Debt taxes during crises, a blessing in disguise?

Models with an occasionally binding credit constraint are used to study financial crises. We examine the welfare effects of implementing a policy designed for a specific type of constraint when the economy is facing a different one. To this purpose we analyze the implementation of ex ante (macroprudential) versus ex post debt taxes across four possible constraint scenarios (depending on whether creditors assess current or future and total or disposable income of debtors). Our main conclusion is that a debt tax applied only during potentially constrained periods (ex post) is a better policy in three of the four possible cases.