What it means
Every interest rate has two parts. There is the real return, the genuine increase in purchasing power a lender expects to earn, and there is compensation for money losing value while it is lent out.
The Fisher effect says the second part tracks expected inflation closely. The distinction between nominal and real matters far more than most people assume.
A savings account paying 6% when inflation runs at 7% is losing you money in real terms, even though the balance on the statement grows every single month. Note the word expected.
The Fisher effect concerns the inflation people anticipate at the moment a rate is agreed, not what actually happens afterwards, so unexpected inflation quietly transfers wealth from lenders to borrowers. There is an international version as well, usually called the international Fisher effect.
It suggests that the currency of a country with higher nominal interest rates should tend to weaken over time, because the rate gap reflects an inflation gap rather than a free return. In practice the relationship is a tendency rather than a law.
Central bank policy, capital controls, the taxation of interest and genuine shifts in the real rate all interfere, so nominal rates and inflation can drift apart for years at a time.
In practice
Real-world examples.
Example
A central bank raises its policy rate from 2% to 6% after inflation expectations jump from 1% to 5%. Savers see a much larger number on their deposit statements but gain nothing in real terms, because the extra interest simply matches the faster erosion of their money.
Example
A pension fund pricing a twenty year bond starts with a 2% required real return and adds a 2.5% long run inflation expectation, arriving at a nominal yield of 1.02 x 1.025 = 4.55%. It will only accept a lower yield if it genuinely believes inflation will run below that level.
Example
An exporter comparing a 12% deposit rate abroad with a 4% rate at home is tempted by the gap. Applying the international Fisher effect, the treasurer treats most of the 8 point difference as expected currency depreciation rather than free profit, and hedges the position accordingly.
Formula
Calculation
Approximation: nominal rate = real rate + expected inflation
Exact form: (1 + nominal rate) = (1 + real rate) x (1 + expected inflation)
Suppose lenders want a real return of 3% and expect inflation of 4%. The approximation gives 3% + 4% = 7%, while the exact calculation gives 1.03 x 1.04 = 1.0712, that is 7.12%.
Test it with cash. A saver puts $100,000 into a one year deposit at 7.12% and ends the year with $107,120. If prices have indeed risen 4%, that sum buys what $107,120 / 1.04 = $103,000 would have bought a year earlier, which is exactly the 3% real return intended.
Now suppose inflation surprises everyone and arrives at 6%. The saver still receives $107,120, but it buys only $107,120 / 1.06 = $101,056.60 in last year's money, a real return of about 1.06% instead of 3%, and the borrower has gained precisely what the saver has lost.Case study
Seen in the real world.
The following is an illustrative and entirely fictional case. Larkfield Mutual, an invented savings institution, promoted a three year fixed deposit at 5% during a period when inflation expectations sat around 2%, presenting savers with an apparent real return of roughly 3%.
Inflation then ran at 6% for two of those three years and 4% in the third. A saver who deposited $50,000 received $50,000 x 1.05 x 1.05 x 1.05 = $57,881.25 at maturity, while the price level rose by 1.06 x 1.06 x 1.04 = 1.1685, meaning the balance needed to reach $58,427.20 simply to stand still. In purchasing power the saver ended with $49,532.79 in year one money, a real loss of $467.21.
In the fictional aftermath Larkfield rebuilt its range around inflation linked deposits and began quoting an expected real return alongside every nominal rate. The lesson was the Fisher effect running in reverse: the institution had locked in a nominal rate that unexpected inflation turned into a real loss for its customers and a cheap source of funding for itself.
Watch out
Common mistakes.
- Judging a savings or loan rate by the headline number without subtracting the inflation expected over the same period.
- Using the simple addition version at large numbers, where the multiplicative form matters; at a 10% real return and 10% inflation the true nominal rate is 21%, not 20%.
- Assuming the Fisher effect describes actual inflation, when it is built on the inflation people expect at the moment the rate is set.
Questions
People also ask.
Does the Fisher effect mean real interest rates never change?
No, it says nominal rates adjust to expected inflation, but real rates still move with savings behaviour, investment demand and central bank policy.
Who gains when inflation turns out higher than expected?
Borrowers, because they repay in money worth less than anticipated, while lenders receive a lower real return than they priced in.
How does tax change the picture?
Tax is charged on nominal interest, so in a high inflation period a saver can pay tax on interest that represents no real gain at all, which makes the after tax real return worse still.
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