Macros only survive in macro-enabled formats. Saving as .xlsx silently removes every module, so the first thing to do with a workbook that will hold code is Save As .xlsm.

Code

File > Save As > Excel Macro-Enabled Workbook (*.xlsm)

• Keep macros

  File > Save As > Excel Macro-Enabled Workbook (*.xlsm) → Code is kept with the file

  Do this before writing any code.

• Binary format

  Save As .xlsb → A binary macro-enabled file that is smaller and faster

  Good for large models with code.

• The warning

  Save As .xlsx by mistake → A warning appears; continuing strips the code

  Read the prompt.

• .xlsb loads faster and is smaller, but some tools cannot read it.
• Keep a .xlsm master even if you send .xlsx copies.
• Add-ins (.xlam) share macros across workbooks.

• Emailing an .xlsm often gets it blocked; zip it or share a link.
• Recipients must enable content before macros run.