How the age calculator works
Enter a date of birth and the date on which you want the age, today by default. The calculator counts the full years, then the full months since the last birthday, then the remaining days, the way people state their age in everyday life. It also gives the age in months, weeks and days, the number of days until the next birthday and the weekday it falls on.
The method
- Months: count the calendar months from the birth date to the reference date, minus one if the day of the month has not been reached yet.
- Years and months: divide that count by 12; the quotient is the age in years and the remainder the extra months.
- Days: count the days from the last “monthly birthday” to the reference date.
- Totals: the age in days is the plain difference between the two dates, leap days included.
Worked example
Someone born on June 15, 1990, on November 3, 2026:
- From June 15, 1990 to October 15, 2026 there are 436 full months.
- 436 ÷ 12 = 36 years, remainder 4 months.
- From October 15 to November 3, 2026: 19 days.
- Age: 36 years, 4 months and 19 days, or 13,290 days.
- The next birthday, June 15, 2027, is a Tuesday, 224 days away.
Age milestones
| Milestone | Reached at about |
|---|---|
| 1,000 days | 2 years 9 months |
| 5,000 days | 13 years 8 months |
| 10,000 days | 27 years 4 months |
| 1,000 weeks | 19 years 2 months |
| 1 billion seconds | 31 years 8 months |
| 20,000 days | 54 years 9 months |
Ages that matter in the US
Many rules depend on exact age: 16 for a driver’s license in most states, 18 to vote, 21 to buy alcohol, 59½ to withdraw from an IRA or 401(k) without the early-withdrawal penalty, 62 for the earliest Social Security benefits, 65 for Medicare, and 67 for full Social Security retirement age if you were born in 1960 or later. Changing the reference date shows exactly when you will reach each of them.
Birthdays on February 29
People born on a leap day have a real birthday only every four years. In other years, the calculator places the birthday on March 1, which is how it counts the next birthday. Celebrations often happen on February 28 instead.
Why years have different lengths
Because of leap years, a year is 365 or 366 days, and months range from 28 to 31 days. That is why an age in days divided by 365 does not give the exact age in years: the calculator counts calendar months instead.