This paper establishes, and illustrates for the case of the UK, a temporal method for calculating the labour values of outputs from any process or sector of a market economy. It exhibits the temporal calculation of the Monetary Equivalent of Labour Time (MELT), the general ratio between monetary and labour time magnitudes, for a single national economy, but does not correct for the consequences of value transfers within the world economy as a whole. The method is nevertheless generalisable, provided international value transfers are properly accounted. If coupled with a proper treatment of production and unproductive labour, it thus sets the value-theoretic reconstruction of the National Accounts on a completely rigorous foundation, by making it possible to transform all the categories and measures of the SNA method into the Marx’s categories and measures.