Interest Rates: How They Work and Move Markets

Key Takeaways

• Real rate equals nominal rate minus expected inflation (Fisher equation); a 5% yield with 6% inflation is a negative real return.
• A 10-year Treasury with duration near 8 loses roughly 8% of its price for every 1 percentage point rise in yield.
• Long rates (10-year, 30-year) are driven by expected future short rates plus term premium, not the Fed funds rate directly.
• An inverted yield curve (10-year minus 2-year negative) has historically preceded most U.S. recessions, with a variable lag.

What It Is

An interest rate is usually quoted as a percent per year and attached to a debt instrument: a bank loan, a mortgage, a credit card balance, a corporate bond, a Treasury bill. The rate compensates the lender for three things: the time value of money, expected inflation over the life of the loan, and the risk the borrower may not pay back in full.

There is no single "interest rate." The Federal Reserve's H.15 release publishes dozens: the federal funds rate, Treasury yields from one month to thirty years, mortgage rates, commercial paper rates, and more. Each applies to a different maturity, credit quality, and market.

The Intuition

Interest rates are the gravitational field of finance. A higher risk-free rate pulls down the present value of future cash flows, which means lower equity multiples and lower bond prices. A lower rate does the opposite. Borrowing costs, savings returns, currency levels, and housing affordability all follow the same force.

The Federal Reserve does not set most rates directly. It sets a target range for a single overnight rate, the federal funds rate, and the rest of the market prices off that anchor plus expectations about where it is heading.

How It Works

Start with the distinction between nominal and real rates. The nominal rate is the sticker number on a bond or loan. The real rate is what you actually earn in purchasing power after inflation. The Fisher equation links the two.

(1 + i) = (1 + r) * (1 + pi_e)

Where i is the nominal rate, r is the real rate, and pi_e is expected inflation. A useful approximation when rates and inflation are both low is:

r  ~  i - pi_e

A 5 percent nominal yield with 3 percent expected inflation leaves a real return of about 2 percent.

Next, the maturity dimension. Short rates refer to overnight or money-market instruments: the federal funds rate, the Secured Overnight Financing Rate (SOFR), three-month Treasury bills. Long rates refer to multi-year maturities: the two-year, five-year, ten-year, and thirty-year Treasury yields. Short rates are driven mostly by current policy. Long rates are driven by expected future short rates plus a term premium for holding duration risk.

The gap between long and short is the yield curve. FRED publishes the 10-year minus 2-year Treasury spread as T10Y2Y. When the curve inverts, long rates fall below short rates, and historically this has preceded most U.S. recessions, though the lag is variable.

The third dimension is credit risk. A Treasury yield is close to risk-free because the issuer is the U.S. government. A corporate bond yield includes a credit spread over the matched-maturity Treasury to compensate for default risk. Investment-grade spreads are small, high-yield spreads are larger, and both widen in recessions.

Putting it together, the yield on any bond is approximately the risk-free real rate plus expected inflation plus a term premium plus a credit spread.

Worked Example

Suppose the Federal Open Market Committee has set the target range for the federal funds rate at 4.25 to 4.50 percent. The 2-year Treasury yields 4.00 percent, the 10-year yields 4.25 percent, and an A-rated corporate 10-year bond yields 5.00 percent.

What the market is telling you:

• Short rates are expected to drift slightly lower over the next two years (2-year at 4.00 percent is below the policy midpoint of 4.375 percent).
• The curve is only modestly positive (10-year minus 2-year = 25 basis points). Not inverted, but not steep.
• The A-rated credit spread is 75 basis points (5.00 minus 4.25 percent), which is roughly in line with long-run averages for that rating band.

Now apply the Fisher approximation. If breakeven inflation implied by Treasury Inflation-Protected Securities is 2.3 percent, the real 10-year yield is about 4.25 - 2.30 = 1.95 percent. That is the compensation a Treasury investor gets for locking up purchasing power for a decade.

Common Mistakes

1. Confusing nominal with real. A 5 percent savings account feels generous until you realize inflation is running at 6 percent. The real return is negative. Always know which number you are looking at, especially when comparing returns across decades with different inflation regimes.

2. Forgetting bond prices move inversely to yields. If yields rise, the market value of existing fixed-coupon bonds falls. A 10-year Treasury with a duration near 8 loses roughly 8 percent of its price for every 1 percentage point rise in yield. Investors who buy "safe" long bonds without understanding duration often meet this lesson the hard way.

3. Treating the Fed funds rate as "the interest rate." The federal funds rate is an overnight policy rate. It directly anchors other short rates but influences mortgages, corporate bonds, and ten-year yields only indirectly, through expectations and risk premiums. In some cycles, long rates fall while the Fed is still hiking, which confuses observers who expect a one-to-one move.

4. Expecting rates to mean-revert on a fixed schedule. Rates have gone through decade-long trends in both directions. The 1980s started with a Fed funds rate above 15 percent. The 2010s sat near zero for years. Betting that the current level must return to some historical average is a faith-based trade, not an analytical one.

5. Conflating short and long rates. Short rates react to Fed decisions. Long rates react to growth, inflation, and term-premium swings that the Fed only partially controls. An analysis that treats a 10-year yield as a simple function of the policy rate misses the largest part of what drives it.

Frequently Asked Questions

What is the difference between nominal and real interest rates? The nominal rate is the sticker number on a bond or loan. The real rate is what you earn in purchasing power after inflation. The Fisher equation links them: real rate approximately equals nominal rate minus expected inflation. A 5 percent nominal yield with 6 percent inflation produces a negative real return.

Why do bond prices fall when interest rates rise? Existing bonds pay fixed coupons. When new bonds are issued at higher rates, older bonds must trade at a discount to compete. A 10-year Treasury with duration near 8 loses roughly 8 percent of its market value for every 1 percentage point rise in yield, a relationship that surprises many investors who view bonds as "safe."

Does the Fed directly control mortgage rates? No. The federal funds rate is an overnight policy rate that directly anchors other short rates. Thirty-year fixed mortgages are priced off the 10-year Treasury yield plus a credit spread, which is driven by long-run growth and inflation expectations. In some cycles, mortgage rates move very little even as the Fed hikes aggressively.

What is the yield curve and why does it matter? The yield curve plots Treasury yields across maturities. A normal curve slopes upward because investors demand more compensation to lock up money longer. When short rates exceed long rates (inversion), the FRED T10Y2Y spread goes negative, a pattern that has preceded most U.S. recessions, though the lead time varies widely.

What is a credit spread? A credit spread is the extra yield a bond pays above a matched-maturity Treasury to compensate for default risk. Investment-grade spreads are narrow in good times; high-yield spreads are larger and widen sharply in recessions. The total yield on any corporate bond equals the risk-free rate plus term premium plus that credit spread.

Sources

1. Federal Reserve. "Monetary Policy: What Are Its Goals? How Does It Work?" https://www.federalreserve.gov/monetarypolicy/monetary-policy-what-are-its-goals-how-does-it-work.htm
2. Federal Reserve. "The Fed Explained: Monetary Policy." https://www.federalreserve.gov/aboutthefed/fedexplained/monetary-policy.htm
3. Federal Reserve. "H.15 Selected Interest Rates." https://www.federalreserve.gov/releases/h15/
4. Federal Reserve Bank of St. Louis (FRED). "10-Year Treasury Constant Maturity Minus 2-Year Treasury Constant Maturity (T10Y2Y)." https://fred.stlouisfed.org/series/T10Y2Y
5. Corporate Finance Institute. "Fisher Equation." https://corporatefinanceinstitute.com/resources/economics/fisher-equation/

Disclaimer

This article is educational content only and is not financial advice. Nothing here is a recommendation to buy, sell, or hold any security. Consult a licensed advisor before making investment decisions.