ISO week date explorer
Find the ISO week year, week number and weekday, including dates near New Year that belong to a different week year.
Your inputs
Start with the example values, then replace them with your own. For tables, keep the vertical bar separators and use a dot for decimals.
Calendar conventions can differ. This civil-date conversion does not determine legal deadlines or religious observance; verify those separately.
Tool inputs are processed in your browser and are not submitted by this tool. Existing site analytics and advertising services have their own privacy terms.
Result and workspace
Use the start button to open your result or activity.
How it works
ISO weeks start on Monday. Week 1 contains 4 January. The Thursday of the selected week determines its ISO week year.
Worked example
These sample results use the original example inputs in the form. They do not change when you edit your inputs; your own result appears in the workspace.
- ISO week year: 2026
- ISO week number: 1
- ISO weekday: 4
Read the result carefully
Results depend on the values and assumptions shown above. Change one input at a time to see its effect. A blank or unavailable result means the data does not support a calculation; it is not zero.