Most statistical agencies construct sectoral real GDP using double deflation and base periodprices. When the base period price used for intermediate inputs is not equal to theirmarginal revenue product, such as when firms apply a markup, real GDP fluctuations becomemechanically linked to variations in intermediate inputs. This is because these inputsgenerate profits that are incorporated into real value added. Taking this channel into account,we demonstrate that real GDP reported in national accounts substantially divergesfrom a theory-consistent "physical" value added. This, in turn, has implications for themeasurement of productivity. Between 1999 and 2021, "physical" productivity cumulativegrowth in the Finance sector was 15pp lower compared to the Solow Residual, while it was 15pp higher in the Manufacturing sector.