Thechangesofnumerairecanbeusedasaverypowerfultoolinpricingcontingentclaimsinthecontextofacompletemarket.Byusingthemethodofnumerairechangestoevaluateconvertiblebondswhenthevalueoffirm,andthoseofzero-couponbondsfollowgeneraladaptedstochasticprocessesinthispaper,usingItotheoremandGisanovtheorem.Aclosed-formsolutionisderivedunderthestochasticvolatilitybyusingfastFouriertransforms.