How it works
Find the ISO weekday number for a Gregorian calendar date. Monday is 1 and Sunday is 7, independent of local timezone.
ISO weekday: Monday = 1, Sunday = 7
Worked example
Show example inputs and result
Calendar date: October 8, 2026.
- ISO weekday number
- 4
Questions and answers
Why are some results rounded?
Results display up to 8 decimal places. Calculations use the unrounded values; very small values use scientific notation. JavaScript floating-point arithmetic can introduce tiny rounding differences.
Are my inputs sent to a server?
The calculator processes inputs in your browser. Its code does not send your values to a server.
Method reviewed: October 8, 2026 · Methods & accuracy