ISO Week Number Calculator

Calculate the official ISO-8601 week number (Week 1 to Week 53), week-numbering year, day of week, and start/end dates for any selected date.

Why Use This Converter?

• Business & Project Planning: Align project milestones and sprint schedules with international ISO calendar week numbers (e.g., `2026-W34`).
• Supply Chain & Logistics: Coordinate manufacturing and shipping delivery schedules using ISO week numbers.
• Financial Reporting: Group weekly sales and operational data according to ISO calendar standards.

How to Use

1. Select any calendar date or enter a date string.
2. The tool calculates the exact ISO week number (e.g. Week 34).
3. View week start (Monday) and week end (Sunday) date ranges.

Real Conversion Example

Input (TEXT):

2026-08-18

Output (TEXT):

ISO Week Number: Week 34 (2026-W34)
Day of Week: Tuesday (Day 2)
Week Date Range: Mon, Aug 17, 2026 – Sun, Aug 23, 2026

Important Technical Details & Mechanics

• ISO-8601 Rule Engine: Follows the official ISO 8601 rule: Week 1 is the week containing the first Thursday of the calendar year.
• Monday-Start Calendar: Considers Monday as Day 1 of the week according to international standards.
• Client-Side Engine: Instant calculation in browser memory.

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