Currency Forward Valuation

Could someone give me the formula to value currency forwards?

St/(1+rf)^(T-t) - F/(1+rd)^(T-t)

St and F are specified as DC/FC

T=Original term of contract (6 months forward)

t = now (say 2 months later)


qualitiativley the price of a forward is set at the price which allows the currency with the higher interst rate to depreciate by the difference in the 2 interest rates.