The Unseen Interest Rate: How Residual Market Surcharges Erode Homebuyer Purchasing Power
At a $120,000 income and a 28% PITI cap, moving from a $2,400 HO-3 planning premium to the state residual mid cuts max purchase price by $12,349–$53,386 across five CA / FL / TX counties — the same hit as roughly 42–154 basis points on a 6.5% 30-year mortgage.
Open Data Collective Editorial · Published 2026-10-16 · Updated 2026-10-16 · 11 min read
Admitted carriers have pulled back in California wildfire zones and along the Florida coast. When a buyer lands in the California FAIR Plan or Florida Citizens, the premium is not just a line item — it competes with principal and interest inside the same DTI box.
This brief holds income, rate, and down payment fixed, then swaps only the insurance bill. County tax rates come from the same dataset as the escrow calculator. Residual mids come from our state insurance-market table.
One-sentence finding
At a $120,000 income and a 28% PITI cap, moving from a $2,400 HO-3 planning premium to the state residual mid cuts max purchase price by $12,349–$53,386 across five CA / FL / TX counties — the same hit as roughly 42–154 basis points on a 6.5% 30-year mortgage.
Five-county purchasing-power table
Income $120,000, 28% PITI cap, 6.5% 30-year, 20% down.
| Market | Tax rate | Residual /yr | Max price, admitted | Max price, residual | Price gap | Rate bump |
|---|---|---|---|---|---|---|
Riverside County, CA California FAIR Plan Related page | 0.97% | $4,800 | $443,317 | $409,216 | $34,101 | 91 bps |
Los Angeles County, CA California FAIR Plan Related page | 0.75% | $4,800 | $457,622 | $422,420 | $35,202 | 88 bps |
Miami–Dade, FL Citizens Property Insurance Corporation Related page | 1.05% | $6,200 | $438,334 | $384,948 | $53,386 | 152 bps |
Hillsborough (Tampa), FL Citizens Property Insurance Corporation Related page | 1.18% | $6,200 | $430,472 | $378,043 | $52,429 | 154 bps |
Harris County, TX Texas FAIR Plan Association Related page | 2.03% | $3,400 | $385,287 | $372,938 | $12,349 | 42 bps |
Average price gap $37,493 · average equivalent bump 105 bps. Admitted planning premium is $2,400/yr in every row.
Method
Closed-form PITI cap. No black-box affordability score.
- Budget: monthly PITI ≤ income / 12 × 0.28. That is the conforming front-end ratio. A 43% back-end cap is assumed to absorb other debts, so we do not lend the full 43% to housing.
- Loan: 30-year fixed at 6.5%, 20% down. Price solves so principal, interest, tax, and insurance equal the budget.
- Tax: county effective rates from
COUNTY_REAL_ESTATE_DATA(Riverside, Los Angeles, Miami–Dade, Hillsborough, Harris). - Insurance: admitted floor $2,400; residual mid from
STATE_MARKET_TABLE. - Basis points: the higher note rate that, with the admitted premium, supports the same price as the residual premium at 6.5%.
Directional model, not a lender pre-approval or carrier quote. Admitted premium is a $2,400 HO-3 planning floor. Residual premium is the state-table mid (FAIR Plan or Citizens). PITI is capped at 28% of a $120,000 gross income with 20% down and a 6.5% 30-year fixed rate. California FAIR Plan is typically fire-only; a DIC wrap is extra and is not added on top of the residual mid.
Site launch reference 2026-06-13. Methodology.
What to run before you write an offer
- Get an admitted quote and a residual quote for the same dwelling limit.
- Stress the payment in the escrow calculator using the higher premium, not the listing’s year-1 estimate.
- In California high-fire ZIPs, open a FAIR Plan ZIP page and ask whether a DIC wrap is required.