ISO Week Converter: Date, Week Year & Week Number
Convert Gregorian dates to ISO week dates and back, showing Monday–Sunday ranges and validating week 53 at year boundaries.
Enabling local controls…
1. Date and ISO week
Calculated in page memory. ISO weeks start Monday; week 1 contains January 4. The week-year can differ from the calendar year.
Years 0001–9999; strict 10-character format. No regional or fiscal week rules. Complete weeks outside this range are rejected.
2. Result
Enter a date or load the year-boundary sample, then convert.
How to use this tool
Enter a calendar date or an ISO week year, week and weekday. Convert and inspect the complete week range; the week year may differ from the calendar year.
When not to use it
ISO weeks start Monday and week 1 contains January 4. This is not a fiscal, locale-specific or Sunday-first week system.
Read the guide →