ISO Week Calculator
ISO 8601 week dates, both directions
A date to its ISO week-date form and back — `2024-W29-2` — with the ISO year, which is not always the calendar year.
Questions people ask
The things that come up about iso week calculators, answered plainly.
What is an ISO week date?
A date written as year, week and weekday: 2024-W29-2 is Tuesday of week 29 of 2024. It is a fully valid ISO 8601 date form, and it is what many manufacturing, logistics and payroll systems run on.
Why is 31 December sometimes in the next year's week 1?
Because ISO weeks belong to the year containing their Thursday. If 31 December is a Monday, Tuesday or Wednesday, its week's Thursday is already in January — so the date sits in week 1 of the following ISO year.
Related tools
Printable calendars, week numbers, quarters, fiscal years and weekday finders.
Week Number CalculatorThe ISO week for any date, the US week beside it, the Monday-to-Sunday dates the week covers, and how many weeks the year has.
Calendar Week FinderEnter a week number and a year, get the seven dates it covers — and the reverse, a date to its week — with both the ISO and US conventions.
ISO Date ConverterThe extended form, the basic form, the week date and the ordinal date — all four ISO 8601 shapes for one instant, plus a parser for reading them back.
Weekly CalendarSeven days with their dates, week number, and the hours of the day down the side — a week planner you can print or share as a link.