The past two years Kansas reduced its state income tax rates. As a result, the top rate of income tax faced by Kansas residents (combined state and federal) rose from 41.45% in 2012 to 48.3% in 2013 and then fell a tad to 48.2% in 2014 (if they don’t itemize.) That’s a pretty tiny drop in the top marginal tax rate in 2014, and a much bigger rise in 2013.
I consider myself a moderate supply-sider, but I certainly wouldn’t expect such a tiny tax cut to significantly affect behavior. And any effects that did occur would happen very gradually, over a period of many years. For instance, firms might be slightly more likely to move to Kansas. But even after the tax cut, the top rate is almost as high as in Massachusetts, so Kansas is certainly not a tax haven like Washington or Texas, which have no state income tax.
I can’t imagine any serious economist predicting that the Kansas rate cut would boost Kansas GDP by 25% or more. Why did I pick that figure? Because the Kansas state income tax top rate fell from 6.45% in 2012 to 4.8% in 2014, which is roughly a 25% rate cut. In order for that rate cut to boost Kansas tax revenues, you’d have to see Kansas GDP rise by more than 25%. That’s obviously absurd.
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