Short answer
Convert a week number to dates
Find the Monday and Sunday of a valid ISO calendar week.
ISO notation
Inputs are calendar dates without a time. ISO classification is therefore independent of the device time zone.
Short answer
An ISO week-year and week number identify one seven-day period.
How it works
Week 1 contains 4 January; every later week is counted from that week’s Monday.
A week needs its ISO year
Week 1 without a year does not identify a date range. Use the ISO week-year even when Monday falls in the preceding calendar year. 2026-W01 runs from 29 December 2025 to 4 January 2026.
2026-W53 runs from 28 December 2026 to 3 January 2027; 2027-W53 does not exist. Share the Monday–Sunday dates with the week ID. A week range alone does not specify a deadline or time zone. ICS uses an exclusive end date after the visible Sunday.