Time & Date · Date Math
Age Calculator
Calculate exact age from a date of birth — in years, months and days, and in total months, weeks and days — on today's date or any other date, with a countdown to the next birthday and the weekday you were born.
A ready-made version of the Date Difference Calculator.
How this is calculated
Years, months, days: step whole months from the earlier date (clamping to month ends), then count the remaining days
- Working days
- Days from the start (inclusive) to the end (exclusive) that aren't weekend days or listed holidays; negative if the end is earlier
- Include end date
- Adds one day so both the start and end dates count
The years-months-days answer walks the calendar month by month from the earlier date, so it reflects real month lengths rather than a 30-day average — 31 January to 29 February 2024 is exactly 1 month. Total days count the gap between the dates (1 to 3 March is 2 days); switch on 'include the end date' to count both ends. If the end date is before the start date, every figure is shown as negative.
Assumptions & sources
- Dates are whole calendar days in one time zone; hours and minutes are whole days × 24 × 60.
- Working days use your weekend setting (Saturday–Sunday by default) and the holidays you list.
- 1ISO 8601 — Date and time format (week numbering, calendar dates) — International Organization for Standardization
- 2Calendrical Calculations (Reingold & Dershowitz) — Cambridge University Press
Calculator ID TIME-DATEDIFF-001/age · version 2.0.0
Common questions
How is exact age calculated?
Whole years since the date of birth, then whole months since the last birthday, then the remaining days — the same way you'd count on a calendar.
How do I find my age on a specific date?
Change 'Age on This Date' — for example to an exam's or job's age cut-off date.
When do people born on 29 February celebrate?
In common years this calculator counts the birthday on 28 February. Legal age in some countries is counted from 1 March instead.