Date/Time
Age Calculator
Calculate your exact age in years, months, and days from your date of birth. Also shows total days lived, weeks, days until next birthday, day of the week you were born, and Japanese era.
- Days alive
- [[ result.totalDays.toLocaleString('ja-JP') ]] days / [[ result.totalWeeks.toLocaleString('ja-JP') ]] weeks
- Next birthday
- 🎉 Today! [[ nextBirthdayFormatted ]]（[[ result.nextBirthdayDays ]] days away）
- Born on
- [[ birthDayOfWeekName ]]
- Japanese era
- [[ wareki ]]
Tips for Age Calculation
- Age is calculated based on calendar years, months, and days. The day count accounts for leap years, so it may differ slightly from 365 × years.
- If your next birthday is today, the countdown shows 0 days.
- For birthdays on February 29th, this calculator uses February 28th in non-leap years — the most common legal interpretation in Japan.
- The "days alive" count is computed precisely, including all leap days since your birth.
FAQ
Side Note — Ways of Counting Age Around the World
Japan currently uses the "full age" (満年齢) system where age increases on the birthday — the same system used in most Western countries. Until the Meiji era, Japan used "kazoe-doshi" (数え年), where a newborn is considered 1 year old at birth and gains a year on every New Year's Day.
South Korea traditionally used a similar system (세는 나이) where everyone is born at age 1 and turns a year older on January 1st, making Korean ages 1–2 years higher than Western ages. In June 2023, Korea officially standardized legal age to the international system, though the traditional counting persists in daily speech.
Japan's milestone birthdays have poetic names: Kanreki (還暦, 60) marks one full cycle of the zodiac; Koki (古希, 70) comes from a Du Fu poem meaning "rare to reach 70"; Kiju (喜寿, 77) gets its name because the cursive kanji for 喜 looks like 七十七.