Half a percentage point looks small on a bond quote, but across ten years of federal borrowing it adds up to $1.9 trillion. That is what the Congressional Budget Office says deficits would grow through 2036 if every interest rate ran half a point above its forecast.
The estimate comes from a CBO report titled Projections of Deficits and Debt Under Two Scenarios With Higher Interest Rates, published October 8. CBO describes the milder scenario in basis points, “one-hundredth of 1 percentage point,” so its 50 basis points is exactly half a point on every rate across 2026 to 2036. The more severe scenario adds 150 basis points and produces a $6.0 trillion increase.
The scenarios are not predictions, and they are not aimed at any one group of readers. They matter to anyone who holds Treasury bonds, a bond fund or a retirement account heavy in fixed income, and to anyone who relies on programs whose funding competes with the interest bill, because the report shows how quickly small moves in rates change the size of that bill.
The 10-year Treasury yield closed at 5.2 percent on October 1, the first day of fiscal 2027, which is already above the 4.8 percent average that CBO’s half-point scenario assumes.
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Two scenarios, side by side
CBO’s baseline, built on its February 2026 forecast, has the 10-year Treasury rate averaging 4.3 percent over 2026 to 2036. The two alternatives are built on the higher-rate scenario in the agency’s April 2026 report on how changes in economic conditions might affect the federal budget.
In the first scenario, all rates are 150 basis points above baseline and the 10-year averages 5.8 percent. Cumulative deficits grow by $6.0 trillion, net interest costs grow by $4.9 trillion and debt-service costs grow by $1.1 trillion. Debt held by the public reaches 133.1 percent of gross domestic product in 2036, which is 12.9 percentage points above baseline.
In the second scenario, all rates are 50 basis points higher and the 10-year averages 4.8 percent. Cumulative deficits grow by $1.9 trillion, net interest costs by $1.6 trillion and debt-service costs by $297 billion. Debt held by the public reaches 124.4 percent of GDP in 2036, or 4.2 percentage points above baseline. The baseline itself has that debt at 100.6 percent of GDP in 2026 and 120.2 percent in 2036.
Where the extra $1.9 trillion comes from
Most of the increase comes from the debt the government already has. CBO says about five-sixths of the rise in the cumulative deficit comes from higher rates on baseline debt, because bonds that mature must be replaced at the new, higher rates. The remaining sixth comes from debt-service costs, meaning the interest on the additional borrowing that the higher interest bill itself requires.
Spelling it out in the milder case: $1.6 trillion of extra net interest on the debt that was already expected, plus $297 billion of interest on the extra borrowing, adds up to roughly the $1.9 trillion that CBO reports.
A yield already above the scenario
The report notes that the 10-year Treasury rate closed at 5.2 percent on October 1, 2026. That is higher than both the baseline average of 4.3 percent and the 4.8 percent average of the half-point scenario. It is also below the 5.8 percent average in the severe scenario, though a single day’s close is not an average.
The comparison should be read carefully. The scenarios describe averages across eleven fiscal years, and a daily yield can move above or below the average without settling it. Even so, the report shows why Treasury yields get attention in budget analysis: the level of rates today is already running above the path the baseline assumed.
What the estimates leave out
CBO holds every other economic variable constant, so the scenarios do not include effects such as changes in economic output. The agency says plainly that “any factors that cause interest rates to rise will have additional budgetary effects beyond those considered here.” Any change in growth, prices or tax receipts that accompanied higher rates would move revenue and spending in ways the $1.9 trillion does not capture.
The starting point for the interest bill is already large. In fiscal 2026 the government paid $1,143 billion in net interest, up $115 billion, or 11 percent, from $1,028 billion a year earlier, as CBO’s monthly budget review shows. That review also names the same two forces at work: a larger debt and higher long-term rates.
Comparing the two rate scenarios
The free source is CBO’s report page linked above, which carries the summary, the table comparing the two scenarios and the explanation of method. The numbers to compare are the cumulative increases in deficits ($1.9 trillion and $6.0 trillion), the 2036 debt-to-GDP ratios (124.4 percent and 133.1 percent) and the baseline ratio of 120.2 percent.
When a news report cites a larger or smaller figure for a rate change, the first question is which scenario it describes and over which years, because the 50-basis-point and 150-basis-point results differ by a factor of about three. The second is whether the report adds economic effects, which CBO’s does not.
The cleanest summary of the milder case is CBO’s own: all rates 50 basis points above the baseline from 2026 through 2036 adds $1.9 trillion to cumulative deficits.
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This article was produced with AI assistance and reviewed by The Financial Wire’s editorial team.
Warren Cohen is a finance writer based in Phoenix, Arizona, covering personal finance topics including credit, banking, and beginner investing. He earned his degree in business administration from Arizona State University and began his career working in consumer finance, where he gained direct experience with lending and credit systems. He now writes for personal finance websites and fintech platforms, focusing on clear, practical content that helps readers make informed financial decisions.
