siutil. wareki
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Gregorian → Japanese era

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Japanese era → Gregorian

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A date calculator for the three things that trip people up on Japanese paperwork: "which Reiwa year is this?", "how old is that?", and "how many business days away is that?". Switch tabs for three calculators. (1) Era ⇄ year: enter a Western date and it tells you the matching Japanese era — Reiwa, Heisei, Shōwa, Taishō or Meiji — and the reverse, turning an era and year back into a Western year. Era boundaries are handled to the exact day, so 7 Jan 1989 is Shōwa 64 while 8 Jan 1989 is Heisei 1, and 30 Apr 2019 is Heisei 31 while 1 May 2019 is Reiwa 1. The year's Chinese zodiac sign is shown too. (2) Age: from a date of birth and a reference date (today by default) it gives the full age in years, the exact "years / months / days" breakdown, the total number of days lived, and the birth date written in the Japanese era with its zodiac sign. (3) Days & business days: enter two dates and it counts calendar days (difference and inclusive), weekdays (Mon–Fri), weekend days, and business days excluding Japanese national holidays. Holidays are computed from the law — fixed-date holidays, the "Happy Monday" holidays (Coming-of-Age Day, Marine Day, Respect-for-the-Aged Day, Sports Day), the spring and autumn equinoxes, plus substitute holidays and "citizens' holidays" — including the 2020/2021 Olympic moves. Use it for document expiry dates, deadlines, payment dates, or just to confirm someone's age. The dates and birthdays you enter are personal data, so this tool uploads nothing: conversion, age, and day counting all happen locally in your browser.

How to use

  1. Pick a calculator with the tabs at the top: Era ⇄ Year, Age, or Days / business days.
  2. For Era ⇄ Year, enter a date or choose an era and year; for Age, enter a date of birth and reference date; for days, enter a start and end date.
  3. The result (Reiwa year / age / business days) updates instantly. Nothing you enter is sent anywhere.

FAQ

Are the dates or birthdays I enter uploaded?

No. Era conversion, age, and day counting all run in your browser. The dates and birthdays you enter are never uploaded, stored, or sent anywhere — everything is processed only on your device.

Does it handle the year an era changes (Shōwa→Heisei, Heisei→Reiwa)?

Yes. Era boundaries are handled to the exact day. 7 Jan 1989 is Shōwa 64 and 8 Jan 1989 is Heisei 1; 30 Apr 2019 is Heisei 31 and 1 May 2019 is Reiwa 1. The same Western year can map to different eras depending on the date.

Does the business-day count exclude Japanese public holidays?

Yes. It counts Monday–Friday and then removes Japanese national holidays. Alongside fixed-date holidays it computes the "Happy Monday" holidays (Coming-of-Age, Marine, Respect-for-the-Aged, Sports Day), the spring and autumn equinoxes, and substitute / citizens' holidays — including the 2020 and 2021 Olympic moves. Holidays are derived from the law rather than a stored table, so it's reliable roughly from 2000 to 2099.

How is the age calculated?

It uses the common full-age (man'nenrei) method, where a year is added on the birthday itself. It computes the age as of the reference date (today by default) and also shows the exact years / months / days breakdown and the total days lived. The Japanese school-year edge case (aging on the day before the birthday) is not applied.

Can it convert dates before the Meiji era?

It supports Meiji through Reiwa. Note that before 1873 (Meiji 6) Japan used a lunisolar calendar, so the correspondence with the Western calendar before then is approximate. For convenience this tool treats 1868 as Meiji 1.

Can it convert both ways — Western to Japanese and back?

Yes. The Era ⇄ Year tab converts both directions. Enter a Western date to see the era, year and zodiac; or choose an era and year to get the matching Western year. If you enter a year that doesn't exist in that era (for example Heisei 32) it tells you it's out of range.