Age Calculator: Exact Age in Years, Months and Days

Your age is the number of birthdays you have already passed, not the difference between two years on a calendar. Enter your date of birth below and the calculator returns the exact age in years, months and days, along with the same span converted into months, weeks, days and hours.

Why subtracting the years gets it wrong

The shortcut everyone tries first is current year minus birth year. It is right for roughly half the population on any given day and wrong for the other half.

Take a birth date of November 20, 2000. On August 17, 2026 that person has lived 25 years, 8 months and 28 days. Plain subtraction says 26. The November birthday has not come around yet, so a whole year is being claimed three months early.

The calculator works in the order the calendar does:

1. Count the complete years from the birth date forward.
2. Drop one year if the birthday is still ahead in the current year.
3. Count the whole months left over, then the leftover days.

Leap years, and the February 29 birthday

A common year has 365 days, a leap year 366. The U.S. Naval Observatory states the rule plainly: years divisible by four are leap years, except centurial years that are not divisible by 400. That is why 1900 and 2100 are ordinary years while 2000 was a leap year.

The reason for the exception is that the seasonal cycle, the tropical year, runs about 365.2422 days. Adding a day every fourth year would average 365.25 and overshoot; skipping three leap days every 400 years brings the average calendar year to 365.2425, close enough that the calendar drifts a full day from the seasons only after some 3,300 years.

For a person born on February 29, none of this changes the arithmetic. The birth date is fixed, the day count runs across real calendar days, and the age advances by one every fourth year whether the celebration lands on February 28 or March 1.

The same age, measured in other units

Years are one reading of a distance between two dates. The other units answer different questions, and each has its own page:

• Age in days — the running total of days lived.
• Age in months — the unit pediatric care uses for young children.
• Age in hours — hours and minutes, updated to the current time.
• Years between two dates — any pair of dates, not just a birth date and today.
• Age difference between two people — the gap between two birth dates.

Not every tradition counts age the same way

American searches often turn up “Korean age,” and it is a genuinely different system rather than a rounding quirk. In the traditional count a newborn is one year old, and everyone gains a year together on January 1, which puts a person one or two years above the international figure depending on the birthday.

South Korea settled the confusion by statute: the amended General Act on Public Administration and Civil Act took effect on June 28, 2023, making the international count — zero at birth, one more year on each birthday — the standard for contracts, laws and ordinances. That international count is the one this calculator uses.

Curious what day of the year you were born into? Check the zodiac sign for a birth date, or start the countdown to the next birthday. This is a date arithmetic tool and is not a substitute for official records.