quote: Up to" is the critical modifier. The federal incentive is usually referred to as a flat $7,500 credit, but it's only worth $7,500 to someone whose tax bill at the end of the year is $7,500 or more. If the buyer of a Volt, a Nissan Leaf or any of the other eligible vehicles owes, for example, only $5,000 in income tax for a particular year, that's all the tax credit will be. Uncle Sam's not writing a refund check for the other $2,500. And an unused portion of the credit can't be applied against the following year's taxes.