How to Use the Real Interest Rate Calculator
A savings or CD rate that looks attractive on paper can still leave you worse off in real terms once inflation is factored in. This calculator takes your nominal interest rate and expected inflation rate and computes the exact real interest rate using the Fisher equation, alongside the commonly used simple approximation (nominal rate minus inflation).
The Fisher equation divides (1 + nominal rate) by (1 + inflation rate) and subtracts 1, which correctly captures how the two rates compound against each other. At low rates and low inflation, the simple approximation is close enough, but the gap between the two methods widens as either number gets larger.
If your real interest rate comes out negative, it means inflation is running higher than your nominal rate — your money is technically earning interest, but its actual purchasing power is shrinking. In periods like this, it's worth comparing savings accounts against other assets that may better keep pace with inflation.
Frequently Asked Questions
The nominal rate is the stated rate a bank advertises. The real interest rate adjusts for inflation to show how much your purchasing power actually grows. High inflation can turn a decent nominal rate into a low or negative real return.
The simple subtraction (nominal minus inflation) is only an approximation. The Fisher equation accounts for the compounding interaction between the two rates, so the gap grows larger as rates and inflation rise.
It means inflation is outpacing your interest earnings, so money sitting in that account is actually losing purchasing power over time, even though the account balance itself is growing.