日付の加算・減算
基準日に年・月・週・日・営業日を加算または減算します。
操作
結果
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月末の扱い
開始日の日にちが対象の月に存在しない場合、その月の最終日に調整されます。例：1月31日 + 1か月 = 2月28日（うるう年は2月29日）。
例
- 2026-01-31 + 1 month = 2026-02-28 (month-end rule applied).
- 2024-01-31 + 1 month = 2024-02-29 (leap year).
- 2026-07-24 (Friday) + 3 business days = 2026-07-29 (Wednesday) — the weekend is skipped.
よくある質問
What happens with January 31 + 1 month?
February has no 31st, so the result is clamped to the last day of February — the 28th, or the 29th in a leap year. The tool tells you whenever this month-end rule was applied.
How do business days differ from calendar days here?
In business-day mode the tool steps one weekday at a time, skipping Saturdays, Sundays, and (if you pick a country) its public holidays. Adding 5 business days to a Friday therefore lands on the following Friday, not on Wednesday.
Are years and months added before or after days?
Years and months are applied first (with month-end clamping), then weeks and days. This matches how contracts and deadlines are usually interpreted, and it makes the calculation explainable step by step.