3 min read · Time
Working out someone’s age in whole years is easy. Getting the exact years, months, and days, or an age in total days, takes a little more care because months have different lengths.
Step by step
Start with whole years: subtract the birth year from the current year, then subtract one more if this year’s birthday hasn’t happened yet.
Next, count whole months from the most recent birthday to today, and finally the remaining days. For example, someone born on March 15, 1990 is 36 years, 6 months, and 13 days old on September 28, 2026.
For an age in days, count the days between the two dates directly. It is easy to miss leap days by hand, which is where a calculator helps.
Leap-day birthdays
People born on February 29 only have a calendar birthday every four years. In other years, the legal birthday is usually treated as either February 28 or March 1, depending on the country and the purpose, for example for driving licenses or reaching legal age.
Different ways of counting age
Most of the world counts age from zero at birth and adds a year on each birthday. Some East Asian traditions count a baby as one year old at birth and add a year every Lunar New Year or January 1. South Korea officially switched to the international method for legal and administrative purposes in June 2023, though traditional counting is still used socially.
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