How exact age is calculated
Your age in years is the number of birthdays you have had. To get the full answer in years, months and days, this calculator counts whole calendar months from your date of birth until the most recent “monthiversary” on or before the target date, then counts the remaining days. Someone born on May 15, 1990 is exactly 36 years, 5 months and 0 days old on October 15, 2026. On October 20 they would be 36 years, 5 months and 5 days.
Counting by calendar months handles months of different lengths correctly. Someone born on January 31 reaches one month old on the last day of February, since February has no 31st, and the leftover days are counted from there.
Age in months, weeks and days
The calculator also shows your age as a single number of months, weeks and days. Total days are counted exactly between the two dates, including leap days, so a 30-year-old has lived roughly 10,957 days. Weeks are the total days divided by seven, rounded down. These figures are handy for baby milestones, which are usually tracked in weeks for the first few months and in months until age two, and for fun facts like celebrating your 10,000th day, which falls a few months before your 28th birthday.
Leap year birthdays
People born on February 29 have a birthday on the calendar only once every four years. Legally, most jurisdictions treat them as turning a year older on March 1 in common years, although many people celebrate on February 28. This calculator treats the birthday as February 28 in non-leap years when counting the next birthday, and counts age in whole months in the same way. If a specific legal date matters, for example for a driver’s license, retirement benefits or age-restricted purchases, check the rule where you live.
Different ways of counting age
The international standard, used here, starts at zero at birth and adds a year on each birthday. Traditionally in Korea, China and some other East Asian cultures, babies were considered one year old at birth and everyone gained a year at the Lunar New Year, so a person’s traditional age could be one or two years more than their international age. South Korea officially adopted the international method for legal and administrative purposes in 2023.
You can also change the “age as of” date to find out how old someone was, or will be, on any date: useful for historical research, eligibility deadlines, school entry cut-offs or planning a milestone birthday party. The day of the week you were born is shown as a bonus.
Frequently asked questions
How do I calculate my exact age?
Count the full years since your birth date, then the full months since your last birthday, then the remaining days. The calculator does this automatically.
How many days old am I?
Enter your date of birth and the calculator shows your exact age in days, counting leap years.
When do leap-day babies have birthdays?
In non-leap years many celebrate on February 28 or March 1. Legally, March 1 is common, but rules vary by place.
Can I calculate age on a future date?
Yes. Change the “age as of” date to any past or future date.