Time & date
What Week Is It?
Today’s ISO week number is shown first, with its Monday–Sunday dates; below it are the US-style week number, a lookup for any date and a table of every week in the year.
Current week (ISO 8601)
Week —
Reading today’s date…
ISO weeks run Monday–Sunday and week 1 is the week with the year’s first Thursday — the standard in Europe, business and most software. The US count runs Sunday–Saturday and week 1 is whatever week holds January 1, so the two numbers are often one apart. Ask which system is meant when someone quotes a week number.
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Calculated in your browser from your device’s date and time zone.
Works in your browser. No account needed.
Frequently asked questions
What week is it right now?
The number at the top of this page is the current ISO 8601 week, worked out from your device’s date and time zone when the page loads, and refreshed if you leave it open past midnight. The Monday–Sunday range under it shows exactly which days that week covers.
What is the difference between the ISO and the US week number?
ISO weeks start on Monday and week 1 is the week containing the year’s first Thursday. The US count starts weeks on Sunday and makes week 1 the week containing January 1, even if that week has only one day of the new year. The two are often one apart, and the US count can reach week 53 or even 54, while ISO years always have 52 or 53 weeks.
Why is December 31 sometimes in week 1, or January 1 in week 53?
An ISO week belongs to the year that contains its Thursday. So 29–31 December can fall in week 1 of the next year (29 December 2025 is week 1 of 2026), and 1–3 January can fall in week 52 or 53 of the previous year (3 January 2021 is week 53 of 2020). The tool shows the ISO year next to every week number and points out when it differs from the calendar year.
Which years have 53 ISO weeks?
A year has 53 ISO weeks when it starts on a Thursday, or on a Wednesday in a leap year — for example 2015, 2020, 2026 and 2032. The year table shows 52 or 53 rows accordingly, and the header of the current week shows how many weeks this year has.
Is my date sent anywhere?
No. Everything is plain date arithmetic in your browser, using your device’s clock and time zone. Nothing is uploaded or stored, and the page keeps working offline once it has loaded.
About this tool
This page answers “what week is it?” the moment it opens. The large figure at the top is the current ISO 8601 week number, calculated in your browser from your device’s date and time zone, together with the ISO year it belongs to, how many weeks that year has, and the exact Monday-to-Sunday dates of the week. It also shows today’s day of the year, and it rolls over on its own if the page stays open past midnight.
Under it is the US-style week number, where weeks run Sunday to Saturday and week 1 is simply the week that contains January 1. Many American wall calendars and some spreadsheet functions count this way, which is why two people can quote different week numbers for the same day. ISO 8601 — used across Europe, in logistics, manufacturing and most business software — starts weeks on Monday and defines week 1 as the week containing the year’s first Thursday. The two systems usually differ by zero or one; when someone says “week 42”, it is worth confirming which one they mean.
The lookup box gives the ISO week, ISO year and US week for any date you pick, with the date ranges of both weeks and the day of the year. The ISO rule has edge cases at the turn of the year: 29–31 December can belong to week 1 of the next year and 1–3 January to week 52 or 53 of the previous one. For example, 31 December 2020 and 3 January 2021 are both in week 53 of 2020, and 28 December 2026 starts week 53 of 2026. Whenever a date’s ISO year differs from its calendar year, the tool says so and explains why.
The year table lists every ISO week of a year — 52 or 53 rows — with its Monday and Sunday dates, highlighting the current week and the week of the date you looked up. Use the arrows to move to the previous or next year for planning delivery weeks, sprints, school terms or payroll periods. Nothing leaves your browser.
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