What week is it?

How ISO week numbers work

Under ISO 8601, weeks run Monday to Sunday, and week 1 is the week containing the year's first Thursday (equivalently, the week of 4 January). That means up to three days of early January can belong to the previous year's final week — 1 January can be in week 52 or 53 — and years have either 52 or 53 weeks.

Beware: the US convention (weeks start Sunday, week 1 contains 1 January) gives different numbers, which is why "week 32" can mean different things in different companies. When it matters, say "ISO week 32" and everyone can check a date. Planning that week's meeting across offices? Use the planner.