Age Calculator
Calculate age in completed years, months and days for any explicit comparison date, with exact elapsed days and the next birthday shown.
Inputs
Try an example
Result
Enter your values and press Calculate to see the result here.
Frequently asked questions
How does the calculator work out my age?
It counts birthdays completed by the comparison date, matching the CDC definition of age at last birthday. It then counts whole calendar months from the last birthday and the exact days left over. Total days are found independently by subtracting Gregorian day numbers.
Why do I enter a comparison date instead of using today automatically?
An explicit comparison date makes the result reproducible. It is stored in the GET URL, so opening the link later gives the same answer rather than silently reading a new date from the device clock. You can still enter today when that is the date you need.
How are 29 February birthdays handled?
In a leap year the anniversary is 29 February. In a common year this calculator uses 1 March, the convention stated in section 6 of the Age of Legal Capacity (Scotland) Act 1991. Rules for a particular jurisdiction or program may differ, so check the rule that governs your decision.
Can this result prove that I have reached a legal age?
No. It uses the popular anniversary method for a general calendar result. 42 CFR 436.522 itself distinguishes that method from a common-law method that reaches an age one day earlier, and applicable rules can vary. Use the responsible agency’s definition for eligibility, contracts or deadlines.
Can a timezone change the answer?
No. Both inputs are civil dates with no time of day or timezone. The calculation counts calendar midnights between those dates, so it cannot move a birthday backward or forward when the server, browser or person is in a different timezone.
Sources
- Age — Health, United States: Sources and Definitions — Centers for Disease Control and Prevention, National Center for Health Statistics, retrieved 2026-08-15
- 42 CFR § 436.522 — Determination of age (2025 annual edition) — U.S. Government Publishing Office, retrieved 2026-08-15
- Age of Legal Capacity (Scotland) Act 1991, section 6 — The National Archives, legislation.gov.uk, retrieved 2026-08-15
- Leap Years — U.S. Naval Observatory, Astronomical Applications Department, retrieved 2026-08-15