Birth Date Age Calculator
Any birth date works, including February 29.
A birth date age calculator turns any date of birth into an exact age using calendar borrowing: years, months, and days counted on the real calendar. June 15, 1990 to October 5, 2026 is 36 years, 3 months, and 20 days, a Friday birth, 13,261 days lived. February 29 birthdays count from March 1 in non-leap years by convention.
How the date math works
The calculator validates the birth date first, rejecting impossible dates like February 30, then subtracts with borrowing: negative days borrow the previous month's actual length, negative months borrow a year.
This beats the common shortcut of dividing day counts by 365.25, which drifts by days over a lifetime and cannot produce exact months.
Leap-day birthdays
Born February 29? In non-leap years the standard convention counts your birthday as March 1 for age math, keeping the years-months-days sequence unbroken.
Some people celebrate on February 28 instead, which is a fine party choice, but the calendar math uses March 1 so the age increments correctly.
Practical uses
Age-in-months matters for infant milestones and some school cutoffs. Total days lived shows up on insurance and legal forms. Birth weekdays settle family trivia debates.
For genealogy, run the same math backward: given an age at death and a death date, you can narrow the birth date to a small window.
Skip the arithmetic
Enter any birth date and get the exact age.
Birth date age questions
How do you calculate age from date of birth?
Subtract birth year, month, and day from today's date. Borrow the previous month's days when the day goes negative and 12 months when the month goes negative. The calculator does this on the real calendar instantly.
What if someone was born on February 29?
By convention, February 29 birthdays age from March 1 in non-leap years. This keeps the years-months-days arithmetic consistent across the whole calendar.
Can I calculate someone else's age?
Yes. Enter any birth date and the calculator returns the exact age, days lived, birth weekday, and next-birthday countdown for that person.