We present a method for analysing propagation errors in membrane capacitance (C(m)) measurements under the whole-cell patch-clamp configuration, which mainly focusses on errors in C(m) estimates due to the 'residual' fast capacitance (DeltaC(p)). The method employs a quasi-phasor diagram for visualisation of the analysis. Our results show that both under- and over-compensation of fast capacitance will cause errors in C(m), and errors in the magnitude and in the phase angle of cell admittance make their respective and opposite contributions to propagation errors in C(m). Within optimal frequencies, over-compensation of fast capacitance will cause a smaller propagation error in C(m) and produce more accurate C(m) estimates than under-compensation of fast capacitance will do. Information about how other cell parameters, such as smaller series resistance, baseline C(m) value and the stimulus frequency, change the total error in C(m) due to DeltaC(p) is also provided. Guidelines for accurate C(m) recordings are given to make it easy for users to perform their own error analysis.