Age Calculator: Exact Age in Years, Months and Days
An age calculator finds the exact time between a birth date and today, expressed in years, months and days — and in total days, weeks and hours. It handles month lengths and leap years, which is where manual arithmetic usually goes wrong.
How exact age is worked out
The calculation subtracts calendar components and borrows where needed: if the current day is earlier in the month than the birth day, it borrows days from the previous month, then adjusts months and years. Because months vary between 28 and 31 days, the number of days borrowed depends on which month you are in.
Leap years and 29 February
A leap year occurs every four years, except century years not divisible by 400 — 1900 was not a leap year, 2000 was. People born on 29 February usually observe their birthday on 28 February or 1 March in common years, and most legal systems treat 1 March as the date a legal age is reached.
Where exact age is needed
- Legal thresholds: driving, voting, alcohol, retirement and pension eligibility.
- Medical dosing and paediatric growth charts, which use age in months.
- Sports age-group eligibility, usually fixed on a cut-off date.
- Visa, insurance and school entry rules that depend on age on a specific day.
Key takeaways — Age Calculator
- Exact age accounts for varying month lengths and leap days.
- Total days and weeks are useful for infant and medical contexts.
- Some official systems count age differently — check the rule that applies.