ISO Week Number Calculator

Find the ISO 8601 week-year and week number for a valid calendar date using UTC date arithmetic.

About this tool

Find the ISO 8601 week-year and week number for a valid calendar date using UTC date arithmetic. Use values in the units specified by each field and check the assumptions in the result before applying it. The included example demonstrates how the calculation is interpreted. Invalid dates, denominators, and out-of-range values are rejected. Inputs are processed locally in the browser; this utility does not connect to a financial account or external data source.

How to use this tool

  1. Enter the values in the labeled units.
  2. Check the assumptions and dates.
  3. Run the calculation and review the result.

How it works

ISO Week Number Calculator applies the named formula or calendar rule to your inputs and returns a readable result.

When to use this tool

  • Quick iso week number calculator estimates
  • Local calculations without uploading input values

Limitations

The ISO Week Number Calculator outputs are estimates and its calendar calculations do not incorporate jurisdiction-specific holidays unless stated.

Privacy

The inputs and results of ISO Week Number Calculator remain in browser memory and are not uploaded by this tool.