Age Calculator guide
Enter a date of birth to get your exact age in years, months, and days, the total number of weeks and days you have been alive, and how many days remain until your next birthday. Change the second date to find someone's age on any past or future day.
How exact age is calculated
Age in years, months, and days is calendar math, not division. The calculator subtracts the birth year from today's year, then checks whether this year's birthday has happened yet. If it has not, it borrows a year and adds 12 months. If the day of the month has not arrived, it borrows a month and adds the number of days in the previous month.
That borrowing step matters because months have 28 to 31 days. Dividing total days by 365.25 gets close, but it can be off by a day around birthdays, which is exactly when people check.
Worked example
Born March 15, 1990, checked on January 10, 2026. Years: 2026 − 1990 = 36, but the March birthday has not happened, so 35. Days: 10 − 15 = −5, so borrow a month and add December's 31 days, giving 26 days. Months: January minus March is −2, minus the borrowed month is −3, plus 12 = 9. Result: 35 years, 9 months, 26 days.
Total days lived is simpler. Someone born January 1, 2000 is exactly 26 years old on January 1, 2026. That is 26 × 365 = 9,490 days plus 7 leap days (2000, 2004, 2008, 2012, 2016, 2020, 2024) for 9,497 days.
Leap day birthdays
If you were born on February 29, your birthday exists only once every four years. For legal purposes, the answer depends on jurisdiction: some treat February 28 as the anniversary in common years, others March 1. For everyday age math, this calculator counts February 28 as your birthday in a non-leap year, so you turn a year older on the 28th, not March 1.
Note that 1900 was not a leap year and 2100 will not be one. Century years are leap years only if divisible by 400, which is why 2000 was.
Ages that matter in the US
18: voting, contracts, and most legal adulthood. 21: alcohol purchase in every state. 25: typical age when car rental surcharges drop. 26: the last year you can stay on a parent's health plan under the ACA. 59½: penalty-free withdrawals from IRAs and 401(k)s. 62: earliest Social Security retirement benefits. 65: Medicare eligibility. 67: full Social Security retirement age for anyone born in 1960 or later. 73: required minimum distributions begin for most retirement accounts under current law.
Half-year thresholds like 59½ are where exact month-and-day age is useful. The IRS counts 59½ from six calendar months after your 59th birthday.
Age in other units
Sometimes you need age in a single unit. In months: multiply full years by 12 and add the extra months. A child who is 2 years, 4 months old is 28 months old, which is how pediatricians track milestones until about age 3. In weeks: total days ÷ 7. In hours: total days × 24. A 30-year-old has lived roughly 262,800 hours.
For fun milestones, 10,000 days arrives at about 27 years and 4 months. One billion seconds arrives at about 31 years and 8 months.
Time zones and the day you were born
Age calculators work in calendar dates, so the time zone you were born in usually does not matter. It can matter at the edges: someone born at 11 p.m. on December 31 in California was born on January 1 in UTC. Legal documents always use the local date on your birth certificate, and so does this calculator.
The same logic applies to deadlines. If a form says you must be 18 "on or before" a date, compare your birth date to that date directly rather than counting days. The calendar method handles month lengths and leap years for you.
Other uses
People use exact age for school enrollment cut-off dates, sports age groups, visa and passport forms, pet ages, and counting down to milestones. For the gap between any two arbitrary dates, the days-between-dates calculator is the better fit. Your birth date stays in the browser and is not stored.
Frequently asked questions
How do you calculate exact age?
Count whole years since the birth date, then whole months since the last birthday, then the remaining days. Someone born June 15, 1990 is 36 years, 3 months, and 10 days old on September 25, 2026.
How old will I be on a specific date?
Change the 'Age on this date' field to any future or past date. That answers questions like how old you will be at a wedding, a retirement date, or the start of a school year.
How many weeks old am I?
Divide your age in days by 7. The calculator shows total weeks directly; a 36-year-old has lived roughly 1,890 weeks.
How is age calculated for a February 29 birthday?
In non-leap years this calculator counts February 28 as the birthday, so a leap-day baby turns a year older on the 28th. Legal conventions vary by jurisdiction, and some use March 1.
Why do some age calculators differ by a day?
The difference comes from month ends. Going from January 31 to the end of February, some tools overflow into March. This one clamps to the last day of the month, so January 31 plus one month is February 28 (or 29).
Does the time zone I was born in matter?
Only for the exact hour. Age in years, months, and days uses calendar dates, so the result is the same wherever you are unless you were born within a few hours of midnight in another time zone.
Is my birth date stored or uploaded?
Everything runs in your browser. Nothing you enter is uploaded to a server or stored by us.
How many days old am I?
Multiply full years by 365 and add one day for each February 29 you have lived through, then add the days since your last birthday. The calculator does this automatically.
When is someone legally 59 and a half?
Six calendar months after their 59th birthday. Someone born March 10, 1967 reached 59½ on September 10, 2026.