The interest rate your bank quotes is a nominal rate — it doesn't account for inflation. The real interest rate is what you actually earn in purchasing power terms after inflation eats away at the nominal yield. Our real interest rate calculator implements the Fisher equation to convert any nominal rate into a real rate. When inflation runs higher than your nominal yield, your real interest rate is negative — your savings are losing real value even as the dollar balance grows.
Input the headline interest rate from your bank or bond.
Use current CPI or a custom inflation expectation.
See the inflation-adjusted real return.
The Fisher equation by Irving Fisher (1930) expresses the relationship between nominal interest rates, real interest rates, and expected inflation. The exact formula divides (1 + nominal) by (1 + inflation); the simple approximation (nominal − inflation) works well at low rates but understates the gap at higher rates. Always use the exact formula when accuracy matters.
Real Rate = ((1 + Nominal) / (1 + Inflation)) − 1
When inflation > nominal rate, real interest is NEGATIVE — you lose purchasing power
US savings accounts often have negative real rates, especially during high-inflation periods
Long-run US T-Bill real rate averages around 1%; long-run stock real rate ~7%
Real interest rates drive economic decisions — borrowing is cheaper when real rates are negative
TIPS (Treasury Inflation-Protected Securities) lock in a known real yield
Use the Fisher exact formula for high-inflation environments where the approximation breaks down
The nominal interest rate your bank advertises tells only half the story. What truly matters for your wealth is the real interest rate — the return you earn after subtracting inflation. Economist Irving Fisher formalized this relationship in the Fisher equation: real rate equals (1 + nominal rate) divided by (1 + inflation rate), minus one. When inflation exceeds the nominal rate, your real return turns negative, meaning your savings lose purchasing power even as the dollar balance grows. For example, a savings account paying 4.5% APY with 3% inflation yields a real return of roughly 1.46%, not 1.5% — the compounding matters. Real interest rates profoundly influence economic decisions: negative real rates encourage borrowing and spending, while positive real rates reward saving. The Federal Reserve watches real rates closely when setting monetary policy. For investors, comparing real yields across assets — Treasury Inflation-Protected Securities (TIPS), CDs, bonds, and savings accounts — reveals which instruments genuinely grow wealth versus merely keeping pace with rising prices.
Whenever you compare investments, loans, or savings options, you should be comparing real rates, not nominal. A 6% savings account during 2% inflation is much better than a 7% account during 4% inflation, even though the nominal rate is lower. Always think in real terms — it's what determines whether your wealth is actually growing.
Data sourced from trusted institutions
All formulas verified against official standards.