What Is OBMMI? The Index Behind Our Rates
Every rate on the RallyRates board is anchored to a benchmark called OBMMI — the Optimal Blue Mortgage Market Indices. It's the number we show as the day's market rate, and it's worth understanding, because it's built very differently from the rate you see quoted in a news headline.
What OBMMI actually measures
OBMMI is derived from real locked rates — the actual prices borrowers accepted, pulled from the loan-pricing engine that a large share of U.S. lenders run their quotes through. It isn't a survey and it isn't an advertisement. When a borrower locks a 30-year conforming loan, that lock becomes one of the data points behind the index. Averaged across the country each day, that produces a genuinely market-based picture of where rates are sitting — by product (30-year conforming, 15-year, FHA, VA, jumbo), not just one blended figure.
How it differs from the Freddie Mac weekly survey
The rate most news stories quote is the Freddie Mac PMMS — a survey of lenders published once a week, on Thursdays, historically for the conventional conforming 30-year only. A survey has two built-in lags: it's weekly, so it can be days stale in a fast-moving market, and it reflects what lenders say rather than what borrowers actually locked. OBMMI, by contrast, updates daily and is drawn from locks. The two usually track each other closely, but when rates are moving the daily lock-based index turns first — which is exactly why we benchmark to it.
Why it still isn't the rate you'll be quoted
OBMMI is an average of everyone. Your personal rate is built from your own file — credit score, loan-to-value, loan amount, property type, points paid — plus your lender's margin, locked on a specific day. So the index is the right tool for one job: seeing where the market is and which way it's moving. It is not a quote. We walk through that gap in detail in why the headline rate isn't yours, and the mechanics of how a single rate gets built in how mortgage rates are set.
How RallyRates uses it
We pull OBMMI daily (via the St. Louis Fed's FRED, which redistributes it) and show it as the Market Benchmark layer on the board and in the RallyRates Index. Because it's a neutral, market-wide reference that no lender can influence, it's the honest yardstick to shop any individual quote against — if a lender's offer is well above the day's OBMMI for your product, that's your cue to ask why.
Common questions
What does OBMMI stand for?
The Optimal Blue Mortgage Market Indices. They are a family of daily mortgage-rate indices built from actual locked rates flowing through Optimal Blue's loan-pricing engine, broken out by loan product.
Is OBMMI the same as the Freddie Mac rate?
No. Freddie Mac's PMMS is a weekly lender survey; OBMMI is a daily index built from real locks. They track closely over time, but OBMMI updates every business day and tends to move first when the market shifts, because it reflects locks rather than a once-a-week survey.
Why doesn't OBMMI match the rate my lender quoted me?
Because it's a nationwide average across all borrowers and lenders. Your quote reflects your specific credit, down payment, loan amount and points, plus your lender's margin on a given day. Use OBMMI to see where the market is, not as a quote you can lock.
Where does RallyRates get its OBMMI data?
From the Federal Reserve's FRED service, which redistributes the Optimal Blue indices with attribution. We read it daily and show it as the Market Benchmark layer; the figure is free to reuse with credit (see our License page).
By L.W. Martin, Founder — 20 years in the mortgage business, including 15 running his own brokerage. About → · Updated September 2026.