6.12: The Real and Nominal Interest Rate

When you put money into a savings account or take out a loan, you usually see an interest rate. This number is called the nominal interest rate. It shows how much extra money you’ll earn or owe over time. But it doesn’t tell the full story. If prices go up while your money is sitting in the bank, you might not be gaining as much as you think. That’s where the real interest rate matters.

The real interest rate takes inflation into account. Inflation means things cost more than they used to, so your money buys less. To find out how much you’re really gaining, subtract the inflation rate from the nominal interest rate.

Say someone puts $6,000 into a savings account that pays 4% interest. At the end of the year, the account grows to $6,240. But if inflation that year was 3%, everyday prices have also gone up. That extra $240 won’t stretch as far. In reality, the person’s money only grew in value by about 1%.

Now imagine the interest rate stays the same, but inflation rises to 5%. Even though the bank pays interest, the value of the money actually shrinks. The account balance is higher, but what it can buy is less than before.

This idea helps explain why just looking at your balance isn’t enough. Real interest rates give a clearer picture of what’s really happening with your money. If you want your savings to grow in a way that actually helps you in the future, it’s important to understand how inflation fits into the equation. Even a small change in inflation can make a big difference in what you gain or lose over time.

A small business owner, John, transfers ten thousand dollars from his earnings into a savings account. The bank offers a three percent annual interest rate, so his balance grows to ten thousand three hundred dollars after one year.

At first glance, it seems John earned three hundred dollars. This amount results from the nominal interest rate of three percent—the return before adjusting for inflation.

But during that same year, inflation reached 2%. Something that cost one hundred dollars now costs one hundred and two, showing how each dollar buys a little less.

Economists use a simple formula to find the real interest rate, a better indicator of actual earnings. The real interest rate is equal to the nominal interest rate minus the inflation rate, which measures the real gain. In John’s case, the real rate is one percent.

So, while his account balance increased by three percent, his real gain in purchasing power was only one percent, reflecting what his money could actually buy.

Now imagine if inflation rose to four percent. Despite the higher balance, John would face a negative real interest rate of minus one percent, meaning his money would lose value in real terms.

Understanding real interest rates is key to measuring actual financial growth.