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ToolMoose

Age Calculator

Find your exact age in years, months, and days from any date of birth.

Defaults to today. Change it to find an age on any date.

Age

Enter a date of birth to begin.

Worked examples

Born 1990-06-15, age today
On 2026-07-01 that is 36 years, 0 months, and 16 days, which is 432 total months.
Days until a birthday
A birthday on March 3 viewed from July 1 is 245 days away, counted from the age-at date.

How age is calculated

Your age is the gap between your date of birth and a target date, expressed as whole years, months, and days. Getting it right means respecting that months have different lengths, so a plain subtraction is not enough. The calculator works from the largest unit down, borrowing where a piece comes out negative.

Borrowing days, then months

We start by lining up the two dates and subtracting each part on its own: day minus day, month minus month, year minus year.

  • Days: if the target day of the month is smaller than the birth day, the day difference is negative. We borrow one month by adding the number of days in the month just before the target month, then subtract one from the month count. Because we use the real length of that specific month (28, 29, 30, or 31 days), the result stays calendar-correct.
  • Months: after the day borrow, the month count might be negative. We add twelve months and subtract one year.

What is left is your exact age. For example, someone born on the 31st viewed from a date early in a 30-day month will have days borrowed from the shorter month, which is why the day figure lands where it does.

Leap years

Leap years take care of themselves here. The day borrow uses the actual length of each month for its year, so February contributes 29 days in a leap year and 28 otherwise. The total-days and total-hours figures are computed from the raw millisecond difference between the two dates and then floored, so every leap day that falls in the range is counted.

Why it differs from year subtraction

A common shortcut is to subtract birth year from the current year. That only matches your real age once this year’s birthday has passed. Before that day, the shortcut is one year too high. This tool compares the month and day as well, so it reports the birthdays you have genuinely reached.

Totals and next birthday

Alongside the exact age we show totals: months, weeks, days, and hours across the whole span. The next birthday line finds the next time your birth month and day occur on or after the age-at date and counts the days remaining. If you were born on February 29, a non-leap year uses February 28 so the countdown still makes sense.

Frequently asked questions

How is exact age calculated?
We subtract the date of birth from the target date one unit at a time. First we compare the day of the month: if the target day is smaller, we borrow the length of the previous month and reduce the month count by one. Then we compare months: if that count is negative, we borrow twelve months and reduce the year count by one. What remains is your exact age in whole years, months, and days.
How are leap years handled?
Because we borrow the real length of each calendar month (28, 29, 30, or 31 days) and use actual month lengths for a given year, February's leap day is accounted for automatically. Total days and hours come from the true millisecond difference between the two dates, so leap days are always included in those figures.
Why does my age differ from simply subtracting the years?
Subtracting birth year from the current year only works if your birthday has already passed this year. If it has not, that method overstates your age by one year. The calculator checks the month and day too, so it reports the number of birthdays you have actually reached.
How does the days until birthday count work?
We take the month and day of your birth and find the next time that date occurs on or after the age-at date, then count the days between. If your birthday is February 29 and the next year is not a leap year, we treat February 28 as the birthday so the count stays sensible.

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Last updated: 2026-07-01