How Mortgage-Backed Securities Affect Your Rate

Mortgage rates don't move in lockstep with the Federal Reserve. They move with the mortgage-backed securities (MBS) market, which is why rates can shift even on days the Fed does nothing at all.

What MBS actually are

When a lender originates a mortgage, it's typically bundled together with similar loans and sold to investors as a mortgage-backed security. The price investors are willing to pay for these bundles, traded daily like bonds, is what actually determines the interest rate offered to new borrowers. When MBS prices rise, rates tend to fall. When MBS prices fall, rates tend to rise.

Why this matters more than Fed announcements

The Federal Reserve sets the short-term federal funds rate, which influences things like credit cards and auto loans directly. Mortgage rates respond instead to the bond market's expectations about inflation, economic growth, and future Fed policy, all priced into MBS trading in real time. This is why mortgage rates sometimes move before a Fed meeting even happens, or barely move at all after one, depending on whether the market had already priced in the expected outcome.

What actually moves the MBS market day to day

Inflation reports, employment data, and Treasury yield movements are the biggest daily drivers. A hotter-than-expected inflation report typically pushes rates up the same day, while weaker economic data usually pushes them down, because it signals room for future Fed rate cuts.

Why this matters for timing your refinance

Rates can move meaningfully within a single week based on economic data releases. Watching the calendar for major reports, rather than trying to guess the market day to day, is a more reliable way to think about timing a rate lock than watching Fed meeting dates alone.