Abstract Measures of potential output and the output gap are increasingly being developed and used to concisely quantify and monitor the risk of price accelerations stemming from rises in aggregate demand that are not met by a corresponding increase in supply. They often play a prominent role in the price determination mechanisms of macroeconometric models. In this paper we build a measure of potential private-sector value added for the Italian economy that is consistent with the capital accumulation process in the Banca d'Italia's Quarterly Model — and more generally with the rest of the supply-side block of that model. More specifically, we exploit the fact that the investment function can be thought of as a relationship transforming desired gross additions to capacity output into capital accumulation by means of a conversion factor (the optimal capital/output ratio). Thus, if one removes the component of investment decisions that stems from changes in the relative price of the production factors, (i.e. in the optimal capital/output ratio), then a measure of the desired gross addition to capacity may be constructed. The results draw a cyclical picture of the degree of capacity utilisation for the period 1970–1997 that is roughly in line with those produced by the Wharton and Hodrick–Prescott filter approaches, as well as with the pictures resulting from the ISAE, IMF, European Commission and OECD measures of the output gap. Our investment-function-based measure appears to be a promising indicator of the pressure exerted on prices by demand accelerations. Its empirical properties are, on the whole, acceptable and plausible.