Answerivo

Dates & Time

Age Calculator

Age looks simple until leap years and short months get involved. Enter a date of birth — and any date you want to measure to — for an exact age in years, months, and days, along with the countdown to the next birthday.

Step 1

Enter your numbers

Use the date picker or type yyyy-mm-dd.

Defaults to today. Change it to work out an age on any date.

Results update as you type. Nothing you enter leaves your device.

Step 2

Results

Fill in the form and your results appear here instantly.

Estimates only. Verify important figures against your own records before acting on them. See our disclaimer.

What this calculator includes

What you enter

  • Date of birth
  • Age as of

What you get back

  • Age
  • Age in years
  • Days until the next birthday
  • Total days lived
  • Total months
  • Total weeks
  • Total hours

How this calculation works

How this calculation works

Age is counted in calendar units, not by dividing days by 365. Years advance on the birthday, and when the day of the month has not been reached yet, days are borrowed from the previous month — which is what makes leap years and 30-day months behave correctly.

  • Years = target year − birth year, months = target month − birth month, days = target day − birth day
  • If days is negative, borrow the length of the birth month and reduce months by one
  • If months is negative, add 12 and reduce years by one
  • Total days lived = (target date − birth date) ÷ one day
  • Next birthday = the birth month and day in the current year, rolled forward a year if it has already passed

What the result means

Age is counted in calendar units, not by dividing days by 365, so leap years and short months come out right. Total days lived is the exact elapsed day count between the two dates.

Common mistakes and assumptions

  • Dividing total days by 365 and expecting the same answer.
  • Entering a birth date after the target date.
  • Expecting time zones to matter — dates are compared as calendar dates.

Worked example

Someone born on 14 March 1990, measured as of 4 September 2026.

  1. 1Years = 2026 − 1990 = 36, months = 9 − 3 = 6, days = 4 − 14 = −10.
  2. 2Days is negative, so borrow the 31 days of the starting month (March): days = 21 and months drops to 5.
  3. 3Age = 36 years, 5 months, 21 days.
  4. 4Total days lived = 13,323, which is 1,903 complete weeks.
  5. 5The next birthday is 14 March 2027, which is 191 days away.

Frequently asked questions

Why not just divide the days by 365?
Because leap years make that drift. Over 40 years the shortcut is off by around ten days, and it can put you on the wrong side of a birthday.
How are people born on 29 February handled?
In non-leap years the browser's date field will not accept 29 February, and the age rolls over on 1 March in the day count. Legal treatment varies by jurisdiction.
Can I calculate an age in the past?
Yes. Change the "Age as of" date to any date after the birth date — useful for eligibility cut-offs and school year dates.
Does time of day matter?
No. Everything is measured in whole calendar days, so the result is the same regardless of the hour of birth.

Disclaimer

This calculator returns estimates based only on the values you enter. It does not account for taxes, financing terms, local regulations, or conditions specific to your operation, and it is not accounting, legal, tax, or investment advice. Confirm any figure that carries real cost before you rely on it.

Calculations run entirely in your browser and the numbers you type are never sent to us or stored. Read how Answerivo calculators are built.

Formulas and worked example last reviewed .