Week Number Calculator

📆 Week Number Calculator — Find the Week of the Year

Welcome to the Free Week Number Calculator on calculator.cl — your simple tool for finding the week number of a given date. Whether you’re planning projects, tracking schedules, or organizing events, knowing the week of the year can be incredibly useful.

This calculator works with the ISO standard for week numbering and gives you an instant result — no login or signup required.

🧠 What Is a Week Number?

A week number shows which week of the year a particular date falls in. The most commonly used system is the ISO week date system, where:

Weeks start on Monday

The first week of the year contains January 4

Week numbers range from 1 to 52 (and sometimes 53)

For example:

January 1, 2026 might fall in week 53 of the previous year depending on the calendar setup.

This system is often used in business, education, and data systems where consistent week identification matters.

🧮 How the Calculator Works

To find the week number:

Enter a date (e.g., 14 October 2025)

Click Calculate

The tool uses the ISO week algorithm and displays the correct week number of the year, such as Week 42.

This helps you place dates precisely within a yearly schedule.

📊 Why Week Numbers Matter

Week numbers are used in:

Project planning and tracking

Business reporting

School calendars

HR scheduling

Software systems and date analytics

They offer a consistent way to talk about time periods without specifying exact dates.

📍 Tips for Using the Week Number Calculator

Use the ISO standard system if collaborating with international teams.

Week numbers can span two years at the start/end of the calendar — check the year context.

Combine with other date tools (like the Date Calculator) for more planning flexibility.

⚠️ Important Notes

This calculator follows the ISO week date standard, which may differ from local or fiscal week definitions in some contexts.

Always match the week system (ISO vs. local) when comparing across calendars.