π Age Calculator
Find your exact age and days until your next birthday.
Age
How to Use This Tool
Enter your date of birth and choose a reference date (defaults to today). The calculator shows your exact age in years, months, and days, plus total days and weeks lived, the day of the week you were born, and how many days until your next birthday.
Enter your date of birth in the Date of Birth field using the date picker.
The Age on Date field defaults to today. Change it to calculate your age on any past or future date.
Click Calculate Age to see the full results.
Read the detail breakdown: total days, weeks, months, the day you were born, and your next birthday countdown.
How Exact Age Calculation Works
Age is not simply the year difference between two dates. The calculation has to account for whether the birthday has already occurred in the current year, and that months have different lengths. The standard approach compares the year, month, and day components separately. Start by subtracting the birth year from the reference year. Then check if the birth month and day have passed in the reference year: if the reference date is January 15 and the birthday is March 10, the birthday has not occurred yet this year, so subtract one from the year count and add 12 months to the month difference. Days are then the difference in day-of-month, borrowing from the previous month if the day difference is negative. This produces the exact years, months, and days format: "25 years, 3 months, 7 days." Total days lived comes from dividing the millisecond difference between dates by 86,400,000. That number accounts for leap years automatically since JavaScript's Date object represents dates as UTC milliseconds. The day of the week is derived from the Date object's getDay() method, which internally uses the Doomsday algorithm or equivalent.
Common Use Cases
Frequently Asked Questions
How is exact age calculated?
Age is calculated by comparing year, month, and day of the birthdate to today. Months and days are adjusted if the birthday hasn't occurred yet this year.
What is my age in days?
Multiply years Γ 365.2425 (accounts for leap years) and add remaining months and days. Our calculator shows the precise total.
How many days until my next birthday?
We calculate the next occurrence of your birth month and day, then subtract today's date to get the exact day count.
What is a half-birthday?
A half-birthday is exactly 6 months after your birthday. Some people celebrate it, and in some schools it's used for children with summer birthdays.
What day of the week was I born?
Our calculator determines this using the Zeller's congruence algorithm applied to your date of birth.