Published: 2026-09-28
MBS stands for mortgage-backed securities. They are bonds built from pools of home loans, and the rates lenders offer on new mortgages tend to move with what investors will pay for those bonds.
The Federal Reserve's overnight rate still matters. It does not set your quote by itself. This page explains the link in plain terms. It does not quote today's rates.
Rates and loan terms vary by lender, credit, property, and market conditions. This is educational information, not a loan offer or advice.
What is a mortgage-backed security?
A mortgage-backed security is a bond backed by a pool of home loans. Investors who buy it receive borrowers' principal and interest, passed through each month, after servicing and guarantee fees.
A pool bundles many loans that meet published rules. The investor owns a slice of that pool, not your house. You still pay the servicer, and the servicer forwards what the security is owed.
If you sell or refinance, the loan pays off early and investors must reinvest that principal. That chance is called prepayment risk. It is a reason an MBS is not a copy of a Treasury bond with the same stated maturity.
Who stands behind these securities?
Fannie Mae and Freddie Mac stand behind many securities built from conventional loans that meet their guides. Ginnie Mae guarantees securities built from government-backed loans, including FHA, VA, USDA, and some public housing loans.
Ginnie Mae's program description says it guarantees securities issued by approved lenders. It does not originate your loan. Federal rules also state that Ginnie Mae's guaranty of these mortgage-backed securities is backed by the full faith and credit of the United States. You can read that pledge in 24 CFR 320.1.
Fannie Mae and Freddie Mac guarantees are a different legal promise. They are not the same full-faith-and-credit pledge. Prices of both kinds of securities still move every business day.
Why do retail mortgage rates follow MBS prices?
Retail rates follow MBS prices because many lenders plan to sell the loan, and the sale price has to cover the rate they offered you. The bond market is the bid they are writing toward.
Bond math runs in opposite directions. When investors pay a higher price for an MBS, the yield they earn on that price is lower. When they pay less, the yield is higher. A lender that wants to sell into a lower-priced market generally has to offer borrowers a higher note rate to produce a security investors will still buy. When MBS prices rise, the lender often has room to offer a lower note rate and still sell the loan.
The match is close, and it is not exact. Servicing fees, the guarantee fee, and the lender's margin sit between the investor yield and your note rate. Credit, down payment, property type, occupancy, and lock length adjust the quote again. The companion guide on how mortgage rates are actually determined covers that lender-side pricing.
Why doesn't the fed funds rate set the quote alone?
The federal funds rate is what banks charge each other for overnight loans of reserves. A 30-year mortgage is a long-term loan that the borrower can pay off early. Investors price that long, uncertain cash flow, not the overnight loan.
The Federal Open Market Committee sets a target for that overnight rate. Its decisions can move MBS prices, because they change expectations for inflation, for other bonds, and for how fast homeowners will refinance. In some periods the Fed has also bought and sold bonds, which changes demand for MBS directly.
A change in the overnight target does not copy itself onto a 30-year quote in the same size, or always on the same day. Traders may already have built the decision into bond prices. A surprising statement can move MBS prices even when the rate move was expected. Retail quotes can rise on a day the Fed cuts, because the MBS market moved.
That is why a headline about the overnight rate is an incomplete explanation of a mortgage quote. It is not a forecast.
What can you do with this when you shop?
Use the MBS story to read a moving quote. Compare written offers rather than the bond headline.
Ask what day and what lock length the quote assumes. A Monday quote and a Thursday quote are a weak pair if MBS prices moved. A short lock and a long lock are different prices, because the lender is holding a number while the market can keep trading.
Get Loan Estimates on the same day when you can, for the same loan type, points, and lock length. The note rate on that form is used for principal and interest. A lock has an end date. If the appraisal, credit, or occupancy changes, the price can change with the file.
The payment calculator on HomeMortgageOnline turns a rate you type into a principal-and-interest figure. That is arithmetic, not a live quote and not a prediction. The site does not take applications or lock rates. For the pricing steps, stay with the rates guide.
Disclaimer: this guide is for general education. HomeMortgageOnline is not a lender, broker, or loan originator. It does not take applications, lock rates, or give financial advice. Real offers vary by credit, down payment, loan type, points, fees, and market conditions.
Sources
- Ginnie Mae's program description - https://www.ginniemae.gov/about-us/what-we-do/programs
- 24 CFR 320.1 - https://www.ecfr.gov/current/title-24/subtitle-B/chapter-III/part-320/subpart-A