The International Monetary Fund is revising its metrics on how fast governments should cut their budgets, with the IMF’s top economist making the case that Europe’s fiscal diets were too severe.

In a new paper published Thursday, IMF Economic Counsellor Olivier Blanchard and research-department economist Daniel Leigh show the IMF recommended slashing budgets too fast early in the euro crisis, starving many economies of much-needed growth.

In “Growth Forecast Errors and Fiscal Multipliers,” Messrs. Blanchard and Leigh calculate IMF and European economists underestimated the euro-for-euro effect of cutting government budgets. While economists expected that cutting a euro from the budget would cost around 50 cents in lost growth, the actual impact was more like 1.50 per euro.