Real vs Nominal Interest Rates: TIPS and Breakevens

Key Takeaways

• Real rate approximately equals nominal rate minus expected inflation (Fisher equation); at high values, use the multiplicative form to avoid meaningful error.
• TIPS yields are observable real yields, their principal adjusts with CPI-U, so the coupon is paid on an inflation-adjusted base.
• Breakeven inflation equals nominal Treasury yield minus matching-maturity TIPS yield, a market-implied expected inflation measure.
• TIPS use CPI-U, not PCE; comparing TIPS breakevens to the Fed's 2% PCE target requires a 30–50 bps structural adjustment.

What It Is

A nominal interest rate is the rate a lender charges or a bond pays without adjusting for changes in purchasing power. If a 10-year Treasury yields 4.2 percent, that 4.2 percent is nominal. A real interest rate subtracts expected inflation from the nominal rate to show the growth in purchasing power you actually earn.

Both rates matter, but for different questions. Nominal rates drive mortgage payments, bond coupons, and interest expense on debt. Real rates drive long-term investment decisions, currency flows, and central-bank policy stances.

The Intuition

Suppose a one-year CD pays 5 percent and inflation over the same year runs at 4 percent. Your balance grows by 5 percent in dollars, but prices rose by 4 percent, so your ability to actually buy things grew by only about 1 percent. The nominal return looks generous. The real return is modest.

Central banks, savers, and corporate planners care about the real rate because it reflects the true cost of capital. A 10 percent mortgage feels crushing when inflation is 2 percent, and almost free when inflation is 12 percent, which is why the 1970s inflation surge effectively bailed out fixed-rate borrowers.

How It Works

The relationship between nominal rates, real rates, and expected inflation is captured by the Fisher equation:

(1 + nominal) = (1 + real) * (1 + expected inflation)

For small numbers, a useful approximation is:

real rate ~= nominal rate - expected inflation

Where:

• nominal rate: the quoted yield or interest rate
• real rate: the inflation-adjusted return
• expected inflation: the market's forecast of future inflation over the same horizon

You can observe real yields directly in the market through Treasury Inflation-Protected Securities (TIPS). The principal of a TIPS bond adjusts with CPI, so its coupon is paid on an inflation-adjusted base. The yield a TIPS trades at is therefore a real yield.

Subtracting the TIPS yield from the matching-maturity nominal Treasury yield gives you the breakeven inflation rate, which the Federal Reserve Bank of St. Louis describes as a market-implied measure of expected inflation:

breakeven inflation = nominal Treasury yield - TIPS yield

If 10-year nominal yields are 4.20 percent and 10-year TIPS yield 1.90 percent, the 10-year breakeven is 2.30 percent. That is roughly what bond markets expect CPI to average over the next decade.

Worked Example

Suppose you are weighing a 2-year corporate bond at 5.50 percent. You pull up the FRED data: 2-year nominal Treasuries yield 4.50 percent, 2-year TIPS yield 1.80 percent, giving a 2.70 percent breakeven.

Implied real yield on your corporate: 5.50 - 2.70 = 2.80 percent.

That 2.80 percent is what you should earn in purchasing-power terms if inflation expectations hold. If you think inflation will actually run at 4.0 percent instead of 2.70 percent, your expected real yield falls to 1.50 percent and the bond looks much less attractive. Comparing across assets on a real basis is how professional allocators avoid money illusion.

Common Mistakes

1. Using realized inflation instead of expected inflation. The Fisher equation is forward looking. Plugging in last year's CPI to judge whether today's nominal rate is attractive is a classic error. What matters is the inflation rate over the life of the investment, which is unobservable and must be estimated (often from TIPS breakevens or surveys).

2. Confusing ex-ante and ex-post real rates. The ex-ante real rate uses expected inflation at the time of the investment. The ex-post real rate uses inflation that actually occurred. They are almost never equal. Bond traders price ex-ante; economists evaluate ex-post. Mixing them produces bad conclusions.

3. Forgetting that TIPS use CPI, not PCE. TIPS principal adjustments follow the non-seasonally-adjusted CPI-U. The Fed's preferred inflation gauge is PCE, which usually runs 30 to 50 basis points below CPI. If you are comparing TIPS breakevens to a 2 percent PCE target, the two series are on different scales.

4. Ignoring the liquidity premium in TIPS. Fed research notes that TIPS yields include a liquidity premium that can be large, historically around 1 percent in the early years of the market and elevated again during stress episodes. A rise in breakevens can reflect worsening TIPS liquidity rather than higher inflation expectations.

5. Treating the approximation as exact. The shortcut real = nominal - inflation works well near zero but drifts when either number is large. At 10 percent nominal and 8 percent inflation, the exact Fisher equation gives 1.85 percent real, not 2.0 percent. Use the multiplicative form whenever the numbers get big.

Frequently Asked Questions

What is the difference between real and nominal interest rates? The nominal rate is the headline number on a bond or loan. The real rate adjusts for inflation to show actual purchasing power growth. A 5% nominal yield with 4% inflation gives roughly 1% real return, your dollars grow 5%, but prices rose 4%, so your buying power grew only 1%.

What are TIPS and how do they show real yields? Treasury Inflation-Protected Securities are bonds whose principal adjusts with CPI-U. Because the coupon is paid on an inflation-adjusted base, the yield a TIPS bond trades at is a real yield, already inflation-stripped. Investors do not need to estimate inflation; the CPI adjustment does it automatically.

What is the breakeven inflation rate? The breakeven inflation rate equals the nominal Treasury yield minus the matching-maturity TIPS yield. If the 10-year nominal is 4.20% and the 10-year TIPS yields 1.90%, the market implies 2.30% average CPI over the next decade. It is the market's best real-time inflation forecast, though it includes a TIPS liquidity premium that can distort it during stress.

Why does the TIPS breakeven not equal the Fed's 2% target when the market seems well-anchored? The Fed targets 2% PCE inflation, not CPI. TIPS principal adjusts with CPI-U, which structurally runs 30–50 basis points above PCE. So even if breakevens read 2.30%, the market may effectively be pricing PCE near 1.80–2.00%, roughly on target. Comparing breakevens directly to the PCE target without this adjustment overstates apparent inflation expectations.

When does the Fisher approximation break down? The shortcut (real ≈ nominal − inflation) works well when both numbers are small. At 10% nominal and 8% inflation, the approximation gives 2.0% real; the exact Fisher equation gives 1.85%. The error grows with the magnitude of the numbers, so use the multiplicative form during high-inflation episodes for precise analysis.

Sources

1. Federal Reserve Board. "TIPS Yield Curve and Inflation Compensation." https://www.federalreserve.gov/data/yield-curve-tables/feds200805_1.html
2. Federal Reserve Board. "Tips from TIPS: Update and Discussions." FEDS Notes, May 2019. https://www.federalreserve.gov/econres/notes/feds-notes/tips-from-tips-update-and-discussions-20190521.html
3. Corporate Finance Institute. "Fisher Equation." https://corporatefinanceinstitute.com/resources/economics/fisher-equation/
4. U.S. Department of the Treasury. "Treasury Inflation-Protected Securities (TIPS)." https://www.treasurydirect.gov/marketable-securities/tips/

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.