FireCalc Fixed Return entries?

[ShokWaveRider]

We only have fixed rate returns and laddered CDs as investments. I am not sure how to enter these into firecalc. Does one Zero out stocks? Then put say 4% average (or whatever) fixed income return for the complete portfolio?

OR, simply not use It and just go to one of the "How Long Will My Money Last" calculators?

TIA.