Enter any date to find out which ISO 8601 week of the year it belongs to. The ISO standard is the one used across business, logistics and much of Europe, where weeks start on Monday and week one is the week containing the first Thursday of the year. That definition means a date in early January can belong to week 52 or 53 of the previous year, and this tool handles those edge cases correctly by also showing the ISO week year. Alongside the week number you get the day of the week and the Monday to Sunday date range that the week spans, so you can map a week number back to real dates. It defaults to today, updates as you change the date, and runs entirely in your browser.
It uses the ISO 8601 rule, where weeks start on Monday and week one is the week containing the first Thursday of the year.
Early January dates can belong to the last ISO week of the prior year, and late December dates can belong to week one of the next year, so the tool reports the correct week year.
Yes. It shows the Monday to Sunday date range for the ISO week alongside the number.
Enter any date to find out which ISO 8601 week of the year it belongs to. The ISO standard is the one used across business, logistics and much of Europe, where weeks start on Monday and week one is the week containing the first Thursday of the year.
Yes. ISO Week Number Calculator is completely free, with no sign-up and no usage limits.
Yes. ISO Week Number Calculator runs in any modern web browser. There is nothing to download or install.
Yes. ISO Week Number Calculator runs entirely on your device in your browser, so nothing you enter is uploaded to a server.