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日付間隔計算機

2つの日付の間の日数を数え、週数と年・月・日での期間を表示します。

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このツールの詳しい解説（使い方、例、よくある質問）は、現在英語のみでご用意しています。

What this tool does

Pick a start date and an end date. You get the number of days, how that breaks into weeks and leftover days, and a calendar span in years, months, and days.

How to use

  1. Choose the start date and the end date.
  2. Press Calculate.
  3. Read the total days first when you need an exact count.
  4. Use the years, months, and days line when you want a calendar description.

Examples

  • 1 March to 1 April in a non-leap year

    The exact count is 31 days, which is 4 weeks and 3 days. The calendar span is 0 years, 1 month, and 0 days. Those two descriptions are both right. They are not the same unit.

  • The same date twice

    Start and end on 2026-09-23. Total days is 0. Weeks and extra days are 0. The calendar span is 0 years, 0 months, and 0 days.

Main features

  • Exact day count, including a same-day result of 0.
  • Weeks plus the leftover days.
  • A calendar span that borrows days and months the way a calendar does.
  • A separate average-month figure, labeled as an average.

How it works

Total days counts midnights between the two dates. Weeks are that count divided by 7. The year, month, and day line walks the calendar: if the end day is earlier in the month, it borrows the length of the previous month. That length changes. February is not 30 days. The average-month number divides the day count by 30.44 and is only a rough size. It is not a second calendar result.

Tips

  • Use total days for a deadline. Use the calendar span when you are describing a rental, a subscription, or an age-like period.
  • If the end date is earlier, the page still shows a positive span and says the dates were reversed.

Limitations

Calendar months do not have one fixed length, so “1 month” is not always 30 days. The average-month line is not an exact month count. Time of day is ignored.

See the disclaimer for what these tools do not cover.

FAQ

What if the end date is before the start date?
The counts stay positive and a note says the end date is earlier. The span runs from the later date back to the earlier one.
Does February change the result?
Yes, for the calendar span. A period that crosses February uses that month’s real length. The total day count is still exact.
Is my input sent to a server?
No. The two dates are counted in this tab. They are not uploaded.
How do I count the days between two dates?
Choose the start and end dates and calculate. The total days are the exact count, and weeks and years, months, and days describe the same span.
Is the end date included in the count?
The count is the number of days from the start date to the end date, so the start day itself is not added. Add 1 if you need to include both days.

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