🧮 Calculators & Daily Life

Kyūreki (Japanese Lunar Date) Converter

Convert a Gregorian date to the Japanese lunar calendar (Tenpō rules) and back, including leap months and the 2033 ambiguity (solstice-priority method).

Examples (click to try)

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Related articles

The Kyureki 2033 Problem — When the Lunar Calendar's Months Become Undefined Under the Tenpo rules, the lunar month names for late 2033–2034 aren't uniquely defined. We show the solstice-priority method Benri.dev uses and how methods diverge.

How to use

Enter a Gregorian date to see the lunar month and day (with a leap mark and the month length). The reverse direction takes a lunar month/day and the civil year it belongs to.

Examples

  • 17 Feb 2026 → lunar 1/1 (New Year), plus that month's length
  • 7 Feb 2027 → lunar 1/1 (Japanese New Year; the new moon is 00:56 JST on 7 Feb. Chinese Spring Festival is 6 Feb in CST)
  • 6 Feb 2027 → lunar 12/30
  • 1 Jan 2026 → lunar 11/13. The reverse lookup for “2026, lunar 11/13” defaults to the later date, 21 Dec (the earlier is 1 Jan)
  • 22 Dec 2033 → leap 11/1 (solstice-priority)

Related tools

Era years: wareki converter. Rokuyo: rokuyo calendar. Solar terms: 24 solar terms. The 2033 problem is explained in an article.

FAQ

Is the date sent to a server?
No. Conversion runs entirely in your browser; nothing is transmitted or stored externally.
How are leap months and a 30th day in a short month handled?
A leap month keeps the same month number and is marked leap. If a short month has no 30th day, the tool says so and shows that month's length.
How do you handle the 2033 kyūreki ambiguity?
We use the solstice-priority method this site adopted. 22 December 2033 is leap month 11, day 1. Printed calendars may disagree in that window.
Can I see today's lunar date immediately?
On load, today's date (from your device) is placed in the Gregorian field and converted. Example chips cover New Year's Day and leap month 11.
How does this relate to rokuyo and lucky days?
Rokuyo is computed from the lunar month and day. You can cross-check the result on the rokuyo and lucky-day calendars.
Isn’t the 2027 lunar New Year on 6 February?
The Japanese lunar New Year is the civil day of the new moon. In 2027 that instant is 00:56 JST on 7 February, so 7 February is lunar 1/1 and 6 February is lunar 12/30. Chinese Spring Festival is 6 February in CST.
Why can Gregorian → lunar → Gregorian change the date?
Lunar months 11 and 12 can occur twice in the same civil year. The reverse conversion defaults to the later date. Switching from Gregorian keeps the original day and also shows the other occurrence.