FY2026-2035 · CBO February 2026 baseline

Flat Tax Reform

Lower all rates by 5pp (illustrative)

Ten-year deficit effect, conventional+$6,424.9Badds to the deficit
With macroeconomic feedback and debt service+$7,389.6BFRB/US-Lite (Federal Reserve calibrated)
Checked against

No published score for this exact policy is on file.

Typical error for this kind of policy: +$5,441.9B to +$7,408.0B, from 11 out-of-sample ordinary rate change cases.

Out-of-sample accuracy, ordinary rate change: 11 pre-registered rows miss their published scores by 15.3% on average (median 15.0%), worst 40.6% — 6 of the 11 fall inside the average. On this figure that is +$5,441.9B to +$7,408.0B typical, +$3,816.4B to +$9,033.5B at the worst row. Read off the out-of-sample tier only — not the calibrated tiers, whose agreement is by construction. It is the observed spread of this model against published scores for this class of policy, not a confidence interval.

Year by year

billions, conventional
Fiscal yearRevenueDeficit, conventionalMacro feedbackDebt serviceDeficit, dynamic
2026-$612.3B+$535.8B+$86.2B+$21.4B+$471.0B
2027-$639.5B+$559.5B+$91.4B+$43.8B+$511.9B
2028-$665.4B+$582.2B+$72.1B+$67.1B+$577.2B
2029-$691.2B+$604.8B+$50.0B+$91.3B+$646.1B
2030-$717.7B+$628.0B+$31.9B+$116.4B+$712.4B
2031-$745.0B+$651.9B+$19.0B+$142.5B+$775.3B
2032-$773.1B+$676.4B+$10.5B+$169.5B+$835.5B
2033-$802.2B+$702.0B+$5.2B+$197.6B+$894.4B
2034-$832.5B+$728.4B+$2.1B+$226.8B+$953.1B
2035-$864.0B+$756.0B+$0.3B+$257.0B+$1,012.6B

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Who pays

first year, by income group
Total tax change, 2026-$516.4Bpeople pay less
Returns paying more0.0%
Returns paying less79.2%
Income groupReturnsAverage changeShare of incomeShare of totalPaying morePaying lessTax rate beforeTax rate after
Lowest Quintile56.4M-$185-1.11%2.0%0.0%42.9%-3.5%-4.7%
Second Quintile37.8M-$1,311-2.87%9.6%0.0%98.1%3.5%0.7%
Middle Quintile28.4M-$2,827-3.69%15.6%0.0%99.2%7.4%4.0%
Fourth Quintile19.5M-$5,112-4.25%19.3%0.0%99.3%9.9%6.0%
Top Quintile18.3M-$15,050-4.46%53.5%0.0%99.1%20.3%16.8%

Return-level microsimulation on CPS ASEC tax units calibrated to IRS data: the validated distributional tier. Groups are ranked by adjusted gross income per return. Average change is in dollars per return; positive means the group pays more tax.

Economic effects

difference from the CBO baseline
GDP, summed over the window+5.27percent-years
Jobs at the largest effect+836K
Deficit effect of the GDP change-$368.8Bmore tax collected
Deficit effect of interest on the debt+$1,333.5Bmore debt, more interest
Fiscal yearGDP levelJobsUnemployment10-year rateGDP change, deficitInterest, deficit
2026+1.232%+788K-0.62 pt+0.06 pt-$86.2B+$21.4B
2027+1.306%+836K-0.65 pt+0.12 pt-$91.4B+$43.8B
2028+1.030%+659K-0.52 pt+0.18 pt-$72.1B+$67.1B
2029+0.714%+457K-0.36 pt+0.24 pt-$50.0B+$91.3B
2030+0.456%+292K-0.23 pt+0.31 pt-$31.9B+$116.4B
2031+0.272%+174K-0.14 pt+0.38 pt-$19.0B+$142.5B
2032+0.150%+96K-0.08 pt+0.45 pt-$10.5B+$169.5B
2033+0.074%+48K-0.04 pt+0.53 pt-$5.2B+$197.6B
2034+0.030%+19K-0.01 pt+0.61 pt-$2.1B+$226.8B
2035+0.005%+3K-0.00 pt+0.69 pt-$0.3B+$257.0B

FRB/US-Lite (Federal Reserve calibrated). Demand effects fade over five to seven years as monetary policy responds; there is no supply-side channel. The dynamic score is the conventional score, plus the deficit effects of the GDP change and of interest on the debt: +$6,424.9B - $368.8B + $1,333.5B = +$7,389.6B.

Other scoring models

exploratory
ModelTen-year deficit effectMethod
CBO-Style+$6,424.9BStatic + ETI behavioral response + optional FRB/US dynamic feedback
TPC-Microsim Pilot+$5,413.4BSingle-year CPS-style microsimulation with flat-horizon annualization and quintile distribution output. Default microdata is already SOI-calibrated (top tail included); no separate top-tail augmentation applied. Maps to microsim reforms: income_rate_change, income_rate_change_threshold. Income-tax rate changes are applied to every ordinary bracket (threshold $0) in the pilot microsim.

CBO-Style is the model behind the headline above. The TPC-style microsimulation is a pilot: where the two disagree, the gap tells you how much the answer depends on method. It is not an official range.

Limitations

Cite asWilse-Samson, Laurence. “Flat Tax Reform.” Fiscal Policy Calculator, CBO February 2026 baseline, FY2026-2035. https://fiscal.lwilsesamson.com/explore/across-the-board-rate-cut-5pp