How Old Am I? How to Calculate Your Exact Age in Years, Months & Days
“How old am I?” sounds like the easiest question in the world — until you need your age in months for a form, in days for a milestone, or you were born on February 29. Here’s how age calculation actually works, and the quickest ways to get an exact answer.
The basic method
Your age in years is the number of complete years since your birth date:
- Take the current year minus your birth year.
- Subtract 1 if your birthday hasn’t happened yet this year.
Someone born on October 10, 2000 is 25 years old in July 2026 — because their 26th birthday (October 2026) hasn’t arrived. Skip the second step and you get the wrong answer for roughly half the year.
For an instant result — including months, weeks, days and a countdown to your next birthday — use the free Age Calculator. Or if you just know your birth year, our born-in pages show the age range for every year at a glance.
Age in months and days
Forms for babies, medical records and legal documents often need finer detail. The convention:
- Months: count complete calendar months from your birth date. From Jan 15 to Apr 14 is 2 months; Jan 15 to Apr 15 is exactly 3.
- Days: count the remaining days after complete months. Someone born March 10, 2024 is — on July 25, 2026 — exactly 2 years, 4 months and 15 days old.
Because months have different lengths, two people born 30 days apart can have different “months + days” ages. Calculators handle this by walking through calendar months rather than dividing by 30.4.
The leap year question
Born on February 29? You have a birthday every four years, but legally you age every year like everyone else. Most jurisdictions treat March 1 (or February 28, depending on the country) as the legal birthday in non-leap years. Your age in days is unaffected — leap years just shift the calendar labels.
Leap years also matter for day counts: a year is 365 days, except every fourth year (366), except century years not divisible by 400. It’s why “age in days” from mental math is nearly always off by a few days.
Some fun age math
- 10,000 days old happens at age 27 years, 4½ months — a milestone most people miss.
- Your 1,000th week arrives just past your 19th birthday.
- A billion seconds is about 31.7 years.
Count the days to any of these with the Days Until Calculator.
Frequently asked questions
How is age calculated in East Asia? Traditional Korean age counted people as 1 at birth and added a year every New Year — but South Korea officially switched to international age in 2023.
What’s my age for insurance or visas? Nearly all legal contexts worldwide use completed years (international age) as described above.
How do I calculate age in Excel? =DATEDIF(birthdate, TODAY(), "Y") gives complete years; swap "Y" for "YM" or "MD" for the month and day parts.
Get your exact age — years, months, weeks, days, hours and time to your next birthday — with the free Age Calculator.