The paper introduces the notion of different methods of calculating and analysing profitability as signatures of capitalism at different stages of development. Interactions between the development of the productive forces and the socialisation of capital ownership jointly impact on these signatures, such that profit calculations are historically contingent. These interactions take the identification of capitalism beyond simple associations with the presence or absence of double-entry bookkeeping (DEB), the capital account or return on capital calculations. Profit calculations are implicated in the process of transition from feudalism to capitalism by enabling the private enforcement of profit levels in excess of legally regulated interest rates or through fairly remunerated labour. The modern usage of ROCE is linked to the development of the productive forces and the socialisation of capital ownership.