Add or subtract date/time
Add or subtract date/time lets you add calendar and clock units with explicit time zone and month-end constrain policy in your browser.
ISO week number
ISO week number lets you calculate ISO week, week-based year, and week range from a date in your browser.
ISO week number
⌂ Inputs and results stay in this browser and are not automatically stored or sent.
Waiting for input
Input
Output
Waiting for input
Complete text result
How to use
Enter a date to inspect its ISO week number, week-based year, and date range. Supply the week-based year when converting a week back to dates.
Near New Year, the calendar year can differ from the week-based year. Identify a week by both year and number, not the number alone.
Examples
2026-01-01Principles and limits
Each input is limited to 1,048,576 bytes, output to 33,554,432 bytes, and processing to 5,000 ms. Input is never silently truncated.
Guides
Related tools
Business day calculator
Business day calculator lets you count inclusive business days excluding chosen weekdays and entered holidays in your browser.