Week numbers 2026: complete calendar of all 53 weeks

You need a week number for a date in 2026. Maybe payroll runs on week numbers, your project board does, or a colleague in Europe just emailed asking you to ship by "week 14."

Here's the full list of week numbers for 2026, all 53 of them, with exact Monday-to-Sunday dates. Bookmark it, or print it and stick it on the wall.

And yes, 2026 has 53 weeks. Most years have 52, so the extra one catches people out. I'll explain why a bit further down.

The short answer#

2026 is a 53-week year under the ISO 8601 standard. Week 1 runs Monday December 29, 2025 to Sunday January 4, 2026. Week 53, the final week, runs Monday December 28, 2026 to Sunday January 3, 2027.

Every ISO week starts on a Monday and ends on a Sunday. The complete table of all 53 weeks sits in the next section.

All 53 week numbers in 2026#

Here's every ISO week of 2026 with its start and end date. Weeks run Monday to Sunday.

Three things worth pulling out of that table:

• Week 1 reaches back into December 2025. Its first three days (December 29 to 31) sit in 2025, but ISO counts them as part of week 1 of 2026.
• Week 53 spills into January 2027. Its last three days (January 1 to 3, 2027) belong to week 53 of 2026, not to 2027.
• That overlap at both ends is normal for the ISO system, and it's the reason the year ends up with 53 weeks.

Why does 2026 have 53 weeks?#

Most years have 52 weeks. 52 times 7 is 364, which leaves one or two days spare every year. Those leftover days slowly add up, and roughly every 5 or 6 years they push the count to 53.

ISO 8601 has a clean rule for when this happens. A year gets 53 weeks if January 1 falls on a Thursday, or if it's a leap year and January 1 falls on a Wednesday.

January 1, 2026 is a Thursday. So 2026 lands a 53rd week. December 31, 2026 is also a Thursday, which is the same rule seen from the other end of the year.

The previous 53-week year was 2020. The next one is 2032. If you want the full version of the math, I wrote it up on the weeks in a year page.

How ISO week numbers work#

ISO 8601 is the international standard for dates and times, and it defines how weeks get numbered. Three rules cover almost everything:

1. A week starts on Monday and ends on Sunday.
2. Week 1 is the week that contains the year's first Thursday.
3. Said another way, week 1 is the week that contains January 4.

That second rule is the one people miss. Because week 1 hangs on the first Thursday, the early days of January can land in the previous year's final week, and the last days of December can land in week 1 of the next year.

For 2026, the first Thursday is January 1 itself. That pulls the whole surrounding week (December 29 to January 4) into week 1. Full details of the standard live on the ISO week number guide.

ISO weeks vs the US week system#

Countries don't all number weeks the same way. The big split is between the ISO system, used across Europe and in most business and IT settings, and the US-style system you'll see on a lot of American wall calendars.

In practice, the same calendar date can carry two different week numbers depending on which system you use. If you're coordinating with someone in another country, it pays to check which one they mean before you commit to a deadline. For fiscal-year numbering, where the year doesn't even start in January, see the fiscal calendar tool.

Week numbers for key 2026 dates#

Want the week number for a single day without scanning the whole table? Here are the dates people look up most, with their ISO week.

For any other date, the fastest route is the week calculator. Type in a date and it returns the ISO week number, or go the other way and turn a week number back into its date range. To check which weekday a date falls on, the weekday calculator does that in one step.

How to find the week number for any 2026 date#

Three quick ways, depending on where you are.

If you just want the answer, use the week calculator linked above: enter a date, read the ISO week, or reverse it to get a week's date range.

In a spreadsheet, Excel and Google Sheets both have a built-in function:

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That returns 27, the week of US Independence Day in 2026.

By hand, find the Thursday of the week your date sits in, then count how many Thursdays have passed since the start of the year. That count is the ISO week number. It's fiddly, which is why most people reach for a calculator or a table like the one above.

FAQ#

Quick reference#

• Total ISO weeks in 2026: 53
• Week 1: Monday December 29, 2025 to Sunday January 4, 2026
• Week 53: Monday December 28, 2026 to Sunday January 3, 2027
• Convert any date to its week number: the week calculator
• Read more on the standard: the ISO week number guide

Sources#

• ISO 8601, Wikipedia
• ISO week date, Wikipedia
• ISO 8601 date and time format, ISO.org