CalculationTime

Calendar Week Converter

A printable converter for ISO week dates, Sunday-start calendar weeks, week boundaries and date labels beside the CalculationTime clockface.

Time Duration Calculator

Week Converter

Convert dates and week labels

ISO week date
Sunday-start week

Selected date

26 July

Sun, 26 July 2026 converts to 2026-W30-7
ISO week
2026-W30
ISO range
20 July-26 July
Sunday week
Week 31
Sunday range
26 July-01 Aug
2026-W30-7ISO week-date for selected date
2026-W30-7Reverse ISO lookup lands on Sun, 26 July 2026
2026 Sunday week 31, day 1Sunday-start label for selected date
2026 Sunday week 31, day 1Reverse Sunday-start lookup lands on Sun, 26 July 2026
  1. Monday2026-W30-120 July
  2. Tuesday2026-W30-221 July
  3. Wednesday2026-W30-322 July
  4. Thursday2026-W30-423 July
  5. Friday2026-W30-524 July
  6. Saturday2026-W30-625 July
  7. Sunday2026-W30-726 July

Conversion check

Sun, 26 July 2026 is ISO weekday 7, inside ISO week 30 of 2026. The same date is day 1 of Sunday-start week 31 in 2026.

Week boundaries

ISO week range: Mon, 20 July 2026 to Sun, 26 July 2026. Sunday-start range: Sun, 26 July 2026 to Sat, 01 Aug 2026.

Input limits

ISO year 2026 has 53 ISO weeks. Sunday-start year 2026 has 53labelled weeks under this page's January 1 rule.

Notes

Use this report for release planning, editorial calendars, roster labels and any handoff where ISO week numbers need a civil-date check.

Method

Week labels depend on the week system you choose

ISO 8601 weeks start on Monday and week 1 is the week containing the first Thursday of the ISO week-year. The Sunday-start comparison labels week 1 as the week containing January 1, with each week running Sunday to Saturday.

ISO conversion

The date is moved to the Thursday of its week, then compared with the first Thursday week of that ISO year to find the week number.

Reverse lookup

ISO week-year, week and weekday inputs are converted back to the Monday-start week range and selected civil date.

Limits

The tool uses local Gregorian calendar dates at noon. It does not claim payroll, school, fiscal or regional compliance rules.

Source Notes

ISO week dates use the published ISO 8601 convention

ISO 8601 defines week dates around Monday-start weeks and week-years. Browser date objects provide the local Gregorian date stepping used for the on-page calculations.

ReferencesISO 8601 date and time formatECMAScript Date objects