Date & time
Age Calculator
Enter your date of birth to see your exact age in years, months and days, how many total months and days you have lived, and how long until your next birthday. The "age at" date defaults to today but you can set it to any date, which is handy for figuring out how old someone will be on a future wedding, graduation, or work-anniversary date. It's a quick way to check eligibility cutoffs that come up in the United States — turning 16 to get a driver's license, 18 to register to vote, 21 to buy alcohol, or 65 for Medicare — without counting on your fingers. Everything runs entirely in your browser, so no birthday or personal date ever leaves your device.
Your dates
Enter your date of birth
Ages count complete calendar units, so the day of birth is counted as day zero (you turn 1 on your first birthday).
How the age calculator works
The exact age is found by subtracting calendar parts and borrowing where needed: if the "as-of" day is earlier in the month than the birth day, we borrow the number of days in the previous month; if the month is earlier, we borrow 12 months from the year. This produces a true years / months / days breakdown that respects different month lengths and leap years.
Method
days = asofD − dobD (borrow days-in-prev-month if negative) months = asofM − dobM − borrow (borrow 12 if negative) years = asofY − dobY − borrowwhere: totalDays = (asof − dob) ÷ 86 400 000 ms totalMonths = years × 12 + months countdown = next-birthday − asof, in days
Notes & assumptions
- The "as-of" date defaults to today (from your browser) and can be set to any date on or after the birth date.
- Total months counts whole months only; the leftover days are shown separately in the exact age.
- Calculations are for general information only — verify before relying on them.
Worked example
Imagine someone born on March 15, 1990, and you want their exact age as of June 15, 2026. Start with the days: the as-of day (15) minus the birth day (15) is 0, so no borrowing is needed there. Next the months: June is month 6 and March is month 3, so 6 − 3 = 3 months. Finally the years: 2026 − 1990 = 36 years. That makes the exact age 36 years, 3 months, and 0 days. In total months that's 36 × 12 + 3 = 435 months, and the total days lived works out to roughly 13,242 days. Their next birthday falls on March 15, 2027, which is about 273 days away from June 15, 2026 — at which point they'll turn 37. Because the math borrows the correct number of days from the previous month and accounts for leap years, the breakdown stays accurate no matter which months are involved.
Frequently asked questions
How do I calculate my exact age?
Subtract your date of birth from today's date one unit at a time — days, then months, then years — borrowing where a part goes negative. For example, if today's day is earlier in the month than your birth day, borrow the number of days in the previous month and reduce the month count by one; if the month is earlier, borrow 12 months and reduce the year count by one. This calculator does that automatically and respects different month lengths and leap years, so the years/months/days result is exact.
How many days until my birthday?
Find your next birthday — that's your birth month and day in the current year, or next year if this year's has already passed — and count the days from today to that date. The tool shows this countdown automatically: enter your date of birth and read the "Countdown to next birthday" row. If your birthday is today, it shows a celebration message instead of a day count.
How is age in months counted?
Age in months counts only whole, completed months. You complete a month when the same day-of-month rolls around again, so a baby born on the 10th becomes one month old on the 10th of the following month. This calculator reports total months as full years times 12 plus the leftover whole months, and any extra days beyond that are shown separately in the exact age. Partial months are never rounded up.
Do you count the day of birth as day one?
No. Age counts complete units, so your day of birth is day zero — you are zero years old on the day you're born and turn 1 only after a full year has passed. The same logic applies to days and months: a unit isn't counted until it's fully elapsed. That's why a newborn is described in days or weeks rather than starting at "one."
How does the calculator handle leap-year (February 29) birthdays?
If you were born on February 29, that date only exists in leap years. In common years this calculator treats the birthday as falling on March 1 for the countdown, which is the most widely used U.S. convention. The years/months/days math still borrows the real number of days in each month, so the elapsed-time figures stay correct.