If cell is 0 or blank…

I have Microsoft Excel 2000. I can’t get a formula to work correctly for me. I am trying to create a formula in cell I13 that if D13 is 0 to leave I13 blank, if D13 is not 0 then to add I12 + D13. Does that make sense? I have done much research and thought that if I did: =IF(blank(D13,0,I12+D13)it would work, but it does not work. Any ideas? Thank you.