Real Interest Rate Calculator — Fisher Equation
Find out what your nominal interest rate is actually worth after inflation. The Fisher equation gives the exact real rate; the classic approximation is just nominal minus inflation.
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Exact real rate using the Fisher equation: (1 + nominal) ÷ (1 + inflation) − 1
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Nominal factor
1 + 6% ÷ 100 = 1.06 - 2
Inflation factor
1 + 3% ÷ 100 = 1.03 - 3
Fisher ratio
1.06 ÷ 1.03 = 1.029126Ratio of the two compound factors — the core of the Fisher equation. - 4
Real interest rate
(1.029126 − 1) × 100 = 2.913 %
How does this calculator work?
Real interest rate = (1 + nominal rate) ÷ (1 + inflation rate) − 1 (Fisher equation). A 6% nominal rate with 3% inflation yields a real rate of ≈2.91%, not 3%. The simple approximation (6% − 3% = 3%) overstates the real rate — the error grows at high inflation.
Formula
How this is calculated
A nominal interest rate is the figure quoted by banks and bonds — it does not account for the fact that inflation erodes purchasing power. If your savings account pays 6% and inflation is 3%, you might think you gained 3% — but the Fisher equation shows the exact real rate is (1.06 / 1.03) − 1 ≈ 2.913%, slightly less than 3%. The gap between the exact and approximate figures grows with higher inflation rates.
The Fisher equation, formulated by economist Irving Fisher in 1930, is the standard way economists convert between nominal and real interest rates. A positive real rate means lending increases purchasing power; a negative real rate (common during high-inflation periods) means lenders are losing real wealth even while receiving nominal payments.
Central banks, bond investors, and businesses use the real rate to assess the true cost of borrowing and the actual return on savings. For example, if inflation exceeds the deposit rate — as happened in many countries in 2022–2023 — depositors face a negative real rate and their purchasing power shrinks despite earning nominal interest.
Frequently asked questions
The approximation (nominal − inflation) is fine for quick estimates when both rates are low (below ~5%). At higher rates, the exact Fisher equation matters — for example, at 20% nominal and 15% inflation, the approximation gives 5% while the exact formula gives 4.35%, a meaningful difference.
Yes — and it frequently is. When inflation exceeds the nominal rate (for example, 2% deposit rate with 5% inflation), the real rate is negative: savers are losing purchasing power. Central banks sometimes deliberately engineer negative real rates to stimulate borrowing and spending.
It depends on your purpose. For past analysis, use the published CPI or GDP deflator for the period. For future projections, use your best estimate of expected inflation (e.g., inflation-linked bond breakeven rates or central bank targets). The result is only as accurate as your inflation assumption.
Also known as
TG we-Calculate Editorial Team. (2026). Real Interest Rate Calculator — Fisher Equation [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/real-interest-rate-calculator
TG we-Calculate Editorial Team. "Real Interest Rate Calculator — Fisher Equation." TG we-Calculate. 2026. https://we-calculate.com/calculator/real-interest-rate-calculator.
TG we-Calculate Editorial Team, "Real Interest Rate Calculator — Fisher Equation," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/real-interest-rate-calculator
@misc{wecalculate_real_interest_rate_calculator, title = {Real Interest Rate Calculator — Fisher Equation}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/real-interest-rate-calculator}}, year = {2026}, note = {TG we-Calculate} }
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