Adding up columns or rows of numbers is one of the most commonly performed actions in Excel. The SUM function provides a quick and easy way to carry out this task in an Excel worksheet.
These instructions apply to Excel for Microsoft 365, Excel 2019, 2016, 2013, 2010, Excel 2019 for Mac, Excel 2016 for Mac, Excel for Mac 2011, and Excel Online.
The SUM Function Syntax and Arguments
A function's syntax refers to the layout of the function and includes the function's name, brackets, and arguments.
The syntax for the SUM function is:
=SUM(Number1,Number2,...Number255)
Number1 (required) is the first value to be summed. This argument can contain the data you want to sum up, or it can be a cell reference to the location of the data in the worksheet.
Number2, Number3, ... Number255 (optional) is the additional values to be summed up to a maximum of 255.
Sum Data in Excel Using Shortcut Keys
The key combination to enter the SUM function is:
Alt+=
Here's how to input the SUM function using the shortcut keys:

Select a cell for the sum and then press and hold down the Alt key on the keyboard.

Press and release the equal sign (=) on the keyboard without releasing the Alt key.

Release the Alt key. The SUM function appears within the active cell with the Insertion point or cursor located between a pair of empty round brackets. The brackets hold the function's argument (the range of cell references or numbers to be summed).

Enter the function's argument:
 Using pointandclick with the mouse to enter individual cell references,
 Using clickanddrag with the mouse to highlight a contiguous range of cells, or
 Typing the numbers or cell references manually.

After you've entered the argument, press the Enter key on the keyboard to complete the function. The answer will appear in the cell containing the function. When you select that cell, the completed SUM function appears in the formula bar above the worksheet.
Speed up data entry by inputting individual cells and cell ranges correctly:
 Separate individual cell references entered by typing or pointing with commas.
 For a range of cell references entered by typing, you can separate the starting and ending point cell references with a colon.
Sum Data in Excel Using AutoSUM
Use the AutoSUM shortcut located on the Home tab of the ribbon to complete the formula without having to type.
The "Auto" part of the name AutoSUM refers to the method automatically selecting what it believes is the range of cells to be summed by the function. The selected range has shading and an animated border known as "marching ants."
The AutoSUM function should be input at the bottom of a column of data or the right end of a row of data. If you put the AutoSUM function in another spot on the spreadsheet, the range of cells selected as the function's argument may be incorrect. To change the selected range, use the mouse pointer to highlight the correct range before pressing the Enter key to complete the function
To use AutoSUM:

Select the cell where you want the result to display and click the AutoSUM icon on the ribbon.

Check to see that the selected range, which will form the function's argument, is correct.

If it's accurate, press the Enter key on the keyboard to complete the function. The answer will display in the cell.

When you click on the cell containing the solution, the completed SUM function appears in the formula bar above the worksheet.
Using the SUM Function Dialog Box
You can enter most functions in Excel using a dialog box, which allows you to input the arguments for the function on separate lines. The dialog box also takes care of the function's syntax, such as the opening and closing parentheses and the commas used to separate individual arguments.
Although individual numbers can be entered directly into the dialog box as arguments, it is usually best to enter the data into worksheet cells and enter the cell references as arguments for the function.
To enter the SUM function using the dialog box in Excel 2019, 2016, 2013, 2010, or Excel for Mac:

Select the cell where the results will be displayed.

Select the Formulas tab of the ribbon menu.

Choose Math & Trig from the ribbon to open the function dropdown list.

Select SUM in the list to bring up the function's dialog box.

Select the Number1 line in the dialog box.

Highlight at least one cell reference or a range of references.

Choose OK to complete the function and close the dialog box.
To enter the SUM function in all versions of Excel, including Excel Online:

Select the cell where the results will be displayed.

Select Insert Function to open the Insert Function dialog box.

Select Math & Trig in the Category list.

Select SUM in the list to bring up the function's dialog box.

Select OK.

Highlight at least one cell reference or a range of references.

Press Enter to complete the function
The answer will appear in the selected cell, and the SUM function formula will display in the formula bar.