Week Number

The week number is a way to label weeks in a year (for example, “week 05”). This tool shows the current ISO week number and ISO year for today.

This calculator follows ISO 8601: weeks start on Monday, and week 1 is the week that contains January 4th. That means the first days of January can sometimes belong to the last ISO week of the previous year.

• Use Week number of a date to pick a calendar date and see its ISO week number.
• Use Week number to date range to convert an ISO year + week into the Monday–Sunday date range.
• Use this when you’re planning sprints, comparing reports, or scheduling by week number.

The tool is ISO-only for consistency. If you need weekday counts between dates, use the date calculator.

If you use week number often, bookmark this page or pin it as a shortcut so it’s always one tap away. For the best experience, keep the tab open and interact with the controls once so your browser allows audio alerts, permission prompts, or full-screen mode when needed.

For presentations, classrooms, or a second monitor, try full-screen mode. It centers the tool and removes distractions, and the zoom buttons let you fit the display to your viewing distance.

Browsers can throttle timers in background tabs to save battery. These tools keep accurate time by calculating against a stable clock, so even if the UI updates less frequently, the underlying time stays correct when you return.

Many pages are preset links. Sharing the URL is the fastest way to open the same configuration on another device, whether that’s a timer duration, a specific alarm time, or a countdown to an event year.

Your preferences (like theme and alarm sound) are stored locally in your browser. There’s no login required, and nothing needs to be uploaded for the tools to work.