The Congressional Budget Office: Who Scores the Bills
Before any major bill becomes law, Congress needs to know what it costs. The CBO provides that answer — and both parties spend enormous energy tryingth:640px;margin:0 0 8px;"> Before any major bill becomes law, Congress needs to know what it costs. The CBO provides that answer — and both parties spend enormous energy trying to either cite or discredit its estimates depending on the legislation in question.
What the CBO Does and How It Works
The Congressional Budget Office was created by the Congressional Budget Act of 1974, after Congress decided it needed its own independent budget analysis to counter the executive branch's Office of Management and Budget (OMB). Before CBO, Congress largely relied on the president's own budget projections — which had obvious political incentives to be optimistic.
Cost estimates (scores): When Congress asks the CBO to score a bill, the agency estimates the bill's effect on federal revenues, spending, and the deficit over a 10-year budget window. These estimates compare spending under the proposed bill to a "baseline" — what would happen if current law remained unchanged. A bill that costs $500 billion over 10 years in new spending means federal outlays are $500 billion higher than the baseline.
Mandatory vs. discretionary spending: CBO scores mandatory spending (entitlements like Medicare, Social Security, Medicaid) with precision, since these programs spend according to formulas. Discretionary spending (annual appropriations) is harder to score because future Congresses can change appropriation levels. CBO cannot score hypothetical future appropriations it assumes will never actually be made.
Revenue scoring: For tax legislation, CBO and the Joint Committee on Taxation (JCT) estimate whether a bill increases or decreases federal revenues. Tax cuts that cost more than they raise in revenue over 10 years add to the deficit — which matters enormously for reconciliation.
The nonpartisan mission: CBO's director is appointed by congressional leaders of both parties and serves a 4-year term. The agency does not make policy recommendations — it simply reports what it estimates the numbers to be. Both parties have criticized CBO scores they disagreed with, but the agency's structural independence has generally been respected.
High-Profile CBO Scores and Their Political Impact
| Bill / Year | CBO Score | Political Impact |
|---|---|---|
| ACA (2010) | Deficit-reducing over 10 years; 32M newly insured | Score helped Democrats argue the bill was fiscally responsible; Republicans disputed methodology |
| AHCA (2017) | 23M would lose coverage over 10 years | Score significantly damaged support for ACA repeal; bill failed in Senate |
| Tax Cuts and Jobs Act (2017) | $1.5T added to deficit over 10 years | Republicans used reconciliation to pass without 60 votes; had to sunset provisions at 10 years |
| Build Back Better (2021) | Scored as adding $160B-$367B to deficit | Score contributed to Manchin's opposition; bill failed; pared-down Inflation Reduction Act passed |
| Big Beautiful Bill (2025) | Score in progress; estimated $3-5T deficit increase | Republicans seeking to reconcile score with deficit-hawk members; Byrd Rule implications critical |
How CBO Scores Shape the Political Fight
For reconciliation bills, CBO's score is binding. If a provision adds to the deficit beyond the budget window, or doesn't have a sufficient budget connection, the Senate Parliamentarian can strike it using the Byrd Rule. Republicans designing their 2025 reconciliation package must structure provisions to survive CBO scoring or face having them removed — which shapes what gets into the bill.
Republicans argue CBO uses "static" or "conventional" scoring that underestimates the economic growth effects of tax cuts. CBO has incorporated some dynamic analysis, but growth assumptions remain disputed. When the 2017 tax cuts were projected to add $1.5T to the deficit, Republicans insisted economic growth would offset much of that cost. The growth effects were real but smaller than predicted.
Because CBO only scores over a 10-year window, policies that expire before year 10 cost less in the official score. This is why the 2017 tax cuts for individuals were written to expire in 2025 — to keep the 10-year score within reconciliation limits. Republicans are now fighting to extend those provisions permanently, which the CBO would score as adding significantly to the long-term deficit.
Frequently Asked Questions
Is the CBO politically biased?
No significant evidence of systematic political bias exists. Both parties have criticized CBO scores when those scores were inconvenient — Republicans attacked CBO over ACA estimates; Democrats attacked CBO when its health coverage estimates conflicted with their messaging. Academic studies have generally found CBO's estimates to be reasonably accurate and methodologically consistent regardless of which party's legislation is being scored.
What is the difference between CBO and OMB?
The CBO is a nonpartisan legislative branch agency that works for Congress. The OMB (Office of Management and Budget) is an executive branch agency that works for the president. OMB prepares the president's budget and oversees executive branch spending. CBO and OMB often produce different estimates for the same legislation, because they use different economic assumptions and methodologies.
Can Congress override a CBO score?
Congress can choose to use different budget rules or assumptions — for example, "assume" that certain spending will never be appropriated, or use a different baseline. However, for reconciliation and Byrd Rule purposes, the CBO score is treated as authoritative by the Senate Parliamentarian. Congress cannot simply order CBO to produce a different score, but legislative designers can structure bills to achieve a more favorable score by changing what the bill actually does.
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