Find your exact age and days until your next birthday
Age Is More Complicated Than You Think Calculate your exact age in years, months, and days from your date of birth. The calculation is straightforward in most cases, but the concept of age turns out to be more complex and culturally variable than most people realize. Legal age calculations handle edge cases that date arithmetic alone cannot resolve. The most common: what is the legal birthday of someone born on February 29 in a leap year? In most jurisdictions, courts have ruled that leap-year birthdays fall on February 28 in non-leap years — making someone born on February 29, 2000 legally 18 on February 28, 2018 in the United States. Some jurisdictions use March 1 instead. This distinction occasionally matters for driver's licenses, alcohol purchase age limits, and voting eligibility — one day in either direction can determine whether a specific act is legal or not. Beyond chronological age — the time elapsed since your birth — there is the concept of biological age, which measures how old your body is functioning relative to chronological norms. Epigenetic clocks, developed from research into DNA methylation patterns, can estimate biological age from a blood sample with increasing accuracy. People with the same chronological age can have biological ages that differ by a decade or more, reflecting differences in lifestyle, genetics, and environment. Biological age has practical implications: some insurance underwriters and pharmaceutical researchers now use epigenetic markers as a more accurate predictor of health risk than birth year alone. Cultural age reckoning varies significantly around the world. The most widely known alternative system is the East Asian age reckoning tradition, historically used in Korea, Japan, China, and Vietnam. Under this system, a person is considered one year old at birth (accounting for time spent in the womb) and gains an additional year on New Year's Day rather than their birthday. This means someone born on December 31 under the traditional system would be considered two years old by January 2. South Korea officially abolished traditional age reckoning for legal purposes in 2023, shifting fully to the international system. Japan had made the transition decades earlier. Chronological age calculated from a birth date remains the legal standard almost everywhere for purposes ranging from retirement eligibility to medical drug dosing charts.
Most US jurisdictions treat February 28 as the legal birthday for people born on February 29 in non-leap years. Some use March 1. This matters for age-restricted activities like voting and driver's licenses, where a single day determines eligibility.
Chronological age is simply time elapsed since birth. Biological age, measured through epigenetic markers like DNA methylation patterns, reflects how old your body is actually functioning. People of the same chronological age can have biological ages differing by a decade based on genetics and lifestyle.
In the traditional East Asian system, a person is considered age 1 at birth and gains a year on New Year's Day, not their birthday. Someone born in December could be considered two years old by January 2. South Korea officially switched to the international system in 2023.