What week number is it today?

What week number is it today?

This page answers that question directly. It shows the current ISO week number, the ISO week year, today’s date, and the exact Monday-to-Sunday range for the current week. If you searched for “ISO week today”, “current ISO week number”, or “what number of week is it”, the main value at the top of the page is the answer.

The result is based on the current date in your browser, so there is nothing to enter manually. That makes the page useful for planning work by week, filling out forms, scheduling deliveries, or checking whether today falls in week 52, week 53, or week 1 of the next ISO week year.

What is a week number?

A week number identifies which week of the year a date belongs to. The most widely used standard is ISO 8601, which defines weeks as running Monday to Sunday. Week 1 is the week containing the first Thursday of the year, which means it is always the first week with at least four days in January.

Because of that definition, January 1 does not always fall in week 1. If the year starts on a Friday, Saturday, or Sunday, those days belong to the last ISO week of the previous year. Likewise, December 31 can fall in week 1 of the following ISO week year if it lands on a Monday, Tuesday, or Wednesday.

How to find the week number by date

If you need the week number for a specific date rather than today, use the linked week number calculator. Enter any date and it returns the ISO 8601 week immediately, along with the start and end dates of that week. This is the fastest way to check whether a deadline, invoice date, or event date belongs to a given week.

In practice, the rule is simple but easy to apply incorrectly by hand: weeks start on Monday, and counting begins from the week containing the first Thursday of the year. The calculator handles that logic directly, which is safer than counting weeks manually in a calendar.

Who uses week numbers?

ISO week numbers are standard in supply chain management, manufacturing, broadcasting, and project scheduling across Europe and in many international workflows. Weekly production plans, delivery schedules, broadcast calendars, and HR systems often reference weeks by number rather than by date range. Spreadsheet tools such as Excel and Google Sheets also expose WEEKNUM or ISOWEEKNUM functions that correspond to this kind of output.

Week numbers also appear in ERP systems, payroll cycles, and agricultural planning. Some US and Canadian systems use a different convention where week 1 simply begins on January 1, so the ISO and non-ISO methods can produce different answers near the start and end of the year.

ISO week number vs US week numbering

Many people assume there is only one current week number, but the answer depends on the numbering system. This page uses ISO 8601, the standard used across Europe and by many international systems. Under ISO, weeks start on Monday and week 1 is the week with the first Thursday of the year.

Some US calendars and software use a different rule, where week 1 starts on January 1 and weeks may begin on Sunday. That difference matters most near the year boundary. If a spreadsheet, payroll system, or reporting dashboard shows a different week number, verify whether it is using ISO week numbering or a US-style WEEKNUM convention.

Year boundary edge cases

The most confusing part of ISO week numbering is the year boundary. A late-December date can have a week year that is higher than its calendar year. For example, December 30, 2024 falls in ISO week 1 of 2025. Likewise, January 1, 2016 was in ISO week 53 of 2015. The week year shown on this page is the ISO week year, which can differ from the Gregorian calendar year for dates close to January 1 or December 31.