what % of a national sales tax would have to be to replace the income tax.
It depends upon what all gets covered. It could be as low as 10% if everything were covered including the sale of labor (i.e. an earned wages tax.) Once you start exempting whole categories of the GDP from being taxed, the rate on what remains would need to be increased. Assuming a sales tax on just the items traditionally covered by such a tax, you're getting up into the 30% range. (Assuming the percentage is reported as it traditionially is, as an addition to the quoted price. If you do it as the proponets of the self-described Fair Tax do, as a percentage of the total amount paid by the buyer for the good or service, then you get numbers in the 23% range.) The biggest problem with switching to a national sales tax instead of an national income tax, is that if it is done quickly, the shock to our economy would probably be devastating while agradual change that gave people time to adjust to the new system would likely get stuck midway, leaving us with both taxes.