Don’t ask the Congressional Budget Office (CBO) how much interest a new spending proposal will add to the current annual budget deficit of $1.7 trillion or to the $40 trillion national debt, both of which are steadily growing as Congress and President Donald Trump continue piling on more new expenditures.

It’s not a question of whether anybody at CBO knows how to calculate what a proposed new spending measure would add in interest piled onto the deficit and the national debt. There’s a wealth of talent working in CBO who could produce that estimate in a flash. The problem appears to be that most members of Congress in both political parties don’t want to know the answer. They prefer “Washington Math.”

That’s why Rep. Michael Cloud (R-Texas) and a bipartisan group of 20 cosponsors are backing the Cost Estimates Improvement Act (H.R. 991), which requires that all future proposed spending bills “shall include, to the extent practicable, the costs (if any) of servicing the public debt” that results from a measure becoming the law of the land.

Among the co-sponsors are Democratic Representatives Ed Case of Hawaii, Jared Golden of Colorado, and Marie Gluesenkamp Perez of Washington state, joined by 17 House Republicans. Notably not among the latter group is House Budget Committee Chairman Jodey Arrington (R-Texas).

“The American people deserve a government that operates with more transparency, not less,” Cloud said in a February 2025 statement on his proposal. “Interest payments on our national debt have now surpassed $1 trillion for the first time — outpacing even our entire defense budget. This staggering reality is a direct consequence of Washington’s reckless spending. Yet, Congress routinely passes legislation without accounting for the full cost, misleading taxpayers about the financial burden being placed on future generations.”

He continued, “That’s why I introduced the Cost Estimates Improvement Act — to require the Congressional Budget Office to include debt-servicing costs in its estimates, ensuring lawmakers and taxpayers alike have a full picture of the long-term impact of Washington’s spending habits. If we don’t get serious about fiscal responsibility now, the consequences will only grow more severe.”

As Gluesenkamp Perez said in the same statement, “Servicing costs for our national debt make up one of the largest parts of our worsening deficit. Nevertheless, estimates of these costs aren’t included in the budget analysis of each piece of legislation considered by Congress.” 

“As lawmakers assess a bill’s long-term impact on our national debt, it’s important we’re seeing the full picture. Our bipartisan legislation will ensure debt servicing effects are included in the cost estimates of individual bills — that way Congress can plan for our future and avoid passing on more debt to our children,” she added.

The key problem with CBO’s failure to include projected interest expenses in its cost estimates for legislative proposals is that it presents a seriously incomplete picture, according to Joseph R. McCormack and Michael Schultz of the Fiscal Lab on Capitol Hill (FLCH). McCormack is a senior economics fellow, and Schultz is project manager for the FLCH.

The FLCH opened its doors earlier this year as “an independent research center created to provide Congress with rigorous, transparent budget and regulatory analyses aimed at addressing America’s worsening fiscal outlook.” Among the group’s founders is former Bureau of Labor Statistics (BLS) Director William Beach. Beach also served as senior economist on the Senate Budget Committee and was founder of the Heritage Foundation’s Center for Data Analysis.

“Too often, a bill is only examined based on its conventional cost, generally over a 10-year budget window. That estimate, while valuable, is not a complete measure of what legislation may cost taxpayers. Today, interest expense exceeds defense discretionary spending and is roughly equal to all nondefense discretionary spending. This cost is not financing new programs, expanding childhood education, or improving our nation’s infrastructure. It is the cost of past promises that were never fully paid for and a burden we are paying today and will likely pass down to future generations,” McCormack and Schultz write in an analysis entitled “Washington Math and the True Cost of Federal Spending,” published August 20.

As an illustration, McCormack and Schultz cite the Medicare Access and CHIP Reauthorization Act of 2015 (MACRA), which repealed Medicare’s sustainable growth rate formula for physician payments. That measure was signed into law by then-President Barack Obama.

In its official cost estimate for that bill, CBO projected it would result in an increase of $145 billion in spending and increase federal revenues by about $4 billion in the decade between 2015 and 2025. “This is the figure that dictated the debate, and yet it omitted interest expense. But because the deficits were financed and each year’s borrowing remained outstanding, interest expense constituted a significant increase in the total cost of the bill. … [A]pplying the average rate Treasury actually paid on its marketable securities in each of those years adds approximately $19 billion, bringing the total cost to roughly $160 billion, or a 13 percent increase above CBO’s score,” according to McCormack and Schultz.

And the authors add this warning: “While that bill illustrates how past spending can prove more costly than expected, the problem is not in our rearview mirror. CBO projects a $1.9 trillion deficit in fiscal year 2026, which, at an average interest rate of 3.5 percent, would generate roughly $66.5 billion in additional interest expense in 2027 alone. That cost would continue in subsequent years as the debt is rolled over.”

The Cloud proposal also drew plaudits from Maya MacGuinness, president of the Committee for a Responsible Federal Budget. “We applaud Rep. Michael Cloud’s initiative in introducing the Cost Estimates Improvement Act, which would factor interest costs in the budget estimates for legislation,” she shared. “Not considering interest on the debt in the official scores of legislation misses a real and important cost, particularly when offsets would be implemented down the road. This bill would add a missing piece to help the American public and future generations get a full accounting of what legislation costs.”

The lack of action on the Cloud proposal in the 119th Congress contrasts with how the bill was received in the 118th Congress. In the prior Congress, the House Budget Committee approved the proposal on a bipartisan basis. A spokesman for Arrington, who has been chairman of the budget panel since January 2023, could not be reached for comment on the lack of action on the Cloud bill in 2026.

One thing is certain: As long as Congress sticks to “Washington Math,” the annual federal budget deficit and the national debt that just reached $40 trillion will keep right on expanding.