How age is calculated
Your age is the number of complete years since your date of birth. The calculator then counts the complete months since your last birthday, and the remaining days. Every calendar date is counted exactly, including leap years.
Worked example: someone born on 15 March 1990 is 36 years, 7 months and 21 days old on 5 November 2026. That is 13,384 days, or 1,912 weeks.
Birthdays on 29 February
If you were born on 29 February, the calculator shows your birthday as 28 February in non-leap years. Legal rules differ: in England and Wales, for example, a person born on 29 February legally reaches a new age on 1 March in a non-leap year. Check the rule that applies to you for legal purposes.
Common uses
| Purpose | Why exact age matters |
|---|---|
| School entry | Cut-off dates decide the school year a child joins |
| Pensions and retirement | State pension age in the UK and Social Security full retirement age in the US depend on birth date |
| Driving and voting | Minimum ages apply from the exact birthday |
| Medical dosing | Some children's medicine doses depend on age in months |
Pro-tip: to find someone's age on a past or future date, such as the day a contract starts, change the "Age on this date" field.
Frequently asked questions
How do I calculate my exact age?
Count the complete years since your birth date, then the complete months since your last birthday, then the remaining days. The calculator does this for you.
How many days old am I?
Enter your date of birth and the calculator shows your age in total days, weeks, months and hours.
How is age counted for a 29 February birthday?
The calculator uses 28 February in non-leap years. Some legal systems, such as England and Wales, use 1 March instead.
Can I calculate age on a future date?
Yes. Change the "Age on this date" field to any date to see how old someone will be or was on that day.