What is the difference between nominal and real interest rates?
The nominal rate is the rate you are quoted: the APY on a savings account or the rate on a CD or bond. It tells you how many more dollars you will have.
The real rate adjusts for inflation. It tells you how much more you can buy with those dollars. If your account pays 4% and prices rise 4%, you have more dollars at the end of the year, but they buy exactly what your starting balance bought.
How do you calculate the real interest rate?
The exact relationship, sometimes called the Fisher equation, is:
Real rate = (1 + n) ÷ (1 + i) − 1 Approximation: real rate ≈ n − i
Where n is the nominal rate and i is the inflation rate, both as decimals for the same period.
- Suppose your savings earn 4.5% and inflation is 3%.
- Add 1 to each: 1.045 and 1.03.
- Divide: 1.045 ÷ 1.03 ≈ 1.01456.
- Subtract 1: the real rate is about 1.46%.
- The quick estimate gives 4.5% − 3% = 1.5%, which is close enough for most planning.
When is the approximation not good enough?
The shortcut n − i ignores the fact that inflation also eats into the interest itself. At low rates the error is tiny, but it grows as rates rise:
- 4.5% nominal, 3% inflation: exact 1.46%, approximation 1.5%.
- 12% nominal, 10% inflation: exact 1.82%, approximation 2%.
- 25% nominal, 20% inflation: exact 4.17%, approximation 5%.
Use the exact formula when rates are high or when you are compounding over many years, where small differences add up.
Real return at different savings rates and inflation rates
| Savings rate | 2% inflation | 3% inflation | 4% inflation | 6% inflation |
|---|---|---|---|---|
| 0.5% | −1.47% | −2.43% | −3.37% | −5.19% |
| 1% | −0.98% | −1.94% | −2.88% | −4.72% |
| 2% | 0.00% | −0.97% | −1.92% | −3.77% |
| 3% | 0.98% | 0.00% | −0.96% | −2.83% |
| 4% | 1.96% | 0.97% | 0.00% | −1.89% |
| 5% | 2.94% | 1.94% | 0.96% | −0.94% |
| 6% | 3.92% | 2.91% | 1.92% | 0.00% |
Whenever the savings rate is below inflation, the real return is negative, no matter how safe the account is.
What does the real rate mean for your savings?
Take $10,000 earning a hypothetical 4% a year for 20 years while inflation runs at 3%. The balance grows to about $21,911. But prices rise by a factor of about 1.806 over the same period, so in today's money that balance is worth about $12,132. Your buying power grew about 21%, not 119%.
Now take $10,000 at 1% for 10 years with 3% inflation. The real rate is about −1.94%, and the balance buys what about $8,219 buys today, even though it shows more dollars than you deposited.
Taxes make this worse, because tax is charged on the nominal interest. At 4% interest and a hypothetical 22% tax rate, you keep 3.12%. With 3% inflation, the after-tax real return is about 0.12%.
To project a balance, use the savings calculator with your APY, then deflate the result with the inflation calculator to see it in today's dollars.
How does the real rate affect retirement planning?
Retirement goals are usually set in today's money: an income that would cover your current lifestyle. If you project your savings with a nominal return, the result is in future dollars, which will buy less.
One way to keep everything in today's money is to use a real return in your projections. The retirement calculator accepts any return you enter, so you can run it with an expected return minus expected inflation. For a precise figure, convert with the exact formula: 6% nominal with 3% inflation is a real return of about 2.91%, not 3%.
Over decades, small differences compound. The compound interest calculator shows how much a percentage point changes a long-term balance.
What does the real interest rate mean for loans?
Inflation works in a borrower's favor on a fixed-rate loan. Your payments stay the same in dollars while prices and, often, wages rise, so each payment costs you less in real terms. A 6% fixed-rate loan with 3% inflation has a real cost of about 2.91% a year.
The reverse is also true. If inflation falls after you borrow, the real cost of the loan goes up. And variable-rate loans may reset higher when inflation rises, which removes the benefit.
Future inflation is uncertain, so treat any real rate as an estimate. How it applies to you depends on your personal circumstances, and nothing here is financial advice.