Apply 3.8% NIIT to S-corp/partnership income. Raises ~$250B over 10 years.
Published score -$250.0B; this estimate is 0.0% away (calibrated reference). Calibrated to reproduce -$250B (JCT (Build Back Better)) — agreement is by construction, not an independent test.
Typical error for this kind of policy: -$296.5B to -$203.5B, from 8 out-of-sample payroll cases.
Out-of-sample accuracy, payroll: 8 pre-registered rows miss their published scores by 18.6% on average (median 16.4%), worst 34.6% — 4 of the 8 fall inside the average. On this figure that is -$296.5B to -$203.5B typical, -$336.5B to -$163.5B 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.
| Fiscal year | Revenue | Deficit, conventional | Macro feedback | Debt service | Deficit, dynamic |
|---|---|---|---|---|---|
| 2026 | +$25.0B | -$25.0B | -$4.4B | -$1.0B | -$21.6B |
| 2027 | +$25.0B | -$25.0B | -$5.0B | -$2.0B | -$22.0B |
| 2028 | +$25.0B | -$25.0B | -$4.3B | -$3.0B | -$23.7B |
| 2029 | +$25.0B | -$25.0B | -$3.3B | -$4.0B | -$25.7B |
| 2030 | +$25.0B | -$25.0B | -$2.4B | -$5.0B | -$27.6B |
| 2031 | +$25.0B | -$25.0B | -$1.7B | -$6.0B | -$29.3B |
| 2032 | +$25.0B | -$25.0B | -$1.2B | -$7.0B | -$30.8B |
| 2033 | +$25.0B | -$25.0B | -$0.8B | -$8.0B | -$32.2B |
| 2034 | +$25.0B | -$25.0B | -$0.5B | -$9.0B | -$33.5B |
| 2035 | +$25.0B | -$25.0B | -$0.4B | -$10.0B | -$34.6B |
| Income group | Returns | Average change | Share of income | Share of total | Paying more | Paying less | Tax rate before | Tax rate after |
|---|---|---|---|---|---|---|---|---|
| Lowest Quintile | 62.8M | $0 | 0.00% | 0.0% | 0.0% | 0.0% | 2.6% | 2.6% |
| Second Quintile | 35.4M | $0 | 0.00% | 0.0% | 0.0% | 0.0% | 5.8% | 5.8% |
| Middle Quintile | 26.0M | $0 | 0.00% | 0.0% | 0.0% | 0.0% | 8.3% | 8.3% |
| Fourth Quintile | 16.8M | $0 | 0.00% | 0.0% | 0.0% | 0.0% | 11.2% | 11.2% |
| Top Quintile | 20.3M | +$3,299 | 0.66% | 100.0% | 61.7% | 0.0% | 20.3% | 20.8% |
Approximate bracket method: this policy cannot run through the return-level microsimulation, so read the shape as directional rather than as a validated table. Groups are ranked by adjusted gross income per return. Average change is in dollars per return; positive means the group pays more tax.
| Fiscal year | GDP level | Jobs | Unemployment | 10-year rate | GDP change, deficit | Interest, deficit |
|---|---|---|---|---|---|---|
| 2026 | -0.063% | -40K | +0.03 pt | -0.00 pt | +$4.4B | -$1.0B |
| 2027 | -0.072% | -46K | +0.04 pt | -0.01 pt | +$5.0B | -$2.0B |
| 2028 | -0.062% | -40K | +0.03 pt | -0.01 pt | +$4.3B | -$3.0B |
| 2029 | -0.048% | -30K | +0.02 pt | -0.01 pt | +$3.3B | -$4.0B |
| 2030 | -0.035% | -22K | +0.02 pt | -0.01 pt | +$2.4B | -$5.0B |
| 2031 | -0.024% | -16K | +0.01 pt | -0.02 pt | +$1.7B | -$6.0B |
| 2032 | -0.017% | -11K | +0.01 pt | -0.02 pt | +$1.2B | -$7.0B |
| 2033 | -0.011% | -7K | +0.01 pt | -0.02 pt | +$0.8B | -$8.0B |
| 2034 | -0.008% | -5K | +0.00 pt | -0.02 pt | +$0.5B | -$9.0B |
| 2035 | -0.005% | -3K | +0.00 pt | -0.03 pt | +$0.4B | -$10.0B |
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: -$250.0B + $24.1B - $55.0B = -$280.9B.
| Model | Ten-year deficit effect | Method |
|---|---|---|
| CBO-Style | -$250.0B | Static + ETI behavioral response + optional FRB/US dynamic feedback |
| TPC-Microsim Pilot | Cannot score this | OASDI wage-cap / donut-hole reforms are not in the microsim tax calculator (NIIT-only payroll edges may map in a later sprint). |
No pilot model returned distributional output; the comparison is aggregate-only.
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.
Cite asWilse-Samson, Laurence. “Expand NIIT.” Fiscal Policy Calculator, CBO February 2026 baseline, FY2026-2035. https://fiscal.lwilsesamson.com/explore/niit-expand