Just like the Word desktop program, Word Online counts words while you type.
If you don’t see the word count at the bottom of the window, make sure you’re in Editing view (click Edit Document > Edit in Word Online).
Click the word count to switch it off and on.
Maybe you noticed that Word Online gives you an approximate word count. That’s because it doesn’t count words in areas like text boxes, headers, footers, and SmartArt graphics. If you need an exact count, click Open in Word, and look at the word count at the bottom of the Word window.