Understanding Mortgage-Backed Securities and Their Effect on Your Rate

When you get a mortgage, your loan doesn’t usually stay with your original lender. Most conventional loans are bundled with thousands of others into mortgage-backed securities (MBS) and sold to investors. That secondary market — far more than any single lender’s decision — is what ultimately sets the rate you’re offered.

How it works, in simple terms:

• Lenders originate loans, then sell them into the secondary market to free up capital to lend again
• Loans are pooled into MBS and sold to institutional investors, including pension funds and, at times, the Federal Reserve
• The price investors are willing to pay for these securities determines the rate lenders can profitably offer
• When investor demand for MBS is strong, rates tend to fall; when demand weakens, rates tend to rise

What drives investor demand:

• Comparisons to other investments, particularly Treasury bonds, which compete for the same investor dollars
• Expectations for prepayment speed — how quickly borrowers are likely to refinance or pay off loans early
• Overall risk appetite in financial markets during periods of volatility

This is also why your mortgage rate can move even on days with no major economic news — MBS prices shift throughout the trading day based on ordinary supply and demand. You’ll never negotiate directly with the MBS market, but understanding it explains why rates sometimes move for reasons that have nothing to do with your credit profile or your lender.