Excel repair strips all formulas from large .xlsm after March 2026 security update (KB5002849)

Hellodjflobo​ 

Oh Boy I sure do not want to be in your shoes! But my suggestion is to switch to the .xlsb binary format of Excel. It seems to be better for large files. Not that it will not crash and ruin your day, but maybe less often.

I have seen plenty of great examples of Excel VBA code to backup your workbooks, and some are simply FANTASTIC!

I suggest you start rebuilding the workbook from a clean up, and then Utilize the .xlsb file format with the VBA code that would automatically make a backup as you open the workbook. Some code exmples out there also prompt you to delete old versions of the workbook.

And yes, one of the options in recovery is to recover the data by fixing all the formulas to their values.

Try safe mode and see if the Repair process does not trigger.

and yes Excel for Windows and the Mac should be identical in terms of functionality. Try an unpatched version and see if you can make 25 backups 🤪 but try the local library that may have PCs for the public to use. Here in the USA, most public libraries have computers for the public to use.

I’m don’t have any information about size. But it’s been an issue from Excel’s day one! The XML format did help, but a little…

As you are searching for the backup code, also search for the code that would list all the Conditional Formatting rules and see if you have duplicate rules. Sometimes Excel makes these duplicate rules when you copy/paste data. Cleaning these will make your workbook smaller and perform better.

several years back, I started a project to rebuild a workbook and I got a lot done, but then abandoned this project for some reason or another. Maybe I’ll dig up the code and try again.

Keep us posted as to your progress.