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Fundamental analysis

Real interest rate

By Jarosław Wasiński • Published: • Updated:
An interest rate adjusted for inflation. The approximation is nominal rate minus inflation, while the exact relation is (1 + nominal rate) / (1 + inflation rate) − 1. Expected inflation gives an ex-ante measure; realised inflation gives an ex-post measure. Use rates covering the same period.
Example.

The annual nominal rate is 5% and inflation over the same period is 3%. Subtraction approximates 2%; the exact relation (1.05/1.03 − 1) × 100 gives about 1.94%. Forecast inflation produces an ex-ante measure; realised inflation produces ex post.

A consistent horizon

Match inflation to the rate's period: annual inflation is not a direct adjustment to one day's income. Record the price index, currency, compounding and expectation source. A real rate does not remove credit risk.

Approximate and exact calculation

Subtracting inflation is convenient at moderate rates. The exact formula compares the growth in nominal money with the price level. At high inflation the two methods can differ materially.

Application to FX

Comparing real conditions across economies helps examine investor incentives. A rate calculated using current CPI is not automatically a market-implied expected real yield. Premia and forecasts can change without a policy decision.

FAQ

Does positive nominal interest mean positive real interest?

No. If inflation exceeds the nominal return, purchasing power may fall.

Is a real rate an after-tax return?

No. Inflation and tax are separate adjustments; net purchasing-power outcomes may require both.

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Jarosław Wasiński

Editor-in-chief, ForexMechanics.com • Macro & FX analyst

Independent analyst and practitioner with over 20 years of experience in financial markets. Actively involved in Forex since 2007, with a focus on fundamental analysis, OTC market structure, and disciplined capital risk management.

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