Cannot edit an Excel file in the browser

Short answer: Excel in the browser shows a file read-only when you are in view mode, when the file was shared as Can view, or when Protected View or a storage problem blocks saving. Check the Editing button first, then the sharing permission.

Check 1. You are in view mode

Microsoft's page on Excel for the web says: "you're probably in read-only view." The fix is one click. Microsoft says: "Select Editing." If the Editing button is missing or greyed out, go to check 2.

Check 2. The file was shared as Can view

When a file owner shares a workbook as read-only, the recipient cannot change it. Microsoft's sharing page says: "Select Can view to set the workbook as read-only." Ask the owner to change your link to a link that allows editing, or to give your account edit permission on the SharePoint library. Our advice, not a Microsoft rule: send the owner the file link and the exact words on the screen, so they can see which permission you have.

Microsoft also notes that read-only sharing "doesn't prevent someone from downloading a copy" and changing their own copy. A change in the copy does not reach the original.

Checks 3 to 5 come from Microsoft's page for the desktop apps. Use them if the file also opens read-only in desktop Excel.

Check 3. Protected View

Microsoft's read-only page says: "files from these potentially unsafe locations are opened in Protected View." Microsoft points to its "What is Protected View?" article for the settings.

Check 4. OneDrive is full

Microsoft's read-only page says: "you will be unable to save the document until you are under your allotted space." To check, select the OneDrive icon in the notification center and choose Manage storage. Or sign in at onedrive.live.com and look at the used space in the lower left.

Check 5. Office is not activated

Microsoft says the file can open read-only if "Microsoft 365 or Office isn't activated, or your Microsoft 365 subscription expired." The page points to its "Unlicensed Product and activation errors in Office" article.

Try the desktop app

For more advanced editing, Microsoft's page says: "For more advanced editing options, select Open in Desktop." Our advice, not a Microsoft rule: if the browser still blocks editing, open the file in the desktop app and see what message it gives.

Locked by another user

A different message says someone else has the file open. See "Excel file locked by another user".

When to get help

You can build all of this yourself in Microsoft 365. If you would rather have it built and tested for your team, I do that. A tracker like this is a fixed price: $5,000 for one, built in 2 weeks. See "What a SharePoint tracker costs to build". Bring one example of the problem to a free call.

Tell me what's still manual

I am Al Davies. I run 250 High Street LLC and build SharePoint trackers and Power Automate flows for operations teams. I work remotely. The first call is free, and I will not try to sell you anything.

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FAQ

Why can't I edit an Excel file in the browser?

You may be in view mode, or the file may be shared as Can view. Select Editing, then check the permission.

How do I switch from read-only to editing in Excel Online?

Microsoft says: "Select Editing."

Does a Can view link block all changes?

Microsoft says it sets the workbook as read-only. A person can still download a copy and change the copy.

Can a full OneDrive make a file read-only?

Microsoft says you cannot save the document until you are under your allotted space.

What does Open in Desktop do?

Microsoft's page lists it for more advanced editing options.