The 30-year jumbo mortgage index stood at 7.337% on October 1, 2026, slightly below the 7.368% 30-year conforming index in RateZip's mortgage-rate dashboard. The gap was 0.031 percentage point, or 3.1 basis points, in favor of the jumbo index.
That small difference challenges the idea that a jumbo index must always sit above a conforming one. It does not prove that moving above a conforming loan limit will lower a particular borrower's rate. The two Optimal Blue indexes, carried by FRED, summarize different pools of locked loans.
| October 1 observation | 30-year conforming | 30-year jumbo |
|---|---|---|
| Index interest rate | 7.368% | 7.337% |
| Change from a week earlier | +12 basis points | +9 basis points |
| Change from a year earlier | +111 basis points | +87 basis points |
Weekly and annual changes are rounded to whole basis points. Index interest rates are not APRs or quotes for an identical applicant.
The dollar difference is small when amount and term are fixed
To isolate the rate arithmetic, applying these rates to the same hypothetical $400,000 balance over 30 years produces monthly principal and interest of $2,760.79 and $2,752.35, a difference of $8.44. This deliberately holds the amount fixed; it does not classify a $400,000 loan as jumbo or establish eligibility. Taxes, insurance, mortgage insurance, points and fees are excluded.
An actual jumbo borrower usually is not choosing between two otherwise identical index loans. Loan size, property location, credit, down payment, cash reserves, occupancy and lender terms affect available offers. A larger balance can raise the payment substantially even when its interest rate is slightly lower.
The index does not explain the cause
This snapshot contains no lender funding-cost records, deposit relationships or matched applications. It cannot show that a bank intentionally subsidized jumbo lending or that a particular borrower profile caused the gap. Those are possible research questions, not findings from the table.
The practical comparison remains a set of actual Loan Estimates using consistent assumptions. A 3.1-basis-point index difference is too narrow a basis for a borrowing strategy without considering closing costs and eligibility. The CFPB's guide to comparing loan offers provides the relevant framework: compare the offers the borrower can obtain, including their costs, rather than selecting a category because its broad index happens to be lower.
RateZip is operated by Peklava LLC, DBA RateZip, a licensed mortgage broker (NMLS ID 1592292). We are compensated by some of the partners shown, which may affect which offers appear and where. It does not affect our reporting or recommendations. See our editorial standards.