Chronological Age Calculator

Subtract the birth date from the date you're measuring as of, working in whole calendar units: count the completed years first, then the leftover completed months, then the leftover days — the same method a court, school, or medical form uses, not a fixed 30-day-per-month estimate. Enter both dates above and the calculator runs that exact calendar subtraction for you, including every leap day that falls inside the span, and also returns the total number of days lived as a single unambiguous figure alongside the years-months-days breakdown.

Chronological age is simply the calendar time since birth — exactly what this calculator returns, and what appears on a birth certificate, driver's license, or medical chart. Biological age is a different, non-calendar measure: an estimate of how old a person's body appears to be functioning based on factors like genetics, fitness, diet, sleep, and chronic disease markers, sometimes generated from blood panels or specialized health assessments. Two people with an identical chronological age can have meaningfully different biological ages. This calculator only computes chronological age; estimating biological age requires clinical data this tool doesn't collect.

Most of the world, and this calculator, uses the international system: age zero at birth, with a year added on each birthday. Traditional East Asian age reckoning, historically used in Korea, China, and Vietnam, instead starts a baby at age one and adds a year to everyone on New Year's Day rather than on individual birthdays, which can put someone one or two years ahead of their international age depending on when their birthday falls.

Korean age counts a baby as one year old at birth, then adds a year to everyone on New Year's Day rather than on individual birthdays, so it can run one or two years ahead of international age depending on the birth date. South Korea made international age the sole legal standard for contracts and government records on June 28, 2023, though Korean age is still used casually in everyday conversation.

Traditional East Asian age reckoning starts a newborn at age one instead of zero, a convention with roots in treating the time spent in the womb as already part of a person's life rather than something that precedes it. Combined with adding a year to everyone on New Year's Day instead of on individual birthdays, the result is an age that can sit one or two years above the internationally counted figure for the same person.

Multiply the "Years" figure above by 12, then add the "Months" figure, for a single total-months count. Someone shown as 26 years and 1 month above is 313 months old (26 × 12, plus 1). Age in months comes up most often for young children, where a milestone or a corrected age for a premature baby is easier to track in months than in years.

That's the "Total days lived" figure this calculator returns alongside years, months, and days — a straightforward day count between the birth date and the "as of" date, leap days included. Unlike years-months-days, which depends on how you define borrowing across month boundaries, a total day count is unambiguous, which is why it's the figure used for things like medical dosing schedules that scale with age.

Eighteen in most U.S. states, but Alabama and Nebraska set it at 19 and Mississippi at 21. Age of majority is also distinct from specific rights: the U.S. minimum drinking age is 21 nationwide regardless of a state's general age of majority, and other rights, like driving or gambling, follow their own separate age rules. This is general background, not legal advice, for anything a specific decision depends on.

No. Eighteen is the most common age of majority worldwide, but Scotland, Vietnam, Cuba, and Cambodia set it at 16; Thailand and New Zealand at 20; and several countries, including Egypt, Kuwait, and the United Arab Emirates, at 21. Japan lowered its age of majority from 20 to 18 in 2022. Rights like voting, drinking, and driving are frequently set at different ages than the general age of majority, even within the same country.

Corrected (or adjusted) age is a premature baby's chronological age minus however many weeks or months early they were born — effectively the age they'd be if born on their original due date. A baby born three months early who is chronologically one year old has a corrected age of about nine months. Healthcare providers generally track development against corrected age rather than chronological age until around two years old.

Districts calculate age as of a fixed cutoff date, often between late July and early September, rather than as of today. A child who reaches the minimum enrollment age, commonly five, before that cutoff date qualifies to start that year; a child who turns five even one day after the cutoff typically waits a full additional year. It's the same age-as-of-a-date calculation this tool runs, just with an enrollment cutoff entered instead of today.

Set the "as of" date to August 31 of the current year and enter the child's birth date — that's Little League Baseball's official age determination date, used since the 2018 season so divisions line up with the school year. Little League Softball uses December 31 of the previous year instead. A player's league age then stays fixed for the whole season, even if a birthday falls afterward.

It's a popular rule of thumb, not a legal standard, for the youngest age someone should date: take your age, halve it, then add seven. A 30-year-old, by this formula, shouldn't date anyone younger than 22. Enter both birth dates into this calculator to get each person's exact age, then apply the formula yourself — the calculator handles the age math, not the rule itself.

International age, always — the system in which a person is zero years old at birth and gains a year on each individual birthday. That's the standard used for legal documents, medical records, and everyday conversation nearly everywhere today, including in South Korea since June 2023. If you have an age quoted in Korean age or another traditional East Asian system, treat it as a different figure rather than assuming it matches this calculator's result.