The Accuracy of CBO’s Budget Projections for Fiscal Year 2024

After each fiscal year ends, the Congressional Budget Office reviews its projections of federal revenues and outlays and the government’s budget deficit and compares them with actual budgetary outcomes for that year. By identifying the factors that might have led to under- or overestimates of particular categories of federal revenues and outlays, CBO seeks to improve the accuracy of its work.

The agency’s baseline projections do not include forecasts of future changes in law. Therefore, to compare those projections with actual outcomes, CBO adjusted them to include the estimated effects of legislation enacted after the projections were developed.1

For several reasons discussed later in the report, this analysis mainly compares CBO’s May 2023 budget projections with actual outcomes for 2024. But actual outcomes can also be usefully compared with the agency’s most recent budget projections, published this past June. After adjusting those June 2024 projections, CBO found that it overestimated the 2024 deficit by $84 billion (see Box 1). That overestimate occurred mostly because CBO’s June projections included estimated budgetary effects of the Administration’s proposed rule to reduce many borrowers’ balances on student loans, but the Administration did not record any costs related to the rule in 2024.

The overall differences between CBO’s updated May 2023 baseline projections and actual outcomes in 2024 were as follows (see Table 1):

• Deficit. CBO underestimated the 2024 deficit, which totaled $1.8 trillion, by $306 billion. That underestimate equals 1.1 percent of gross domestic product (GDP), which is the size of the average absolute error in the agency’s deficit projections for 1985 to 2023.
• Revenues. CBO’s projection of $4.8 trillion for federal revenues in 2024 was too low—by $72 billion, or 1 percent. That difference was much smaller than the average absolute error of about 6 percent in CBO’s revenue projections for 1983 to 2023.
• Mandatory outlays. CBO’s projection of $3.8 trillion for mandatory outlays in 2024 was too low—by $252 billion, or 6 percent. That difference was about twice the average absolute error of 3 percent in projections of mandatory outlays for 1993 to 2023. The largest factor was an underestimate of outlays for higher education loans and programs, primarily stemming from the Administration’s revision of its estimates of the costs of previously issued student loans.
• Discretionary outlays. CBO’s projection of $1.8 trillion for discretionary outlays in 2024 was too high—by $11 billion, or 1 percent. That difference was smaller than the average absolute error of about 2 percent in CBO’s projections of discretionary outlays for 1993 to 2023.
• Net outlays for interest. CBO’s projection of $0.7 trillion for net interest outlays in 2024 was too low—by $137 billion, or 16 percent. That difference was larger than the average absolute error of about 11 percent in CBO’s projections of such outlays for 1993 to 2023, and it occurred mainly because CBO’s forecast of interest rates was too low.

How CBO Conducted This Analysis

CBO regularly publishes baseline projections of federal revenues, outlays, and deficits for the current fiscal year and the ensuing decade. Those projections reflect the assumption that current laws governing taxes and spending will generally remain unchanged. This analysis focuses on the May 2023 baseline budget projections because CBO estimated the effects of proposed legislation affecting the 2024 budget year and beyond in relation to that spring baseline.2 Moreover, the agency typically uses the technical assessments (of, for example, how quickly appropriations would be spent) and economic projections underlying its spring baseline from the previous fiscal year to prepare cost estimates for legislation affecting the budget year and beyond.3 (The budget year is the second year of the period covered by CBO’s baseline projections; it usually begins several months after updates to the baseline projections are released in the spring.)

Additionally, the staff of the Joint Committee on Taxation (JCT) typically use the revenue projections completed for the winter baseline in January or February of the previous fiscal year (in this case, February 2023) to estimate the effects of legislation affecting the budget year and beyond. Those revenue projections rely on the same economic forecast that underlies the spring baseline and are typically very similar to the revenue projections in that spring baseline.

Any comparison of CBO’s projections with actual outcomes is complicated by the effects of legislation enacted after the projections were completed. When it prepares its baseline budget projections, CBO does not attempt to predict future legislative changes or their effects on revenues and outlays; yet those changes invariably cause budgetary outcomes to differ from the agency’s estimates.

To account for those changes, CBO updated its projections to incorporate the estimates of the budgetary effects of subsequent legislation that were reported by CBO and JCT, as well as the estimated increase in spending for interest on the federal debt that resulted from enacted legislation. Those effects on interest are not included in CBO’s cost estimates. Thus, any errors in the initial cost estimates are reflected in the projection errors discussed in this report.

Adjusting projections to reflect the cost estimates for enacted legislation that CBO provided to the Congress for budget enforcement purposes allows the agency to evaluate the quality of that information. The Congress generally uses adjusted baseline projections when enforcing budgetary rules as legislation is enacted throughout the year. But the effects of legislation may differ from the adjustments CBO made to add them to the projections. For that reason, this report examines the accuracy not only of CBO’s initial baseline projections but also of the information about the budgetary effects of legislation, including appropriations for 2024, that CBO provided to the Congress from May 2023 through September 2024 (the end of fiscal year 2024).

How CBO’s May 2023 Projections for 2024 Compare With Actual Outcomes

In its updated May 2023 baseline projections, which include the estimated budgetary effects of subsequent legislation, CBO underestimated revenues by 1 percent and outlays by 6 percent for 2024. Because the underestimate of outlays was larger than the underestimate of revenues, the agency underestimated the federal deficit for that year.

Revenues

CBO’s projection of revenues for 2024 was $4.8 trillion, $0.1 trillion less than the actual amount (see Table 2). That underestimate reflects offsetting errors among various revenue sources: CBO underestimated receipts from payroll taxes and corporate income taxes but overestimated receipts from individual income taxes and customs duties.

Projections of tax revenues are sensitive to underlying economic conditions and to how policies are implemented and how taxpayers respond to them. Revenues typically increase or decrease as economic activity increases or decreases, and rising prices tend to boost revenues. Moreover, when policies are implemented, the Treasury and the Internal Revenue Service (IRS) can take actions that result in payments’ being deferred beyond their normal or originally scheduled deadlines. For example, those agencies sometimes take more time than is typical to issue regulations and guidance for new provisions, especially for those that are particularly complex. Additionally, under some circumstances, the IRS is required to postpone certain deadlines, as it did in 2023 when it delayed tax payment deadlines for most taxpayers in California because much of the state was declared a federal disaster area. Revenues are also affected by how taxpayers respond to policy changes, which may differ from CBO’s and JCT’s expectations.

Differences between the actual implementation and use of new and existing tax policies and CBO’s and JCT’s assessments about how soon new tax policies would take full effect and how people would respond to them probably contributed to the overall error in CBO’s revenue projections. Differences between actual economic conditions and CBO’s economic forecast also contributed to errors in the agency’s projections of revenues from some sources, but such differences may have reduced errors in its projections of revenues from other sources. The specific factors contributing to the misestimates of revenues will be better understood as more detailed tax data become available over the next two years.

Individual Income Taxes. CBO’s projection of receipts from individual income taxes in 2024 was $2.5 trillion, $48 billion (or 2 percent) more than the $2.4 trillion that was actually collected. In CBO’s assessment, the largest factors contributing to that overestimate were an overestimate of the amount of realized capital gains and the Treasury’s reclassifying certain income tax receipts as payroll tax receipts. Those factors were partly offset by the IRS’s postponing tax payment deadlines and by income growth that was stronger than anticipated.

Lower-than-anticipated receipts from taxes on capital gains were probably the largest contributor to the overestimate of receipts from individual income taxes. In May 2023, CBO projected that realizations of capital gains would decline sharply from their historical high of $2.0 trillion in calendar year 2021 to $1.5 trillion in calendar year 2023. However, on the basis of preliminary tax data for calendar year 2023, CBO now estimates that those realizations declined even more sharply than anticipated and totaled about $1.0 trillion. That difference suggests that CBO overestimated tax liabilities by more than $0.1 trillion.

A reduction in individual income tax receipts because of a reallocation by the Treasury also contributed to the overestimate. In 2024, the Treasury reclassified $40 billion of past individual income tax receipts as payroll tax receipts, thus reducing the amount of income taxes recorded for the year. When the Treasury receives payments of withheld taxes, it cannot distinguish payroll taxes from individual income taxes. Instead, it first allocates withheld taxes to one category or the other on the basis of estimates made in advance of the actual collections. As additional information (including details from tax returns) becomes available, the Treasury periodically revises those allocations.

Another possible factor is that the distribution of earnings may have differed from the distribution that CBO projected. For example, a larger proportion of earnings than CBO projected may have accrued to workers below the top 10 percent of the distribution. If so, earnings would have been taxed at a lower rate than the agency expected.

One factor that boosted individual income tax receipts compared with projected amounts was the IRS’s postponing payment deadlines for taxpayers affected by natural disasters. Payments that would typically have been due throughout fiscal year 2023 were postponed until fiscal year 2024. Most significantly, the payment deadline for most taxpayers in California was extended to November 2023. CBO estimates that the postponements shifted about $35 billion in receipts from 2023 into 2024.

Growth in income was also stronger than CBO projected in May 2023. For 2024, the Bureau of Economic Analysis’s (BEA’s) current estimate of income from sources subject to tax—including wages and salaries, distributions from pensions and retirement accounts, and income from rental property, interest, and dividends—is 2 percent higher than CBO projected in May 2023.

Payroll Taxes. CBO’s projection of receipts from payroll taxes in 2024 was $1.6 trillion, $76 billion (or 4.4 percent) less than the actual amount of $1.7 trillion. Most of that underestimate resulted from the Treasury’s reclassifying past individual income tax receipts as payroll taxes (as discussed above), boosting the latter by $40 billion in 2024.

Faster-than-expected growth in wages—the largest component of the tax base for payroll taxes—also contributed to CBO’s underestimate of payroll tax receipts. In September 2024, BEA published revised estimates of nominal wages and salaries, which indicated growth was about 1 percent faster than CBO anticipated in May 2023.

Corporate Income Taxes. CBO’s projection of receipts from corporate income taxes in 2024 was $478 billion, about $52 billion (or 10 percent) less than the $530 billion actually collected. That underestimate is partly attributable to administrative actions that granted deferrals of regular payments and established a longer timeline than CBO and JCT anticipated for enforcing new tax provisions. For example, for taxpayers affected by natural disasters, including most taxpayers in California, the IRS postponed the filing deadlines for payments usually due throughout the year. CBO estimates that about $35 billion in corporate income tax payments was deferred from 2023 into 2024.

Stronger-than-anticipated growth in profits also contributed to CBO’s underestimate of receipts from corporate income taxes. The agency projected that nominal domestic corporate profits would decline in both calendar years 2023 and 2024. But BEA estimates that those profits grew by 6 percent in calendar year 2023 and at a similar rate in the first half of calendar year 2024.

Other Receipts. CBO’s projection of revenues from all other sources in 2024 was $261 billion, $8 billion (or 3 percent) more than the actual amount. That difference reflects offsetting errors among sources: Customs duties were lower than projected, but revenues from estate and gift taxes and from miscellaneous fees and fines were higher than projected.

CBO’s projection of customs duties was $20 billion (or 26 percent) more than the actual amount collected in 2024. Duties from imports subject to higher administratively imposed tariffs—particularly imports from China—fell more rapidly than anticipated.

CBO underestimated collections of estate and gift taxes by $7 billion (or 22 percent) and collections of fees and fines by $5 billion (or 12 percent); those underestimates partially offset the overestimate of customs duties.

Outlays

Updated to include the estimated effects of subsequently enacted legislation, CBO’s May 2023 baseline projection of outlays in 2024 was $6.4 trillion, $378 billion (or 6 percent) less than the actual amount. In its baseline projections, CBO divides federal outlays into three broad categories: mandatory, discretionary, and net outlays for interest.4 CBO underestimated mandatory outlays and net outlays for interest, and it slightly overestimated discretionary outlays.5

Mandatory Outlays. CBO’s projection of mandatory outlays in 2024 was $3.8 trillion, $252 billion (or 6 percent) less than the actual amount of $4.1 trillion (see Table 3). Underestimates for higher education loans and programs, Medicaid and the Children’s Health Insurance Program (CHIP), and deposit insurance were the largest contributors. Administrative actions taken since CBO completed its May 2023 baseline projections boosted outlays in 2024 by roughly $55 billion, mostly for deposit insurance.

Higher Education Loans and Programs. CBO’s projection of outlays for higher education loans and programs in 2024 was $103 billion less than the actual amount. Most of that difference, $74 billion, resulted from increases that the Administration made to the estimated costs of outstanding loans issued before 2024. Typically, CBO does not include such revisions to estimated subsidy costs in its baseline projections until the Administration publishes the amounts of revisions it will record as outlays.6

Most of the remaining $29 billion of the difference was attributable to an increase in estimated subsidy costs for loans issued in 2024. (That amount represents the net present value of loan disbursements minus repayments of interest and principal. A present value summarizes a series of projected values in the future as a single value in the present.) That increase stemmed from a greater volume of consolidation loans, which allow borrowers to combine one or more outstanding loans into a new loan, and a higher average subsidy rate for loans.

Another factor contributing to the remaining $29 billion of the difference between actual and projected outlays for higher education loans and programs was the Administration’s changes to the income-driven repayment (IDR) plans that were finalized by the Department of Education in July 2023. For most borrowers, those changes made the IDR plans more generous, and many borrowers selecting an IDR plan will now pay less in principal and interest than they would have previously paid.

Medicaid and CHIP. CBO underestimated outlays for Medicaid and CHIP in 2024 by $80 billion (or 12 percent). Outlays for Medicaid were greater than expected by $77 billion even though enrollment in the program declined after the continuous eligibility policy put in place during the coronavirus pandemic ended on April 1, 2023. Spending on Medicaid did not decline at the same rate as enrollment did and remained higher than expected. The specific factors contributing to the underestimate will be better understood as more data become available. CBO underestimated outlays for CHIP because of higher-than-expected spending per beneficiary.

Deposit Insurance. CBO underestimated outlays for deposit insurance in 2024 by $44 billion. That underestimate stems from payments made by the Federal Deposit Insurance Corporation (FDIC) to resolve bank failures that occurred in spring 2023. Seven bank failures have occurred since the beginning of March 2023 (four in fiscal year 2023, two in fiscal year 2024, and one in fiscal year 2025). CBO’s May 2023 baseline projections reflected the expectation that the FDIC would make most of the payments related to resolving the bank failures in 2023. But the resolution happened more slowly, and, in 2024, the FDIC sold notes to the Federal Financing Bank in exchange for $43 billion in borrowing, financed through the issuance of Treasury securities.7 Those transactions were recorded in the federal budget as $43 billion in outlays by the FDIC in 2024, leading to the underestimate.

Medicare. CBO’s projection of Medicare outlays in 2024 was $36 billion (or 4 percent) less than actual outlays. That underestimate was mainly attributable to lower-than-expected spending in Part B for both traditional Medicare and Medicare Advantage.

Income Security Programs. CBO overestimated outlays for income security programs in 2024 by $33 billion (or 9 percent). (Those programs make payments to certain people and government entities to assist the poor, the unemployed, and others in need.) The largest differences between projected and actual amounts were in outlays associated with the Supplemental Nutrition Assistance Program (SNAP) and unemployment compensation. The agency overestimated outlays for SNAP by $20 billion and unemployment compensation by $13 billion, mainly because participation in those programs was less than anticipated.

Health Insurance Subsidies and Related Spending. CBO’s projection of outlays for subsidies for health insurance purchased through the marketplaces established by the Affordable Care Act and related spending was $19 billion (or 16 percent) less than the actual amount in 2024. That underestimate mostly resulted from higher-than-expected enrollment in subsidized health insurance coverage.

Education Stabilization Fund. In its May 2023 baseline projections, CBO underestimated outlays from the Education Stabilization Fund in 2024 by $16 billion. (That fund provided money to help K-to-12 schools, as well as colleges and universities, respond to the effects of the pandemic.) CBO expected that as the effects of the pandemic dissipated, the rate of spending from the fund would slow compared with the rate in the prior two years. But actual outlays from the fund in 2024 were slightly more than outlays in either 2022 or 2023.

Revisions to the Estimated Costs of Other Credit Programs. Federal agencies regularly update their estimates of the subsidy costs of certain federal loans and loan guarantees made in previous years. In 2024, reestimates of the subsidy costs of federal credit programs, other than the previously discussed revisions to the estimated costs of student loans, increased recorded outlays, on net, by $15 billion. The largest of those changes was a $33 billion increase in the cost of certain disaster relief loans made by the Small Business Administration. That increase was partly offset by the second-largest change, a $14 billion reduction in the cost of certain loan guarantees provided by the Federal Housing Administration.

Pension Benefit Guaranty Corporation. CBO projected that outlays of the Pension Benefit Guaranty Corporation (PBGC) would total $1 billion in 2024, but they actually amounted to $12 billion. That underestimate occurred mainly because some outlays from the PBGC’s special financial assistance program for financially troubled multiemployer pension plans were made later than CBO anticipated. In May 2023, CBO projected that $76 billion would be paid in 2023 and $8 billion would be paid in 2024; but $46 billion was paid in 2023, and $15 billion was paid in 2024.

Social Security. CBO overestimated outlays for Social Security by $2 billion (or less than 1 percent). That slight overestimate was the net result of a small overestimate of the cost-of-living adjustments that the Social Security program provides to beneficiaries, partly offset by a small underestimate of the Old-Age and Survivors Insurance caseload.

Other Mandatory Programs. In its May 2023 baseline projections, CBO overestimated outlays for all other mandatory programs by $36 billion (or 9 percent). The largest difference was in outlays for veterans’ benefits and services: CBO’s projection exceeded the actual amount by $6 billion (or 3 percent).

Discretionary Outlays. To evaluate its projections of discretionary outlays, CBO updated the funding amounts in its May 2023 baseline projections to reflect the regular full-year appropriations provided for 2024 in appropriation bills enacted in the first half of the fiscal year. The updated projections generally reflect the same technical assessments and economic projections that underlaid the agency’s May 2023 baseline projections. For supplemental appropriations, however, CBO applied technical assessments that reflected the agency’s estimates when the appropriations were enacted. With those adjustments, CBO’s projection of discretionary outlays in 2024 was $1.8 trillion, $11 billion (or 1 percent) more than the amount recorded for the year. CBO overestimated defense outlays and nondefense outlays by $3 billion (or less than 1 percent) and $8 billion (or 1 percent), respectively.

CBO’s projections of discretionary outlays for most agencies were close to the actual amounts in 2024 (see Table 4). The largest differences between projected and actual amounts were as follows:

• CBO’s projection of spending by the Department of Health and Human Services was $7 billion (or 5 percent) more than the actual amount—a difference stemming from lower-than-anticipated spending on refugee and entrant assistance programs.
• CBO underestimated spending by the Department of Homeland Security by $7 billion (or 7 percent). Higher-than-anticipated outlays for activities of the Federal Emergency Management Agency accounted for most of that difference.
• CBO’s projection of spending by the Department of Veterans Affairs exceeded the actual amount by $5 billion (or 4 percent), mainly because outlays for medical services were less than anticipated.

Net Interest. Net outlays for interest consist of the government’s interest payments on federal debt, offset by interest income that the government receives. CBO’s projection of those outlays for 2024 was $744 billion, $137 billion (or 16 percent) less than the actual amount of $881 billion (see Table 1).

Most of the difference between projected and actual net outlays for interest was attributable to economic factors. In particular, short-term interest rates in 2024 were higher than CBO forecast in December 2022, when it finalized the economic forecast underlying its May 2023 baseline budget projections. CBO projected that the interest rate on 3-month Treasury bills would average 3.6 percent in 2024, but that rate actually averaged 5.2 percent. CBO also underestimated longer-term interest rates, but that misestimate was smaller: In its February 2023 economic forecast (which was finalized in December 2022), CBO projected that the interest rate on 10-year Treasury bonds would average 3.9 percent in 2024, whereas that rate actually averaged 4.2 percent.

How the Accuracy of CBO’s May 2023 Projections for 2024 Compares With the Accuracy of Its Past Budget Projections

Measured as a percentage of GDP, the error in CBO’s deficit projection for 2024 was about the same as the historical average for the agency’s budget-year deficit projections.8 The error in CBO’s revenue projection for 2024 was smaller than the average absolute error in such projections for previous years.9 And the error in projected outlays for 2024 was larger than the historical average for budget-year outlay projections.

Deficits

The average absolute error in CBO’s budget-year deficit projections made for 1985 to 2023 equaled 1.1 percent of GDP. The agency overestimated the deficit roughly two-thirds of the time (see Figure 1). In its updated May 2023 baseline projections, CBO underestimated the deficit in 2024 by $0.3 trillion, or 1.1 percent of GDP.

Revenues

In CBO’s budget-year projections for 1983 to 2023, the average absolute error in revenue projections was 6 percent, and CBO overestimated total revenues about as often as it underestimated them. In the agency’s updated May 2023 baseline projections, revenues in 2024 were less than the actual amount recorded that year by 1 percent (see Figure 2).

CBO overestimated receipts from individual income taxes in 2024 by 2 percent—a smaller error than most of the errors in projections of such receipts for 1983 to 2023. CBO’s projection of receipts from payroll taxes was 4 percent less than the actual amount collected, about the same as most of the errors in the projections for the 1983–2023 period.

CBO’s projections of corporate income taxes have been particularly uncertain. The average absolute error in the agency’s projections of receipts from that source for 1983 to 2023 was 18 percent, the largest of the errors in the agency’s projections of the major sources of revenues. In its projection for 2024, CBO underestimated receipts from corporate income taxes by 10 percent.

The agency’s projection of receipts from all other revenue sources was about 3 percent higher than actual amounts in 2024. The typical error over the 1983–2023 period for such receipts was 6 percent.

Outlays

In CBO’s budget-year projections of outlays for 1993 to 2023, the average absolute error equaled 3 percent, and the agency overestimated total outlays about three-quarters of the time.10 In its updated May 2023 baseline projections, the agency underestimated total outlays in 2024 by 6 percent (see Figure 2).

CBO underestimated mandatory outlays in 2024 by 6 percent—a larger error than exhibited by most of its past projections of such spending. CBO’s projection of discretionary spending in 2024 was close to the actual amount—an overestimate of 1 percent.

Although CBO has often overestimated net outlays for interest, the agency underestimated such outlays in its projection for 2024 by 16 percent. That is a larger error than exhibited by most of CBO’s past projections of net outlays for interest.

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1. 1. In addition to incorporating the estimated effects of subsequently enacted legislation, the agency removed outlays for Fannie Mae and Freddie Mac from its projections and from estimates of actual outcomes because CBO and the Administration differ in the way they account for those entities’ transactions. For information about the differences, see Congressional Budget Office, Accounting for Fannie Mae and Freddie Mac in the Federal Budget (September 2018), www.cbo.gov/publication/54475.

2. 2. Congressional Budget Office, An Update to the Budget Outlook: 2023 to 2033 (May 2023), www.cbo.gov/publication/59096. For CBO’s June 2024 projections, see Congressional Budget Office, An Update to the Budget and Economic Outlook: 2024 to 2034 (June 2024), www.cbo.gov/publication/60039.

3. 3. For last year’s edition of this report, see Congressional Budget Office, The Accuracy of CBO’s Budget Projections for Fiscal Year 2023 (December 2023), www.cbo.gov/publication/59682. CBO also periodically issues comprehensive evaluations of its budget projections. See, for example, Congressional Budget Office, An Evaluation of CBO’s Projections of Deficits and Debt From 1984 to 2023 (December 2024), www.cbo.gov/publication/60664. To review the data that the agency uses to evaluate the accuracy of its projections of outlays, revenues, deficits, and debt, see Congressional Budget Office, “Evaluating CBO’s Projections of Components of the Federal Budget” (GitHub, updated December 2024), https://github.com/US-CBO/eval-projections.

4. 4. Mandatory (or direct) spending includes outlays for some federal benefit programs, such as Social Security, Medicare, and Medicaid, and certain other payments to people, businesses, nonprofit institutions, and state and local governments. It is governed by statutory criteria and is not normally controlled by the annual appropriation process. Discretionary spending is controlled by appropriation acts that specify the amount, purpose, and period of availability of funding for a broad array of government activities, such as defense, law enforcement, and transportation. Net outlays for interest consist of the government’s interest payments on debt held by the public minus interest income that the government receives.

5. 5. The Treasury does not report discretionary and mandatory totals for accounts that include both types of outlays. For those accounts, CBO estimated the amounts that the Office of Management and Budget will ultimately categorize as mandatory and discretionary for 2024.

6. 6. Under the Federal Credit Reform Act of 1990, a program’s subsidy costs are calculated by subtracting the present value of the government’s projected receipts from the present value of its projected payments. The estimated subsidy costs can be increased or decreased in subsequent years to reflect updated assessments of the payments and receipts associated with the program. (The present value depends on the rate of interest—the discount rate—that is used to translate future cash flows into current dollars.)

7. 7. CBO expects those notes to be repaid over the next several years; those transactions would be recorded in the federal budget as receipts.

8. 8. For more detailed discussions about the quality of CBO’s projections, see Congressional Budget Office, An Evaluation of CBO’s Projections of Deficits and Debt From 1984 to 2023 (December 2024), www.cbo.gov/publication/60664, An Evaluation of CBO’s Projections of Outlays From 1984 to 2021 (April 2023), www.cbo.gov/publication/58613, and An Evaluation of CBO’s Past Revenue Projections (August 2020), www.cbo.gov/publication/56499.

9. 9. The average absolute error is an average of projection errors without regard to whether they are positive or negative. For outlay and revenue projections, the projection error is the projected amount minus the actual amount, divided by the actual amount. For deficit projections, the projection error is the difference between the projected and actual amounts expressed as a percentage of GDP. CBO calculates the errors for deficit projections that way because if they were expressed as a percentage of the dollar value of the actual amount, relatively small differences between projected and actual amounts in years with small deficits or surpluses would result in large projection errors.

10. 10. The data necessary to calculate the projection errors for budget-year projections of most types of spending are available only for projections made for 1993 and beyond.