What week-number convention does this calculator use?
It uses ISO 8601 week dates: weeks start on Monday and week 1 is the week containing January 4.
Why can the ISO week-year differ from the calendar year?
Dates near New Year can belong to the final ISO week of the previous week-year or the first ISO week of the next week-year.
What dates are shown for the week?
The result includes the Monday start and Sunday end of the selected ISO week.
Is this the same as every U.S. calendar week number?
No. Some calendars use Sunday starts or define week 1 differently. This page explicitly uses ISO week numbering.
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Frequently asked questions
No. ISO week 1 is the week containing January 4.
Monday.
Yes. ISO week-year boundaries can differ from calendar-year boundaries.
Yes.
Yes. It shows Monday through Sunday.
Not necessarily. Employer pay periods can use different schedules.
No. The input is a calendar date.
The page uses the ISO 8601 week-date convention.
Sources and methodology
This calculator uses transparent browser-side date/time arithmetic. The references below provide standards or official context relevant to the calculation.
ISO — ISO 8601 date and time formatInternational standard context for unambiguous Gregorian dates, times, UTC and intervals.ISO — ISO 8601-1:2019Current published ISO standard for Gregorian date and time representations.
Date and time scope: Calendar, time-zone, holiday and scheduling conventions can differ by jurisdiction or organization. Check authoritative rules when a deadline, legal right, payroll event or travel schedule depends on the exact result.
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