Converting Between Wareki and Gregorian Years
How wareki-to-Gregorian conversion works, why 1989 and 2019 each contain two era names, and why Meiji (1868-10-23) is the usual starting point.
What is the Japanese era system (wareki)?
Wareki counts years from the start of an emperor's reign rather than from a fixed epoch. It's used alongside the Gregorian calendar in Japanese administrative documents and everyday life. The main difference from the Gregorian calendar is that the year count resets to 1 every time a new era — Reiwa, Heisei, Showa, Taisho, Meiji — begins.
The formula for converting between wareki and Gregorian years
The core formula is: wareki year = Gregorian year - era start year + 1, and Gregorian year = era start year + wareki year - 1. Reiwa began in 2019, so 2026 becomes 2026 - 2019 + 1 = 8, or Reiwa 8. The month and day carry over unchanged across a conversion — only the year numbering changes.
Transition years: some years contain two era names
When an era change happens partway through a year, that single Gregorian year holds two era names. In 1989, January 1 through January 7 is Showa 64, and January 8 onward is Heisei 1 (also written Heisei gannen). In 2019, January 1 through April 30 is Heisei 31, and May 1 onward is Reiwa 1 (Reiwa gannen). Converting by year alone, without checking the exact date, misassigns the era for these two years.
When does the Meiji era begin?
Meiji began on October 23, 1868. Japan also used a lunisolar calendar through Meiji 5 (1872), switching to the solar Gregorian calendar starting Meiji 6, January 1. Because of that calendar switch, most wareki conversion tools cover Meiji 6 (1873) onward; dates before that used a different calendar system entirely, so a simple year-shift conversion doesn't apply.
Do the month and day stay the same across eras?
From Meiji 6 onward, yes — only the year number changes between wareki and the Gregorian calendar; the month and day are identical. Even in a transition year, you keep the same month and day and simply recount the year against whichever era's start date applies.
A notation quirk worth knowing
The first year of an era is conventionally written as gannen (元年) rather than '1' — for example, Reiwa gannen instead of Reiwa 1. Documents mix both forms, so any system handling wareki dates should treat 'era name + gannen' and 'era name + 1' as the same year.
Frequently asked questions
What Gregorian year did Reiwa start in?
May 1, 2019. January 1 through April 30 of that year is still Heisei 31.
What Showa year does 1989 correspond to?
January 1 through January 7 is Showa 64; January 8 onward is Heisei 1 (Heisei gannen).
Can dates before Meiji be converted?
Standard tools cover Meiji 6 (1873) onward, when Japan adopted the solar calendar. Earlier dates used a lunisolar calendar, so a simple year conversion doesn't apply.