A simple approach for analyzing electron transfer (ET) reactions is proposed based on energy decomposition and extrapolation schemes. The present energy decomposition and extrapolation-based electron localization (EDEEL) method represents the diabatic energies for the initial and final states using the adiabatic energies of the donor and acceptor species and their complex. A scheme to estimate ET rate constants efficiently is also proposed by combining it with the Marcus theory. EDEEL is semi-quantitative by directly evaluating the seam-of-crossing region of two diabatic potentials. In a numerical test, EDEEL successfully provided ET rate constants for electron self-exchange reactions of thirteen transition metal complexes with reasonable accuracy. Furthermore, its energy decomposition and extrapolation schemes give all the energy values required in the activation strain model (ASM) analysis. The ASM analysis using EDEEL provided rational interpretations of the variation of the ET rate constants depending on the transition metal complexes. Its extension combining two computational levels was discussed to further reduce its computational costs. These results suggest that EDEEL is useful in efficiently evaluating ET rate constants and obtaining a rational understanding of their magnitudes.