The Butler-Volmer equation was reformulated to describe the dependent of charge-transfer resistance (Rct) on current density, showing that Rct is constant for I < I0, but decreases logarithmically with current at I > I0. Expressions were derived for the differential charge-transfer resistance (𝑅 𝑐𝑡 ′ ), which is the local slope of the overpotential-current curve at the applied current, and for the linearized charge-transfer resistance (𝑅 𝑐𝑡 0 ), which is the limit of 𝑅 𝑐𝑡 ′ as the current approaches zero. For a symmetric one-step reaction, it was shown that Rct and 𝑅 𝑐𝑡 ′ both follow universal dimensionless relationships between normalized resistance (𝑟 = 𝑅 𝑐𝑡 /𝑅 𝑐𝑡 0 ) and normalized current (𝑖 = 𝐼/2𝐼 0 ), regardless of the specific values of α and I0. These expressions were generalized for multi-step reactions, and it was shown that at either very low or very high current densities, or when I0 is the same for all reaction steps, a multi-step reaction behaves analogously to a one-step reaction. However, when I0 is different between the reaction steps, complex behaviors can arise as the resistance for each step decreases with a different current dependency. Differential resistance measurements were shown to be best suited for investigating multi-step reactions due to the more rapid decrease of 𝑅 𝑐𝑡 ′ than Rct with increasing current.