日付の差を計算
2つの日付の間隔を計算します。
日付と時刻
週番号計算
ISO週番号と年初からの日数を調べます。
入力内容
UtilBrix が提供結果
ISO week number
43
- ISO week year
- 2,026
- Week start (Monday)
- 2026-10-19
- Week end (Sunday)
- 2026-10-25
- Day of year
- 292
- ISO weeks remaining
- 10
詳しい方法と使用例は英語で提供しています。
Step-by-step instructions (English)
- Select the calendar date you want to inspect.
- Calculate its ISO week number and ISO week year.
- Read the Monday-to-Sunday week range and day-of-year value alongside the number.
計算式と方法
ISO 8601 weeks start on Monday. Week 1 is the week containing 4 January, so dates near New Year can belong to the previous or next ISO week year. Weeks remaining refers to that ISO year.
使用例
1 January 2021 falls in ISO week 53 of 2020. The week runs from 28 December 2020 through 3 January 2021.
When this tool is useful
Label a weekly report, identify a sprint week, or match a date to an ISO-based planning calendar. Include the ISO year when sharing a week number around New Year to prevent ambiguity.
Common mistakes and limitations
- The ISO week year can differ from the ordinary calendar year near January 1.
- Some calendar applications use Sunday-start or other numbering systems; compare the convention before comparing results.
Practical questions about this tool (English)
Why is January 1 sometimes in week 52 or 53?
ISO week 1 is the week containing January 4. Early January dates can therefore belong to the final ISO week of the previous year.
What is the first day of an ISO week?
Monday. This tool does not switch the week-number convention when you change display language.