Attributing the FY2026 Federal Deficit to the 2025 Reconciliation Act (OBBBA)

The federal budget deficit was USD 1,992.5 billion in fiscal year 2026, which is USD 217.1 billion (12.2%) above FY2025. This paper estimates how much of the deficit, and of its increase, traces to the 2025 reconciliation act, P.L. 119-21 (OBBBA). It uses the Congressional Budget Office (CBO) and Joint Committee on Taxation (JCT) scores of the act, JCT's current-policy baseline, CBO's January 2025 and February 2026 projections, and Treasury and Bureau of Economic Analysis (BEA) data. The answer depends on how the question is framed. As a level, the act's scored FY2026 effect is USD 486.8 billion against a current-law baseline (24% of the deficit) or USD 275.7 billion against a current-policy baseline (13.8%). As a change from FY2025, the scored effect rises by USD 303.9 billion, or 140% of the increase, and that figure includes the non-recurrence of a one-time FY2025 student-loan entry, scored at USD 150.0 billion and recorded at USD 131 billion in September 2025, which is part of the act's effect. As a memo, the author's own subtraction of the scored amount gives USD 153.8 billion, or 71%. Removing the act's FY2026 effect gives a deficit of USD 1,491 billion to USD 1,717 billion (4.6% to 5.3% of GDP), with a base case of USD 1,506 billion (4.7%), against 6.2% actual. Corporate income tax receipts fell USD 70.7 billion (15.6%); the evidence supports the act as the largest single driver but does not support attributing the entire decline to it. All effects attributed to the act are enactment-date static projections, not measured outcomes.