How do you make a diagonal strike through line in a Microsoft Excel spreadsheet cell? If you're using Excel 2007 go to the home tab where you'll see the Format Numbers options area. There is a drop-down box which may be currently displaying "date". Click the arrow and select "More number formats." You'll see a bunch of tabs on the top of the pop up display. Go to the "border" tab. Select the diagonal line. This will insert a diagonal line from the lower left hand to the upper right hand corner of a cell, creating a "strike-through" effect if you will. Easy eh?