What week of the year is it?
Enter a date above and the tool gives the number along with the Sunday and Saturday that bound it. Today’s date is filled in by default, computed in your browser against your own clock rather than baked into the page.
Week Number
The week number for any date, and the days that week covers.
Week runs—
Weeks in this year—
Weeks start on Sunday, and week 1 is the one containing 1 January (US convention).
Two ways to number a week, and which one this page uses
In the United States a week runs Sunday to Saturday, and week 1 is simply the week containing 1 January. That is the convention applied above, because it is the one a US calendar, payroll system or retail planner will show you. It has the pleasant property that the week number never disagrees with the year printed on the date.
Most of the rest of the world numbers weeks by ISO-8601 instead, and it is a genuinely different system rather than a formatting preference. There the week runs Monday to Sunday, and week 1 is the week containing the year’s first Thursday — equivalently, the week containing 4 January. The consequence catches people out: 1 January 2027 falls on a Friday, so under ISO the 1st, 2nd and 3rd of January 2027 belong to week 53 of 2026. It runs the other way too — 31 December 2024 is a Tuesday sitting in week 1 of 2025.
That is why an ISO week number carries a year of its own, and why the year is part of the answer rather than decoration. A German colleague writing “KW 1” at the turn of the year may well mean days that fall in December. A year holds 52 or 53 ISO weeks — 53 when it starts on a Thursday, or when it is a leap year starting on a Wednesday — so 2026 has 53 while 2025 and 2027 have 52, and “week 53” without a year does not identify anything.
Frequently asked questions
Which week-numbering convention does this page use?
The US one: weeks run Sunday to Saturday and week 1 is the week containing 1 January. The other four languages on this site use ISO-8601, because that is the standard in the countries that read them. The tool states the convention it applied above the result so you never have to guess.
How does ISO-8601 number weeks?
Monday to Sunday, with week 1 being the week that contains the year’s first Thursday — the same as saying the week that contains 4 January. It is worth stating what this rules out: the week containing 1 January is not automatically week 1. If 1 January falls on a Friday, Saturday or Sunday, those days belong to the last week of the previous year.
Can a year have 53 weeks?
Yes, under ISO-8601. A year has 53 weeks when it begins on a Thursday, or when it is a leap year beginning on a Wednesday. 2026 is one of them; 2025 and 2027 each have 52. Because 52 weeks is only 364 days, the calendar has to give a 53rd week back every five or six years.
Why do two calendars show different week numbers for the same day?
Almost always because one is counting from Sunday with the US rule and the other from Monday with the ISO rule. Neither is broken. Check which convention each tool declares before assuming a bug — spreadsheet functions in particular take the convention as an argument, and the default is not the same everywhere.
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