ISO週番号計算

ISO週番号を計算

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Select Date

ISO Week

W14

2026-W14-3

ISO Year

2026

ISO Weekday

3 (Wednesday)

Week 14 Range

Start (Monday):Mar 30, 2026End (Sunday):Apr 5, 2026

Days in This ISO Week

Mon

Tue

Wed

Thu

Fri

Sat

Sun

Find Date from ISO Week

Year

Week

Day (1-7)

Monday, December 29, 2025

2026 ISO Weeks Overview

Total weeks:53First week starts:Dec 29, 2025Last week ends:Jan 3, 2027Week type:Long year

ISO Week Rules

ISO 8601 week date standard:

Weeks start on Monday (day 1) and end on Sunday (day 7)
Week 1 is the week containing the first Thursday of the year
Equivalently: Week 1 contains January 4th
A year can have 52 or 53 weeks
Dec 31 might be in week 1 of next year
Jan 1 might be in week 52/53 of previous year

ISO Week format: YYYY-Www-D

Example: 2024-W15-3 = Wednesday of week 15, 2024

About ISO週番号計算

ISO週番号を計算

Use this free online 日付・時刻ツール tool to work faster without installing extra software. The interface is built for quick input, clear output, and straightforward results on desktop and mobile devices.

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This tool runs in your browser whenever possible, which keeps your inputs private and reduces unnecessary round-trips to the server.

ISO週番号計算

About ISO週番号計算

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