Under traditional formulations, lower capital income tax rates reduce the user cost of capital and stimulate investment. The traditional approach, however, implicitly or explicitly considers a revenue-neutral reduction in capital income taxation. We extend the traditional approach by considering a reduction in taxes that generates an increase in the budget deficit; the expanded budget deficit may raise interest rates and the opportunity cost of investment. This provides a mechanism through which tax cuts can raise the cost of capital. Representative calculations show that making the administration's recent tax cuts permanent would be to raise the user cost of capital.