Excel, for some reason, keeps a memory of the calculation mode/status.

When you open the first workbook in a session, it uses the calculation mode set in that workbook and applies it to every other workbook. So, if the first workbook you open has the calculation mode set to manual, that's what it will use ... and it will retain the setting for the next Excel session.

Try setting the calculation mode to automatic before you save and close the workbook. And see what happens when you start another Excel session.

Regards, TMS