Expected Spot Rate

In the FCRP calculation, we calculate the Expected spot using Current Spot rate x (1+Idc)/(1+Ifc) using the inflation rate using PPP. I -> Inflation Can we use uncovered interest rate parity for doing this. I am confused when to use relative PPP and when to use uncovered PPP Uncovere Expected (Spot) = Current Spot rate x (1+rdc)/(1+rfc)