An　innovative　numerical　methodology　is　presented　for　fatigue　lifetime　estimation　of　notched　bodies　experiencing　multiaxial　cyclic　loadings.　In　the　presented　methodology,　an　evaluation　approach　of　the　local　nonproportionality　factor　F　for　notched　specimens,　which　defines　F　as　the　ratio　of　the　pseudoshear　strain　range　at　45　degrees　to　the　maximum　shear　plane　and　the　maximum　shear　strain　range,　is　proposed　and　discussed　deeply.　The　proposed　evaluation　method　is　incorporated　into　the　material　cyclic　stress-strain　equation　for　purpose　of　describing　the　nonproportional　hardening　behavior　for　some　material.　The　comparison　between　multiaxial　elastic-plastic　finite　element　analysis　(FEA)　and　experimentally　measured　strains　for　S460N　steel　notched　specimens　shows　that　the　proposed　nonproportionality　factor　estimation　method　is　effective.　Subsequently,　the　notch　stresses　and　strains　calculated　utilizing　multiaxial　elastic-plastic　FEA　are　used　as　input　data　to　the　critical　plane-based　fatigue　life　prediction　methodology.　The　prediction　results　are　satisfactory　for　the　7050-T7451　aluminum　alloy　and　GH4169　superalloy　notched　specimens　under　multiaxial　cyclic　loading.