A simple equation to calculate the oxidation states (oxidation numbers) of individual atoms in molecules and ions may be introduced instead of rules associated with words alone. The equation includes two of three categories of bonds, classified as proposed by Goodstein: number of bonds with more electronegative atoms and number of bonds with less electronegative atoms. Formal charge of a given atom is also taken into account in agreement with IUPAC recommendations. The equation provides a new (not described to date) way to work with the commonly used rules of oxidation state calculation, and presents an interesting opportunity for studying the redox reaction.