President Trump’s decision to move his official state of residence from high-tax New York to no (income) –tax Florida has brought public attention to an issue that has long troubled scholars, as well as designers and administrators of income tax systems: how the interaction of tax rules deferring the taxation of income and tax rules based on residency allows taxpayers to reduce and even avoid taxation of their deferred income. These discontinuities in tax treatment may lead to excessive migration, as well as reductions in state income tax revenues.

Although trans-national moves of this sort are increasingly treated as “realization events” for tax purposes, triggering the immediate taxation of accrued but untaxed gains in the taxpayer’s country of original residence, the states of the United States have not tried to impose similar rules on residents moving to other states. This reluctance may stem in part from concerns that any attempt to do so would be struck down as a violation of the federal constitution’s Commerce Clause or its Right to Travel. But it may also stem from the fact that such a forced realization rule creates a different discontinuity; a tax rule accelerating the taxation of accrued gain penalize interstate movers (relative to those who stay put and continue to benefit from tax deferrals), disincentivizing such moves. Instead of too much interstate migration, there may be too little, interfering with both economic efficiency and what could be a valuable feedback mechanism about the performance of state governments. The same discontinuity problem arises in the international realm, of course, but there the difference in institutional structures and political sensibilities—not to mention larger revenue concerns due to higher tax rates—has led to a different policy outcome.

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