How is exact age calculated from a date of birth?
Age is calculated by subtracting your birth date from today's date, accounting for leap years, varying month lengths, and whether your birthday has occurred yet this year. For example, a person born on 15 March 2000 turns 25 on 15 March 2025 — regardless of how many days have passed since 1 January 2025.
How do I calculate age between two specific dates?
Simply enter any start and end date to find the exact duration. This is useful for calculating the age of a child at a past or future milestone, finding out how long ago an event happened, or determining eligibility deadlines (e.g. age cut-offs for schools, sports, or benefits).
What is chronological age vs biological age?
Chronological age is simply the number of years since birth. Biological age reflects how old your body functions — it can be significantly lower or higher than your chronological age based on genetics, lifestyle, exercise, diet, sleep, and stress. Tests like telomere length measurement, grip strength, and VO2 Max can estimate biological age.
How do I calculate someone's age on a specific past or future date?
Use both the start (birth date) and end date fields. Enter the target date as the end date. This is useful for legal calculations — for example, determining whether someone was under 18 on the date of a contract — or working out how old you will be on a future birthday or anniversary.
Why does age calculation differ between countries?
Most countries calculate age Western-style: you are 0 at birth and gain a year on each birthday. Some East Asian countries (notably South Korea) have traditionally counted age differently — adding 1 at birth and adding another year each New Year's Day. South Korea officially standardised to the international system in 2023. This calculator uses the international (Western) standard.