State Individual Income Tax Conformity in Practice: Evidence From the Tax Cuts & Jobs Act

Monahan, Amy B.

Nearly every state incorporates the federal tax code into its individual income tax system. This widespread incorporation has many supporters and has been justified on the basis that it is necessary in order for states to have a simple and efficient tax system. This article explores the practical effects and dynamics of state tax conformity through a novel examination of how states that tightly conformed to the federal individual income tax responded to the recently enacted Tax Cuts and Jobs Act which, for these states, would have both raised state taxes and changed the distribution of state tax burdens. The study reinforces concerns raised in both the theoretical and economic literature regarding conformity’s enhancement of revenue volatility and likelihood of distorting state legislative decision-making, while adding several new observations of conformity’s impact. The study illustrates that conformity imposes significant time constraints on state legislatures, conformity causes not only revenue shocks, but tax policy shocks, and even where state revenue is kept constant following a federal change, conformity may cause relative state tax burdens to change. Based on these findings, the article concludes by offering suggestions for how states can move past the idea that extensive conformity with the federal tax code is required and instead design an individual income tax system that is simple, efficient, and enhances a citizen’s relationship to the state.

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Columbia Journal of Tax Law

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July 22, 2020