How Japan's Public Holidays Are Decided — Substitute Holidays and the Equinox

"When is Marine Day this year again?" If you try to memorize Japan's holidays as a fixed list, they keep shifting on you. That is because Japan's national holidays are set by the Act on National Holidays (the "Holiday Law"), not by a table. Alongside date-fixed holidays there are holidays that move by weekday and rules that fill gaps between holidays — and once you know them, you can work out this year's long weekends yourself. Our Japanese public holidays tool computes every year with exactly these rules.

1. "Happy Monday" holidays that move by weekday

Since 2000, several holidays were moved to "the Nth Monday of a month," so their dates change every year (the Happy Monday system). The goal is to line them up with the weekend for a three-day break. Four holidays are affected:

So memorizing "Marine Day is July 20" will fail. You have to recompute the Nth-Monday each year.

2. The "substitute holiday" when a holiday lands on Sunday

When a holiday falls on a Sunday, the first following day that is not a holiday becomes a day off. This is a substitute holiday. Usually that is the next Monday, but if the next day is also a holiday, it slides further to the next non-holiday weekday. It is not simply "Sunday holiday means Monday off."

3. The "citizens' holiday" sandwiched between two holidays

A weekday with a holiday on both the day before and the day after becomes a day off. This is a citizens' holiday. Today it mainly appears in September, in years where Respect-for-the-Aged Day (3rd Monday) and the Autumnal Equinox fall one day apart, with a single weekday between them.

In 2026, for example, Respect-for-the-Aged Day is Mon Sep 21 → a citizens' holiday on Tue Sep 22 → the Autumnal Equinox on Wed Sep 23. With the preceding Saturday (Sep 19) and Sunday (Sep 20), that makes a five-day break, Sep 19–23 (Japan's "Silver Week"). By our calculation, September citizens' holidays occur on these 14 occasions between 2003 and 2099:

Why the equinox holidays are only fixed the year before

The Vernal and Autumnal Equinox holidays have no fixed date. They fall on the day containing the moment the sun's ecliptic longitude reaches 0° (spring) or 180° (autumn) — an astronomical event, so the date drifts from year to year. They can be computed far ahead in principle, but the legally official date is only fixed once it is published in the official gazette in February of the previous year. That is why a holiday calendar must distinguish "provisional" from "confirmed." We compute the autumnal equinox as ecliptic longitude 180°.

FAQ

The citizens'-holiday years and equinox dates here were computed by us (ecliptic longitude 180° plus the Holiday Law rules; as of 2026-07-16). Future years use provisional dates under current law and may change if the law is amended.