This is the correct behaviour, =SUM(A1) should give you A1 in both Excel and Google Sheets. You are passing in a single cell into SUM, so only asking it to add

This is the correct behaviour, =SUM(A1) should give you A1 in both Excel and Google Sheets. You are passing in a single cell into SUM, so only asking it to add that cell up (not the cells below). You must refer to a range of cells for it to work - in Excel this would be for instance =SUM(A:A). In Google Sheets: generally you write a formula and hit Ctrl+Shift+Enter which will turn it into an array formula. In Excel there are many more options in how to handle this, one of which is to define a table in Excel (Insert -> Table) and then refer to the table and column (=TableName[Column]).