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 13,241 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.
Second worked example: when borrowing kicks in
Now a case where both borrows fire. Someone born on July 20, 1995 wants their age as of July 7, 2026. Days first: 7 minus 20 is negative, so borrow the length of the previous month (June has 30 days) to get 7 − 20 + 30 = 17 days, and knock one off the month count. Months next: 7 − 7 − 1 = −1, negative again, so borrow 12 months and knock one off the years, leaving 11 months. Years last: 2026 − 1995 − 1 = 30. Exact age: 30 years, 11 months, 17 days. That is 30 × 12 + 11 = 371 total months and 11,310 total days, with the next birthday on July 20, 2026, just 13 days away, turning 31. Two weeks later the same math collapses to a clean 31 years, 0 months, 0 days.
Milestone birthdays by birth year
Milestone math is simple addition: birth year plus the milestone age gives the calendar year, and the milestone lands on your birthday within it. The columns track the big US legal gates: adulthood and voting at 18, alcohol at 21, and Medicare eligibility at 65. Someone born in 2008 turns 18 on their 2026 birthday, which is why that cohort is registering to vote this year.
| Born in | Turns 18 | Turns 21 | Turns 30 | Turns 65 |
|---|---|---|---|---|
| 1960 | 1978 | 1981 | 1990 | 2025 |
| 1970 | 1988 | 1991 | 2000 | 2035 |
| 1980 | 1998 | 2001 | 2010 | 2045 |
| 1990 | 2008 | 2011 | 2020 | 2055 |
| 2000 | 2018 | 2021 | 2030 | 2065 |
| 2008 | 2026 | 2029 | 2038 | 2073 |
For a birth year not in the table, add the milestone age to it directly. One quirk: a February 29 baby keeps the same milestone years, but in common years the party lands on February 28 or March 1 by convention rather than on the literal date.
Leap years and month lengths
Two calendar quirks make naive age math drift. First, leap years: 2024 had a February 29 and 2028 will have one, so any span of years mixes 365-day and 366-day years. That is why age in days never stays equal to years × 365 for long, and why this tool counts real elapsed days instead of multiplying. Second, month lengths: when the day subtraction goes negative, the calculator borrows the actual length of the previous month, which can be 28, 29, 30 or 31 days depending on the month and the year. Between February 28 and March 1 there are two days in a leap year but only one in a common year like 2026, and the borrow logic tracks that automatically.
The one date that needs a convention rather than arithmetic is a February 29 birthday in a common year. This tool uses the March 1 convention for the birthday countdown, covered in the FAQ below, while the elapsed years, months and days stay exact either way.
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.
How old is someone born in 2000?
On their 2026 birthday they turn 26, so they are currently 26 if that birthday has already passed this year and 25 if it has not. The quick rule for any birth year: subtract it from the current year, then subtract one more if the birthday is still ahead. Enter the exact date above and the tool settles it to the day, including the months-and-days remainder.
Why isn't my age in days just years times 365?
Because leap years add an extra day roughly every four years. Someone born on July 20, 1995 completes 30 years on July 20, 2025, and that span is 10,958 days rather than 30 × 365 = 10,950 because it contains 8 leap days. This calculator counts real elapsed days, so the total-days row already includes every February 29 you have lived through.