うるう年計算機

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はじめに

Leap Year Calculator — Check if a year is a leap year and how many days it has. Enter Year to get an instant, accurate result.

計算式

A year is a leap year if it's divisible by 4, except century years, which must also be divisible by 400 (so 2000 is a leap year but 1900 is not).

ステップごとの説明

1. Enter the Year.
2. Click Calculate to see your result instantly.

実例

Example: With Year = 2026, the Leap Year Calculator gives Is Leap Year: no, Days In Year: 365.

よくある質問

Why isn't every 4th year a leap year?

Century years divisible by 4 but not by 400 (like 1900 or 2100) are skipped to keep the calendar closely aligned with Earth's actual orbit.

How many days are in a leap year?

366 days, with the extra day added as February 29.

What inputs does the Leap Year Calculator need?

You'll need to provide: Year. All fields use sensible defaults, so you can see a working example immediately and then adjust the values to match your own numbers.

How accurate is the Leap Year Calculator?

The Leap Year Calculator applies the formula exactly as calculated — A year is a leap year if it's divisible by 4, except century years, which must also be divisible by 400 (so 2000 is a leap year but 1900 is not). — so results are precise for the inputs you provide. Accuracy depends on entering correct, realistic input values.

Is the Leap Year Calculator free to use?

Yes, the Leap Year Calculator is completely free, requires no signup, and runs instantly in your browser.

うるう年計算機について

The Leap Year Calculator uses a real, verifiable formula — A year is a leap year if it's divisible by 4, except century years, which must also be divisible by 400 (so 2000 is a leap year but 1900 is not). — so results are accurate every time, not an approximation.