New York’s mayor-elect, Zohran Mamdani, campaigned on a promise to raise the city’s income tax on its richest residents from 3.9% to 5.9%. Combined with the state income tax, which is 10.9% for the top bracket, the increase would cement the city’s position as having the highest taxes on top earners in the country.

It set off a chorus of warnings about the tax flight of the city’s wealthiest residents.

Hedge fund billionaire Bill Ackman claimed that both the city’s businesses and wealthy residents “have already started making arrangements for the exits.”

New York Gov. Kathy Hochul echoed the concern, opposing the proposal “because we cannot have them leave the state.” Before the election, Mamdani’s opponent, former New York governor Andrew Cuomo, joked that if Mamdani won, “even I will move to Florida.”

I research whether high earners actually move when their taxes go up. My colleagues and I have analyzed millionaire taxes in New Jersey and California, the migration of Forbes billionaires globally and decades of IRS data tracing where Americans with million-dollar incomes live.

Top earners are often thought of as “mobile millionaires” who are ever searching for lower-tax places to live. In reality, they’re often reluctant to leave the places where they built their careers and raised their families.

At the same time, there are grains of truth in the tax migration arguments, so it’s important to carefully parse the evidence.

The first fact is simple: Millionaires have low migration rates.

Mobility in America is highest among people who........

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