How to Get a Date From a Week Number in Excel
By ExcelReady TeamUpdated 7 min read
The short answer
Excel has no single function for this, so build the date with DATE and WEEKDAY. With the year in B1 and the ISO week number in B2, =DATE(B1,1,4)-WEEKDAY(DATE(B1,1,4),2)+1+(B2-1)*7 returns the Monday that starts that week. For 2026 week 10, that is Monday 2 March 2026. Add 6 to get the Sunday that ends it.
Key takeaways
- Excel can turn a date into a week number, but there is no built-in function for the reverse.
- For ISO weeks, start from 4 January, which is always in week 1, step back to its Monday, then add 7 days per week.
- For WEEKNUM-style weeks, start from 1 January instead, because week 1 is the week that contains it.
- The ISO and WEEKNUM systems can give dates a full week apart, so check which one your data uses.
- Add 6 to the start date to get the last day of the week.
On this page+
To get a date from a week number in Excel, build it from the start of the year: find the first day of week 1 with DATE and WEEKDAY, then add 7 days for every week after that. With the year in B1 and an ISO week number in B2, =DATE(B1,1,4)-WEEKDAY(DATE(B1,1,4),2)+1+(B2-1)*7 returns the Monday of that week. This guide is for anyone whose reports, plans or system exports give week numbers but need real dates, and it covers both week-numbering systems.
Why Excel needs a formula for this#
Excel can go from a date to a week number with WEEKNUM or ISOWEEKNUM, but no function goes back the other way. A week number alone is also not enough: you need the year, and you need to know which system the number uses.
There are two common systems, explained fully in the guide to getting the week number from a date:
| System | Week starts | Week 1 is | Function that matches |
|---|---|---|---|
| ISO | Monday | The week that contains the first Thursday of the year (so it always contains 4 January) | ISOWEEKNUM |
| WEEKNUM | Sunday (type 1) or Monday (type 2) | The week that contains 1 January | WEEKNUM |
ISO weeks are standard in much of Europe and in many planning systems. US reports often use WEEKNUM's Sunday weeks. If you are unsure, ask where the numbers come from.
How to get the Monday of an ISO week number#
Use 4 January as your anchor, because it always falls in ISO week 1. Put the year in B1 and the week number in B2, then type:
=DATE(B1,1,4)-WEEKDAY(DATE(B1,1,4),2)+1+(B2-1)*7For 2026 and week 10, the result is Monday 2 March 2026. If you see a number such as 46083, format the cell as a date (Home > Number Format > Short Date). Excel stores dates as serial numbers; the date basics lesson explains why.
Here is what each part does:
| Part | Meaning | 2026 result |
|---|---|---|
DATE(B1,1,4) | 4 January of the year | Sun 4 Jan 2026 |
WEEKDAY(DATE(B1,1,4),2) | Its weekday, with Monday = 1 and Sunday = 7 | 7 |
DATE(...)-WEEKDAY(...)+1 | Step back to that week's Monday: the start of week 1 | Mon 29 Dec 2025 |
+(B2-1)*7 | Add 7 days for each week after week 1 | + 63 days |
The 2 in WEEKDAY matters. Without it, WEEKDAY counts Sunday as 1, and the formula lands on the wrong day.
Notice that ISO week 1 of 2026 starts in December 2025. That is normal: the week belongs to 2026 because most of its days do.
How to get a date from a WEEKNUM week number#
WEEKNUM counts the week that contains 1 January as week 1, so use 1 January as the anchor instead. For weeks that start on Sunday (WEEKNUM's default, type 1):
=DATE(B1,1,1)-WEEKDAY(DATE(B1,1,1))+1+(B2-1)*7For weeks that start on Monday (WEEKNUM type 2):
=DATE(B1,1,1)-WEEKDAY(DATE(B1,1,1),2)+1+(B2-1)*7In 2026, 1 January is a Thursday, so week 10 starts on Sunday 1 March or Monday 2 March. The Monday result matches the ISO formula this year, but not every year.
When ISO and WEEKNUM weeks give different dates#
The two systems differ when 1 January falls on a Friday, Saturday or Sunday. Then ISO week 1 starts after New Year, while WEEKNUM week 1 starts before it. In 2027, 1 January is a Friday:
| Week 10 of 2027 | Formula anchor | Week starts |
|---|---|---|
| ISO | 4 January | Mon 8 Mar 2027 |
| WEEKNUM type 2 (Monday) | 1 January | Mon 1 Mar 2027 |
| WEEKNUM type 1 (Sunday) | 1 January | Sun 28 Feb 2027 |
The same "week 10" is a full week apart. Using the wrong system shifts every weekly total, so check by wrapping your result: =ISOWEEKNUM(B4) or =WEEKNUM(B4,2) should give back the week number you started with.
ISO years can also have 53 weeks. 2026 is one of them: ISO week 53 starts on Monday 28 December 2026.
How to get the end date of a week#
The last day of a week is 6 days after its first day. Add 6 to any of the formulas:
=DATE(B1,1,4)-WEEKDAY(DATE(B1,1,4),2)+1+(B2-1)*7+6For ISO week 10 of 2026, this returns Sunday 8 March 2026. If your reports label weeks by their last day, the guide to finding the week ending date shows the reverse: from any date to its Friday or Sunday.
To keep week 1 inside the year, so it starts no earlier than 1 January, wrap the start date in MAX:
=MAX(DATE(B1,1,1),DATE(B1,1,1)-WEEKDAY(DATE(B1,1,1),2)+1+(B2-1)*7)For week 1 of 2026 this returns Thursday 1 January 2026 instead of Monday 29 December 2025. Later weeks are not affected.
How to convert a label like 2026-W10 into a date#
Exports often store the year and week together as text. Pull the parts out with LEFT and RIGHT and put them into the same formula. With 2026-W10 in A2:
=DATE(LEFT(A2,4),1,4)-WEEKDAY(DATE(LEFT(A2,4),1,4),2)+1+(RIGHT(A2,2)-1)*7LEFT(A2,4) returns "2026" and RIGHT(A2,2) returns "10". Excel turns the text into numbers inside DATE and the subtraction, so the result is again Monday 2 March 2026. This works when the week always has two digits, as in W03. For other ways to shift dates by days, weeks and months, see adding days, months and years and the overview of Excel date functions.
Common mistakes#
These cause most wrong week dates:
- Leaving out the 2 in WEEKDAY. The default counts Sunday as 1 and moves the result by a day.
- Using the wrong anchor. 4 January is for ISO weeks; 1 January is for WEEKNUM weeks.
- Forgetting the -1. Week 1 adds zero weeks, so it is
(B2-1)*7, notB2*7. - Mixing years. Late-December dates can belong to week 1 of the next ISO year. Always keep the year with the week.
- Reading the result as a number. Format the cell as a date.
Practise it#
This formula is just date arithmetic: dates are numbers, and WEEKDAY tells you where you are in the week. Practise date basics in a live spreadsheet, then practise EDATE, EOMONTH and WEEKDAY: you type the formula and it checks it instantly. Or try the exercise on this page and find the Monday of ISO week 10.
Try it yourself
This is a live spreadsheet. Type the formula in the green cell and press Enter.
Find the Monday that starts ISO week 10 of 2026. In B4, start from 4 January of the year in B1, step back to its Monday with WEEKDAY(...,2), then add 7 days for each week after week 1 (the week number is in B2). Press Enter.
| A | B | C | D | |
|---|---|---|---|---|
| 1 | ||||
| 2 | ||||
| 3 | ||||
| 4 | Week starts | |||
| 5 | ||||
| 6 | ||||
| 7 |
Tip: DATE(B1,1,4) is 4 January. Subtract WEEKDAY(DATE(B1,1,4),2) and add 1 to reach Monday, then add (B2-1)*7.
Practise this in a lesson
Frequently asked questions
How do I convert a week number to a date in Excel?
Use DATE and WEEKDAY. For ISO weeks, =DATE(B1,1,4)-WEEKDAY(DATE(B1,1,4),2)+1+(B2-1)*7 returns the Monday of week B2 in year B1. Format the cell as a date.
How do I get the start and end date of a week number in Excel?
Calculate the start date with the DATE and WEEKDAY formula, then add 6 for the end date. For a Monday start, the end date is the Sunday six days later.
Why is my week 1 date in December?
Week 1 often starts in the previous year. In 2026, ISO week 1 starts on Monday 29 December 2025, because 1 January 2026 is a Thursday. Use MAX with DATE(year,1,1) if you want week 1 to start no earlier than 1 January.
Is there an Excel function that returns a date from a week number?
No. WEEKNUM and ISOWEEKNUM go from a date to a week number only. You build the reverse with DATE, WEEKDAY and a little arithmetic.
How do I check that my week number formula is right?
Wrap the result in ISOWEEKNUM or WEEKNUM, whichever system you used. It should return the week number you started with.