Age Calculator

What this tool does

Enter a date of birth and this calculator gives the completed age in years, months and days, along with the totals in months, weeks and days, the weekday you were born on and how long until the next birthday. It works from calendar dates rather than timestamps, which is why the day counts stay correct across daylight-saving changes and leap years. You can calculate an age on any date, not just today.

How to use this tool

1. 1

   Step 1: Enter the date of birth

   Use the date field or type the date directly. The date is treated as a plain calendar date, so no timezone shifts it by a day.

2. 2

   Step 2: Choose the date to measure to

   This defaults to today in your local calendar. Change it to work out an age on a past or future date — useful for eligibility cut-offs.

3. 3

   Step 3: Read the breakdown

   Completed years, months and days appear first, then total months, weeks and days, the birth weekday and the countdown to the next birthday.

Worked example

How calendar age is computed

Years, months and days are borrowed down in that order, exactly the way you would do it on paper. Totals are counted in whole calendar days, never by subtracting timestamps.

years  = target year − birth year
months = target month − birth month
days   = target day − birth day
if days < 0:   borrow the number of days in the month before the target month
if months < 0: borrow 12 months from the year count

• Total days is counted as a difference of calendar day numbers, so a clock change never adds or removes a day.
• A birth date after the target date is rejected rather than reported as a negative age.
• The weekday is derived from the calendar date itself, independent of your device timezone.

Why calendar age is not elapsed time divided by 365

Limitations and privacy

A date of birth is personal data, so it never leaves this page. It is not transmitted, not stored, and never included in any analytics event.

Frequently asked questions