NCPA Senior Fellow Steve Entin and William McBride have simulated Mitt Romney’s economic plan for the Tax Foundation:

The Romney plan would raise actual and potential GDP by about 7.4 percent over a five to ten year adjustment period. The private business sector would grow about 7.8 percent. About two-thirds of the growth in GDP would go to labor income, across the board, in the form of more hours worked and higher wages per hour. Total labor compensation in the private business sector would rise by 7.8 percent in line with GDP. About a third of the gain, pre-tax, would accrue to savers and investors. The plan would boost the capital stock by about 18.6 percent (over $5 trillion in additional investment), which is what drives the increase in productivity, wages, and hiring.

Here are the supply side responses:

We find that fully 60 percent of the static revenue loss from Romney’s plan is recovered when the dynamic effects of economic growth are taken into account. We find that while the cuts in the individual income tax rates do not “pay for themselves,” they do grow the economy 1.8 percent over the long run. The biggest boost to the economy comes from the 10 point cut in the corporate rate, which grows GDP by 2.3 percent, the capital stock by 6.3 percent, and the wage rate by 1.9 percent. The corporate rate cut is so economically beneficial that it does pay for itself, when all federal revenue effects are considered. So does the elimination of taxes on capital gains and dividends for middle-income earners and the estate tax.

John Cochrane on the study:

I actually think the model is being conservative. It seems the model is removing labor and capital distortions, but assumes no effect of tax rates on growth; the rate of technical change is given. I suspect that lowering marginal tax rates also makes people work harder at inventions. If that’s right, then there is a “growth effect” not just a “level effect.” Yes, we don’t know much about how large it is. But I submit that we know the sign!