If you’re familiar with the desktop version of Word, you know you can use formulas to perform calculations such as summing a column or row of numbers in a table. Word Online preserves formulas already in your document, but it doesn’t yet provide a way to add them.
If you have the desktop version of Word, use the Open in Word command to open the document and insert the formula.
When you’re done and you save the document, it will continue to store the formula when you open it in Word Online.
To learn more, see Sum a column or row of numbers in a table in Word 2016 for Windows. If you don't have Word, you can try or buy it in the latest version of Office now.
Tip: Word Online works seamlessly with Word and other Office desktop programs, and we update it based on input like yours. For the latest feature announcements, visit the Office Online blog.