The article presents GDP estimates for XV century Tuscany, based on the 1427 Florentine Catasto, one of the best quantitative sources for the Middle Ages. In 1427, Tuscany was in per capita GDP (in real terms) only slightly above England and Holland; this gap is much smaller than the one resulting from the previous GDP figures, produced by Paolo Malanima, when fit into the Maddison project. Our analysis highlights a fundamental institutional difference, between Florence on the one side, and England and Holland on the other: the former was characterized by high extractive rates in favor of the capital city, to the detriment of the subdued cities and, most of all, of the countryside; and by subsequent market blockades. This may explain why previous estimates, partly based on the construction wages in Florence (within the ‘privileged’ economy), probably overestimated GDP. It may also explain the exceptional artistic blossoming of XV century Florence, despite only a small lead in average GDP. Our work thus helps to shed new light on the history of Renaissance Italy, put into a broader comparative context.