Current Week Number
See today's ISO 8601 week number and the US/Excel week number, the Monday-to-Sunday dates the current week covers, and how many weeks are left in the year. The live tool below updates every second using your device's clock and time zone.
What Is the Current Week Number?
The current week number counts which week of the year it is: Week 1 at the start of January, Week 52 or 53 at the end of December. The live display above reads your device's date and shows the ISO 8601 week number, the dates that week covers, and a US/Excel week number underneath, because the two systems often disagree.
Week numbers are used in project management, manufacturing, payroll, and academic scheduling. Saying "Week 11" instead of "the second week of March" names one exact week and cannot be misread across years.
How to Calculate Which Week of the Year It Is
A quick method many people use is to count the days since January 1st, divide by 7, and round up. It is easy to do in your head, but it does not match ISO 8601, the international standard this tool uses.
ISO 8601 weeks run Monday to Sunday, and Week 1 is the week that contains the year's first Thursday, which is the same as the week containing January 4th. When January 1st falls on a Monday, Tuesday, Wednesday or Thursday, it is part of Week 1, so Week 1 can start in late December (December 29 to 31). When January 1st falls on a Friday, Saturday or Sunday, those first days still belong to the last week of the previous year, and Week 1 starts on January 4th, 3rd or 2nd.
The week number shown here matches the Week Numbers Calendar for the same date, since both use the same ISO calculation.
Sunday vs Monday: When Does a Week Start?
ISO 8601, and most of Europe, start the week on Monday. In the United States calendars conventionally start on Sunday, and the week-numbering system built into Excel's WEEKNUM function (with its default setting) follows that: weeks start on Sunday and Week 1 is the week that contains January 1st.
The two systems give different numbers. In 2026, January 1st is a Thursday. Sunday, October 18, 2026 is ISO Week 42 (it is the last day of the week that began on Monday, October 12), but it is Week 43 in the US/Excel system, because a new Sunday-start week begins that day. From Monday to Saturday of the same week, both systems give 42. The page shows both, so you can use whichever your team or spreadsheet uses.
The US/Excel system is a spreadsheet convention rather than a single official standard, and other organisations define week 1 differently. What matters is that everyone on a project uses the same system: mixing ISO and US week numbers in a shared file is an easy way to schedule something a week off.
Why Week Numbers Matter in Business
Planning by week number is a common habit in manufacturing and logistics. A production schedule that says "deliver by Week 24" avoids any argument about whether "early June" means the 3rd or the 10th.
In software teams, sprints and release targets are often expressed in weeks, and weekly reports (active users, revenue by week) use week numbers to compare one period with the same period last year.
Payroll and HR teams also use week numbers when pay periods or leave are tracked by week. The one thing to check is which numbering system your organisation uses, since the ISO and US numbers can differ by one.
Frequently Asked Questions
What week number is it right now?
The live tool above shows today's week number from your device's date. It gives the ISO 8601 number, and the US/Excel number underneath. Weeks are numbered 1 to 52, or 53 in some years.
How is the current week number calculated?
The main number follows ISO 8601: weeks run Monday to Sunday and Week 1 is the week containing the year's first Thursday (the week with January 4th). The US/Excel number counts Sunday-start weeks, with Week 1 being the week that contains January 1st. The two can differ by one, and the pattern depends on which weekday January 1st falls on.
How many weeks are left in the year?
Subtract the current ISO week number from the number of weeks in the year (52, or 53 in a 53-week year). In Week 22 of a 52-week year, there are 30 weeks left after the current one. The tool above shows this number for you.
Does the week start on Sunday or Monday?
ISO 8601 and most of Europe use Monday. In the United States, calendars conventionally start the week on Sunday, and Excel's default WEEKNUM does too. This page shows both numbers so you can see the difference.
What is a 53-week year?
In the ISO system, a year has 53 weeks when January 1st is a Thursday, or when it is a leap year starting on a Wednesday. Week 53 is a full Monday to Sunday week that usually straddles December and January: Week 53 of 2026 runs from December 28, 2026 to January 3, 2027. It happens roughly every five to six years.
Why does this page show a different week number from my Excel sheet?
Excel's WEEKNUM defaults to the US system (Sunday start, Week 1 contains January 1st), while this page leads with the ISO number. Use WEEKNUM(date, 21) or ISOWEEKNUM(date) in Excel to get the ISO number, or read the US/Excel line on this page.