TL;DR — The 30-year fixed mortgage rate you see on
Freddie Mac’s weekly survey is not set by the Federal Reserve directly. It
tracks the 10-year U.S. Treasury yield plus a “mortgage spread”
that pays lenders and mortgage-bond investors for prepayment risk and
processing costs. When the 10-year moves, mortgage rates move with a lag.
When the spread widens, mortgages get more expensive even if Treasury yields
don’t budge.
The formula worth memorizing
A useful mental model:
30-year mortgage rate
≈ 10-year Treasury yield + mortgage spread
The 10-year Treasury is the anchor because a 30-year mortgage, in
practice, has an effective life closer to 7–10 years — most
homeowners either refinance or sell long before the loan naturally matures.
So the closest maturity in the risk-free curve, and the one lenders and
mortgage-bond investors watch, is the 10-year, not the 30-year Treasury.
The “mortgage spread” is really two spreads stacked together:
- MBS – Treasury spread (the “secondary” spread).
Mortgages are bundled into agency mortgage-backed securities (MBS) issued
by Fannie Mae, Freddie Mac, and Ginnie Mae. Investors in those MBS demand
extra yield over Treasuries, mainly for prepayment risk —
the risk that homeowners refinance when rates fall, handing the investor
back cash to reinvest at a lower yield. - Primary – secondary spread. What lenders charge
borrowers is a bit higher than what MBS investors receive, to cover loan
origination, servicing, guarantee fees paid to Fannie/Freddie, and lender
profit.
Add the two together and you get the “primary mortgage spread” — the
gap between the 30-year mortgage rate a borrower sees and the 10-year
Treasury yield.
A worked example with this week’s numbers
As of the September 10, 2026 Freddie Mac Primary Mortgage Market Survey,
the 30-year fixed averaged 6.76%. The 10-year Treasury
constant-maturity yield closed the prior day at 4.83%. So
the current mortgage spread is:
6.76% − 4.83% =
1.93 percentage points (193 basis points)
Historically, the 30-year mortgage rate has averaged roughly 1.5 to 2.0
percentage points above the 10-year Treasury — a range you can verify
yourself by comparing the FRED series MORTGAGE30US and DGS10 over the past three decades. Today’s 193 bps sits
just above that historical norm; in late 2023 the spread ballooned above
300 bps as MBS demand collapsed alongside the Fed’s balance-sheet
runoff.
| Series | Rate (%) | As of | Source |
|---|---|---|---|
| 30-year fixed mortgage (Freddie PMMS) | 6.76 | Sep 10, 2026 | Freddie Mac PMMS |
| 15-year fixed mortgage (Freddie PMMS) | 6.09 | Sep 10, 2026 | Freddie Mac PMMS |
| 10-year Treasury yield | 4.83 | Sep 9, 2026 | FRED DGS10 |
| 30-year mortgage – 10-year spread | 1.93 | Sep 10, 2026 | calculated |
| Prior-week 30-year fixed | 6.71 | Sep 3, 2026 | Freddie Mac PMMS |
| Two-week trailing 30-year fixed | 6.66 | Aug 27, 2026 | Freddie Mac PMMS |
Why not the Fed funds rate?
A common misconception: “The Fed cut rates, so my mortgage will get
cheaper next month.” That’s rarely how it works. The federal funds rate is
an overnight rate that banks pay to lend each other reserves. A
30-year mortgage is a 30-year (effectively 7–10 year) commitment. The two
sit at opposite ends of the yield curve.
What the Fed can influence is the whole path of expected
short-term rates — and long-term Treasury yields are essentially a
compounded expectation of those short rates plus a term premium. So the Fed
matters, but the transmission runs through the 10-year Treasury, not
directly. In some cycles, the Fed cuts short rates and the 10-year rises
anyway (bear steepener), and mortgage rates rise with it.
Freddie Mac itself frames its PMMS as a survey of lender-quoted rates on
prime, conforming mortgages — not a rate the Fed sets. Freddie’s
methodology page notes the survey has been based on submitted-application
data from lenders across the country since November 2022.
What moves the mortgage spread?
If you understand the spread, you understand why mortgage rates
sometimes move independently of the 10-year. Four forces drive it:
- Interest-rate volatility. When rates swing violently,
MBS investors face bigger prepayment surprises. They demand extra yield to
hold agency MBS, and that widens the spread. This is the single biggest
reason the mortgage spread blew out to 300 bps in late 2022–2023. - The Fed’s balance sheet. During QE, the Fed bought
agency MBS in size, keeping MBS spreads tight. In quantitative tightening
(QT), the Fed lets MBS roll off — removing a large, price-insensitive
buyer — which widens spreads. The Fed’s own balance-sheet page tracks these
holdings weekly. - The primary-secondary component. This part reflects
lender origination costs, guarantee fees Fannie and Freddie charge, and
competitive pressure between lenders. It moves slowly relative to
markets. - Credit conditions on non-conforming loans. Jumbo
loans and non-QM loans have their own additional spread over the
conforming rate. In banking stress, that jumbo spread widens even if the
agency MBS market is calm.
An analogy
Think of a mortgage rate the way you would a hotel room price. The
“base rate” is the 10-year Treasury — the underlying cost of borrowing
money for a long time. The “resort fee” is the mortgage spread — it
pays for prepayment risk, the packaging into MBS, lender profit, and any
extra cost of the specific loan. The Fed sets the price of a one-night stay
(overnight rates), not the base rate for a 10-year stay. That’s why “the
Fed cut rates” doesn’t automatically shrink your monthly mortgage
payment.
The historical relationship, visualized
Two things stand out on any long chart of these two series. First, the
lines move together with high correlation — almost always in the same
direction week to week. Second, the vertical gap between them widens and
narrows in cycles. It was near 150 bps in the mid-2010s, compressed near
100 bps briefly during the 2020 refi wave (when the Fed was buying MBS
outright), then blew out above 300 bps in 2022–2023 as the Fed pivoted to
QT and rate volatility spiked.
Common mistakes to avoid
- “When the Fed cuts, my mortgage will drop.” Not
reliably. If the market thinks the Fed will cut, that expectation is
already in the 10-year yield. Long rates — and mortgages —
often move before the Fed acts, or against the Fed if inflation
or Treasury supply surprise. - Watching the 30-year Treasury instead of the 10-year.
The 30-year Treasury is a useful sentiment gauge but is not what MBS
investors and lenders benchmark. Watch DGS10. - Assuming the spread is fixed. The primary mortgage
spread has ranged from about 100 bps to more than 300 bps over the past 15
years. A “normal” spread does not really exist — only a wide range. - Confusing the PMMS with daily rate quotes. Freddie
Mac’s Primary Mortgage Market Survey is a weekly Thursday release. Daily
mortgage-rate tickers (from lock desks and rate-quote sites) move around
it and can drift materially in a fast-moving market.
Related concepts to learn next
- Prepayment risk & negative convexity. Why MBS
investors get short an option to the borrower — and why that shapes
the whole spread. - The term premium. Why 10-year Treasury yields are
more than just an average of expected short rates. - QE and QT. How Fed MBS purchases and runoff have
shifted the mortgage spread in every cycle since 2008. - The mortgage lock-in effect. Why millions of
homeowners with sub-4% loans are unwilling to move — and how that
distorts housing supply.
Sources
- Freddie Mac Primary Mortgage Market Survey (PMMS) — weekly 30-year and 15-year rates.
- FRED MORTGAGE30US — historical 30-year fixed rate.
- FRED DGS10 — 10-year Treasury constant-maturity yield.
- Federal Reserve balance-sheet page — agency MBS holdings and runoff.
- Federal Reserve FEDS Notes — research briefs on mortgage rates and spreads.
Disclosure: This article is for informational purposes only and is not investment advice.