Fisher Effect Calculator
Enter the nominal interest rate and the expected inflation rate to see the real interest rate under the Fisher effect.
Updated
Fisher Effect Calculator
Our Fisher Effect Calculator turns a nominal interest rate and an expected inflation rate into a real interest rate, the return that is left once rising prices are taken into account. Type the two rates as percentages. It returns the real rate from the simplified Fisher formula, and next to it the exact Fisher rate so you can see how close the shortcut is. It is useful for economics and finance students, savers and borrowers comparing offers, and analysts reading interest rates across countries.
Quick answer
Under the Fisher effect, the real rate = nominal rate − expected inflation: with a nominal rate of 7% and expected inflation of 3%, 7% − 3% = 4%.
- Nominal rate: the quoted interest rate, before inflation.
- Expected inflation: how fast prices are expected to rise over the same period.
- Real rate: the gain in buying power, nominal rate − expected inflation.
- Fisher effect: when expected inflation rises by 1 point, the nominal rate rises by 1 point too.
What Is the Fisher Effect?
The Fisher effect is the idea that nominal interest rates move one-for-one with expected inflation, so that the real interest rate stays roughly steady. It is named after the American economist Irving Fisher, who set it out in the early twentieth century.
The reasoning is simple. Lenders care about what their money will buy when it is repaid. If they expect prices to rise by 3% a year, they ask for 3 points more interest to make up for it. Borrowers accept, because they expect to repay in money that is worth less. The inflation forecast is passed straight into the nominal rate.
Fisher Effect Formula
- r: the real interest rate.
- i: the nominal interest rate.
- π: the expected inflation rate.
Rearranged, the same formula shows how a nominal rate is built up:
A nominal rate is the real return lenders want plus the inflation they expect. All three rates must cover the same period, usually a year.
How to Calculate the Real Rate
A bond pays a nominal rate of 7% a year and inflation is expected to be 3% a year:
= 4%
- Take the nominal rate. 7%.
- Subtract expected inflation. 7 − 3 = 4.
- Read the real rate. 4% a year.
The real interest rate is 4%. The exact Fisher rate for the same inputs is about 3.8835%, so the shortcut is out by roughly 0.12 of a point.
The Fisher Effect in One Picture
The shaded block is the real rate and the outlined block is expected inflation. The number on top is the nominal rate, the two stacked together.
| Expected inflation | Nominal rate |
|---|---|
| 1% | 3% |
| 3% | 5% |
| 6% | 8% |
| 10% | 12% |
Simplified vs Exact Fisher Formula
Subtracting the two rates is a shortcut. The exact relationship divides instead of subtracting:
The shortcut is close when rates are low and drifts as they rise:
| i and π | Simple | Exact |
|---|---|---|
| 7%, 3% | 4% | 3.8835% |
| 15%, 10% | 5% | 4.5455% |
| 60%, 50% | 10% | 6.6667% |
This calculator shows the simple result as the main answer and the exact rate in the row below it. For a page built around the exact formula, see our Fisher Equation Calculator.
Fisher Effect Examples
A savings account. The account pays 4.5% and inflation is expected to be 3.2%:
= 1.3%
A negative real rate. A deposit pays 1.5% while inflation is expected to be 4%:
= −2.5%
The balance grows, but what it can buy shrinks by about 2.5% a year.
Falling prices. The nominal rate is 2% and prices are expected to fall by 1%, so enter −1 for inflation:
= 3%
With deflation, the real rate is higher than the nominal rate.
Expected vs Actual Inflation
The Fisher effect is about the inflation people expect when a loan is agreed. What happens afterwards can be different.
- Before the fact (ex ante): nominal rate − expected inflation. This is the real rate both sides planned for.
- After the fact (ex post): nominal rate − actual inflation. This is the real rate that was earned.
- Inflation higher than expected: borrowers gain, because they repay in cheaper money.
- Inflation lower than expected: lenders gain, because the money repaid buys more.
Enter expected inflation to plan ahead, or the actual inflation figure to look back at a past period.
The International Fisher Effect
The same idea is applied across countries. If real rates are similar everywhere, a country with a higher nominal rate must have higher expected inflation, and its currency is expected to lose value by about the gap between the two nominal rates.
For example, if one country has a nominal rate of 6% and another has 2%, the international Fisher effect predicts that the first currency will weaken by roughly 6 − 2 = 4% a year against the second. It is a long-run tendency, not a forecast for any given month. Our Currency Forward Calculator prices the related interest rate gap into a forward exchange rate.
Does the Fisher Effect Hold in Practice?
- Long run. Over many years, countries with higher inflation do tend to have higher nominal rates.
- Short run. Central banks set short-term rates, and expectations adjust slowly, so the one-for-one link is loose.
- Unobserved input. Expected inflation cannot be measured directly. It is estimated from surveys or from bond prices.
- Rates near zero. When nominal rates cannot fall much further, a drop in expected inflation raises the real rate instead.
- Taxes. Interest is usually taxed on the nominal amount, so the after-tax real rate is lower than the result here.
The result is for education and planning and is not financial advice.
Key Terms
- Nominal rate
- The quoted interest rate, not adjusted for inflation.
- Real rate
- The interest rate after taking inflation off.
- Expected inflation
- The rise in prices people expect over the life of a loan.
- Fisher effect
- Nominal rates rising one-for-one with expected inflation.
- Fisher equation
- The exact link: 1 + i = (1 + r) × (1 + π).
- Deflation
- Falling prices, entered here as a negative inflation rate.
How to Use the Fisher Effect Calculator
- Enter the nominal interest rate. Type the quoted interest rate as a percentage, such as 7.
- Enter expected inflation. Type the expected inflation rate for the same period, such as 3. Use a minus sign for deflation.
- Read and copy the result. The real interest rate appears as you type, with the working and the exact Fisher rate for comparison. Press Copy to copy it, or Clear or Esc to start again.
Example: a savings rate of 4.5% with expected inflation of 3.2% gives a real interest rate of 1.3%.
Who Can Use This Calculator?
Frequently Asked Questions (FAQs)
What is the Fisher effect?
It is the theory that nominal interest rates rise and fall one-for-one with expected inflation, which leaves the real interest rate roughly unchanged.
What is the Fisher effect formula?
Real interest rate = nominal interest rate − expected inflation. Rearranged, nominal interest rate = real interest rate + expected inflation.
What is the real interest rate if the nominal rate is 7% and inflation is 3%?
It is 4%, because 7% − 3% = 4%. The exact Fisher rate for the same inputs is about 3.8835%.
Can the real interest rate be negative?
Yes. When expected inflation is higher than the nominal rate, the real rate is negative and money saved loses buying power even though the balance grows.
How accurate is the simplified Fisher formula?
It is very close at low rates. At 7% and 3% it is out by about 0.12 of a point. At high rates the gap grows, so use the exact rate shown in the results.
What is the difference between the Fisher effect and the Fisher equation?
The Fisher equation is the formula that links nominal rates, real rates and inflation. The Fisher effect is the prediction drawn from it: nominal rates follow expected inflation.
What is the international Fisher effect?
It extends the idea to exchange rates. The currency of the country with the higher nominal interest rate is expected to weaken by about the difference between the two rates.
Who was Irving Fisher?
Irving Fisher was an American economist who worked on interest, capital and money. The Fisher effect and the Fisher equation are both named after him.
Is the Fisher Effect Calculator free?
Yes. It is free to use, with no sign-up and no limit on how many times you use it.
Sources
- Wikipedia. Fisher effect.
- Corporate Finance Institute. Fisher Effect.
- Wikipedia. Fisher equation.
- Wikipedia. International Fisher effect.
- Wikipedia. Real interest rate.
- Econlib. Irving Fisher.
- Econlib. Interest Rates.
Try our Fisher Effect Calculator to see what an interest rate is really worth after inflation.