Decreasing a cell value by one

This is the code that you need. Add this into the VBA editor under 'This Workbook' then go to Developer > Macros, select either one, press options and set a keyboard shortcut for each. The only issue is it has to be Ctrl and a letter, not a single key.

Sub AddOne()
ActiveCell.Value = ActiveCell.Value + 1
End Sub

Sub SubtractOne()
ActiveCell.Value = ActiveCell.Value - 1
End Sub