The most usual procedure to estimate the chain transfer ratio in vinyl polymerization is to use a Mayo plot. This plot can only be applied directly when the polymerization rate is not modified by the chain transfer agent. In spite of this, the equation has been applied to several systems where this condition is not fulfilled. In the present work we present a slightly modified equation that can be employed irrespective of the changes in rate. This equation is applied to several systems reported in the literature. The improvement in the interpretation of the results in these systems is discussed.