A method for calculating effective cadmium cutoff energies to be applied to measured resonance integrals of Doppler-broadened-resonance absorbers, as well as l/υ absorbers, is described. The method is applied to infinite slab, infinite cylinder, and sphere configurations in which the absorber, at some uniform concentration, occupies all the space within the cadmium cover. It is pointed out that the effective cutoff value applying to an activation measurement of a resonance integral differs from that applying to a reactivity measurement under otherwise identical conditions. The development of calculations for both cases is presented. Some results are given for gold, indium-115, plutonium-240, and the l/υ absorbers, boron and vanadium, as a function of sample configuration, cadmium thickness, absorber density, temperature, and neutron spectrum. Many of these values differ significantly from the nominal 0.5 eV.