Penning trap measurements using mixed beams of 100Mo - 100Ru and 76Ge - 76Se have been utilized to determine the double-beta decay Q-values of 100Mo and 76Ge with uncertainties less than 200 eV. The value for 76Ge, 2039.04(16) keV is in agreement with the published SMILETRAP value. The new value for 100Mo, 3034.40(17) keV is 30 times more precise than the previous literature value, sufficient for the ongoing neutrinoless double-beta decay searches in 100Mo. Moreover, the precise Q-value is used to calculate the phase-space integrals and the experimental nuclear matrix element of double-beta decay.