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週番号計算機

Week number calculator: get ISO week number and start end dates from date for scheduling and projects, with one-click copy, offline.

使い方

日付を入力すると ISO 週番号と年内日数がリアルタイムに計算されます。

Overview

Week Number Calculator is a Time tool. Get ISO week number and start end dates from date for scheduling and projects, with one-click copy, offline. It runs 100% in your browser with no upload, so you get instant results with privacy. Whether you need a quick answer or batch processing with precise control, you can enter, validate and export in seconds. The UI is responsive on mobile, tablet and desktop and supports one-click copy.

Use cases

  • Daily use of Week Number Calculator: Enter a date to get its ISO week and day of year. — enter and get instant results without manual lookup.
  • One-click copy keeps results ready to save, check or share with family and pros.
  • Use Week Number Calculator offline or on poor network — all calculations stay local and private.
  • Exact age and total days
  • Birthday and lunar reminders

How to use

  1. 1 Enter a date to get its ISO week and day of year..
  2. 2 Toggle inclusive and workdays
  3. 3 View weeks/months/hours breakdown
  4. 4 Copy or add to calendar

Highlights

  • Local & private: processing stays in your browser
  • Live validation with tolerant parsing
  • One-click copy and export for docs, code or sheets
  • Batch and offline support under poor network

Notes

  • Feb 29 birthdays vary by locale
  • Seconds vs milliseconds timestamps
  • Workdays need holiday data

FAQ

Lunar supported?
Yes, lunar input auto-converts to Gregorian.
Why different ages?
Years-old vs nominal age differ by region.
How is Week Number Calculator different?
It runs locally with a focus on speed and privacy, plus tolerant parsing for “week number” and one-click copy for reuse.
Can I use results in official reports?
Use it as a working draft and cross-check with authoritative sources; keep the exported log and parameters for traceability.
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すべての計算はブラウザ内で実行され、データはアップロードされません。