Writing in The Wall Street Journal, Jesse Drucker notes($) that the full cost of the recently-passed economic stimulus package is slightly underestimated by the Joint Committee on Taxation's score: A round of business tax cuts in Congress's economic-stimulus package passed Thursday will cost nearly triple the official government estimate, tax experts said. The tax breaks in the package will cost more than $22 billion over the next 11 years, or roughly $15 billion more than the government's long-term estimate of $7.5 billion. To put that additional $1.4 billion cost a year into context, it is the same as the annual budget of the federal National Institute of Mental Health. ... ...the U.S. Treasury must borrow to make up for the lost revenue. These interest costs over the next decade will triple the estimated long-term cost of the proposed business tax cuts, according to an analysis done by tax experts at the request of The Wall Street Journal. And as interest expense on the national debt is the fastest growing component of the federal budget, prominent mention of interest expenses in spending and taxation debates would portray a much clearer picture of the nation's finances. So, we've put together a proposal that would impose a statutory requirement on the Joint Committee on Taxation to include interest expenses in its scorings, with the belief that budgetary decision making would be much improved when legislators have ready access to information on the interest expense of any budgetary legislation.