Heterogeneous electron transfer rate constants of a series of chemical systems are estimated using Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS), and critically compared to one another. Using aqueous, quasi-reversible redox systems, and carbon screen-printed electrodes, this work has been able to quantify rate constants using both techniques and have proved that the two methods sometimes result in measured rate constants that differ by as much as one order of magnitude. The method has been converted to estimate k(0) values for irreversible electrochemical systems such as ascorbic acid and norepinephrine, yielding reasonable values for the electron transfer of their respective oxidation reactions. Such electrochemically irreversible cases are compared to data obtained via digital simulations. The work is limited to finite concentration ranges of electroactive species undergoing simple electron processes ('E' type reactions). The manuscript provides the field with a simple and effective way estimating electron transfer rate constants for irreversible electrochemical systems without using digital software packages, something which is not possible using either Nicholson or Laviron methods. Crown Copyright (C) 2018 Published by Elsevier Ltd.