countdown to a specific upcoming date, use our how-long-until tool. For weekday-anchored events, see the named weekday pages. For format conversion between 12-hour and 24-hour time, the converter handles the edge cases (12 AM is midnight, 12 PM is noon).

For pure interval timing rather than calendar-anchored ages, the stopwatch and timer are the right tools.

The math behind a year-month-day age

The naive way to compute age in years is to subtract birth year from current year, then subtract 1 if the month-day hasn't yet arrived this year. That gives the correct year count but leaves the months and days unaccounted for. To finish the job, you compute the difference in months separately (with a similar adjustment) and then the difference in days.

Where this gets fiddly is the day adjustment. If you're 30 years and -3 days old by raw subtraction, the right reading is "29 years, 11 months, and however many days are in last month". The page borrows the day count from the previous month, which gives a different answer for February (28 or 29) than for March (31). The algorithm matches the conventional way a human would write the age on a form.

Counting milestone days

Some people like to track milestone day counts: 1,000 days, 10,000 days, 25,000 days alive. A 30-year-old is somewhere around 11,000 days old. A 70-year-old is somewhere around 25,500. The "total days" cell on this page gives you the exact figure; the how-long-until tool lets you target the specific calendar date you'd reach the next round number.

For pure interval timing during a milestone event, the timer and stopwatch handle short-form measurements; for the long-form countdown to a birthday specifically, our birthday countdown page reuses the main flip-clock.

Why the seconds count is so much larger than you'd guess

A 30-year-old has lived a little under one billion seconds. A 70-year-old has lived around two billion. The figure looks startling because we don't usually count time in seconds, but it's a useful reminder of how rich a single day is: 86,400 seconds. Every breath, every conversation, every page-load happens inside that allotment.