Age Calculator

Calculate age in years, months, and days from a date of birth. You can also find the length of time between two dates, reverse a recorded age into a birth date, or estimate a date of death from age at death.

What is my age?

Enter your date of birth and leave Find Age on as today to see your chronological age. Change the as-of date to learn how old you were, or will be, on another day. Days until the next birthday appear with every age result.

How old is my child?

Parents of newborns often speak in weeks or months. Enter the child’s birth date and Calculate. The result lists years, months, and days, plus total weeks and total days, so you can answer “how many weeks old” without a separate tool.

Calculate date of birth

Genealogy records sometimes give age on a census or marriage date instead of a birth date. Choose Date of Birth mode, enter that age, set the record date, and Calculate. If you already know the birth date and only need to add or subtract years, use the date calculator.

If you only know whole years, the answer is a one-year window. Years plus months and days produce a single calendar date.

Calculate date of death

When a document lists age at death but not the death day, choose Date of Death mode. Enter the birth date and the age at death. Full years-months-days give one date. Whole years alone return a date range for the lifespan end.

How this calculator calculates age

Age mode subtracts the birth calendar date from the as-of date using ordinary date arithmetic, with borrow rules when days or months would go negative. Reverse modes start from a known age and a reference date, then add or subtract that span on the Gregorian calendar.

How to calculate age by hand

One approach sums whole years as 365 or 366 days, then adds the leftover partial year. Another sets the dates up like long subtraction in year-month-day columns:

1. Put the later date on top and the earlier date underneath.
2. Subtract days. If you need to borrow, take one month and add that month’s day count (28–31) to the day column.
3. Subtract months. If needed, borrow one year (add 12 months).
4. Subtract years.

Example: age on March 10, 2026 for a November 15, 2006 birth. Days go from 10 to 38 after borrowing February’s 28 days, leaving 23 days. Months become 14 after borrowing a year, leaving 3 months. Years become 2025 − 2006 = 19. Result: 19 years, 3 months, 23 days.

Month ends can still look odd (Feb 28 vs Mar 31). This tool treats Feb 28 to Mar 28 as one month, then counts leftover days, which matches common age calculators.

How many days until a date?

You can reuse Age mode as a day counter: put today in Date of Birth and the event in Find Age on. Total days is the countdown. Manual counts need leap days and month lengths:

How to calculate age from a birthdate in Excel

Put the birth date in cell A1 (MM/DD/YYYY). Age in whole years:

=DATEDIF(A1, TODAY(), "Y")

Remaining months after those years: =DATEDIF(A1, TODAY(), "YM")

Remaining days: =DATEDIF(A1, TODAY(), "MD")

Combine with CONCAT if you want a single “years, months, days” string, the same shape this page shows under Age.

Leap years and February 29

Leap years add February 29 when the year is divisible by 4, except century years must be divisible by 400. For February 29 births, many civil systems use February 28 as the age-up day in non-leap years. The next-birthday line follows that practice.

FAQ

How do I find age on a past or future date?

Stay in Age mode, enter the birth date, set Find Age on to that day, then Calculate.

Why are hours and seconds marked approximate?

They multiply whole calendar days by 24, 1,440, and 86,400. They do not use the exact clock time of birth.

What if I only know age in years for genealogy?

Date of Birth mode still works. Whole-year ages return a birth-date range. Add months and days from the record when you have them for a single date.