曜日計算ツール

Find what day of the week any date falls on, next/previous occurrence of a weekday, and count or list weekdays in a range with step-by-step solutions.

Your Input

Format: YYYY-MM-DD

Select a calculation type, enter your dates and weekday, then click Calculate to see results with step-by-step solutions.

完全なユーザーガイド

曜日計算ツールとは何ですか?

A day of week calculator finds which weekday (Monday–Sunday) any date falls on, the next or previous occurrence of a chosen weekday, and how many times (or which dates) a weekday appears in a date range. It uses the Gregorian calendar and handles leap years and varying month lengths.

Weekday index: 0=Monday … 6=Sunday  |  Weekdays Mon–Fri; weekends Sat–Sun

Use it for scheduling, planning recurring events, or checking if a date is a weekday or weekend.

Date Format

Use YYYY-MM-DD (e.g. 2025-02-15). Dates from year 1 to 9999 are supported.

計算の種類

曜日の検索

Enter any date to see which weekday it is and whether it's a weekday or weekend.

次の出現

From a date, find the next occurrence of a chosen weekday (e.g. next Monday).

前回の発生

From a date, find the previous occurrence of a chosen weekday.

平日を数える

Count how many times a specific weekday appears in a date range; includes chart.

すべての出現箇所を検索

List all dates in a range that fall on a chosen weekday (e.g. all Mondays; up to 20 shown).

この計算機の使い方

  1. Select a calculation type (Find Day, Next/Previous Occurrence, Count Weekdays, or Find All Occurrences)
  2. Enter the required dates and choose a weekday where needed
  3. Click 'Calculate' to see the result
  4. Review the main result, detail card (weekday/weekend), occurrences list, and step-by-step solution
  5. Use the chart when counting weekdays for a visual breakdown
  6. Click 'Reset' to set all dates to today and clear results

結果を理解する

Main result

The weekday name, result date, or count—depending on the mode. The subtitle shows the date or a short description.

Detail card

For Find Day of Week: indicates whether the date is a Weekday (Mon–Fri) or Weekend (Sat–Sun).

Occurrences list

For Find All Occurrences: lists the dates in the range that fall on the chosen weekday (up to 20).

平日を理解する

The calculator uses weekday index 0=Monday through 6=Sunday. Weekdays are Monday–Friday; weekends are Saturday and Sunday.

  • 0 = 月曜日
  • 1 = 火曜日
  • 2 = 水曜日
  • 3 = 木曜日
  • 4 = 金曜日
  • 5 = 土曜日
  • 6 = 日曜日

重要な注意事項

  • Uses Gregorian calendar; leap years and varying month lengths are handled.
  • Weekday index: 0=Monday … 6=Sunday. Weekdays Mon–Fri; weekends Sat–Sun.
  • Dates must be between year 1 and 9999. Use YYYY-MM-DD format.

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