Nominal vs. real return: what inflation does to your results

Every return you see quoted — on a fund factsheet, a savings account, a bond, a property — is almost always a nominal return: how much the number of units of money grew. What you actually care about is what that money can buy. That is the real return, and the gap between the two is inflation.

The difference in one example

Say an investment returns 7% in a year when prices rise 3%. Your balance is 7% bigger, but everything you might spend it on is 3% more expensive. Your purchasing power has grown by roughly 4%, not 7%. That roughly-4% is the real return.

Over long periods the difference becomes enormous. $10,000 growing at 7% for 30 years becomes about $76,000. Growing at a real 3.9% — the same investment measured in purchasing power — it becomes about $31,000 of today’s money. Both numbers are correct; only one tells you what you will be able to buy.

The exact formula

Subtracting inflation from the nominal return is a good mental shortcut, but it slightly overstates the real return. The precise version, known as the Fisher equation, divides instead of subtracting: real return = (1 + nominal return) ÷ (1 + inflation) − 1.

With a 7% nominal return and 3% inflation, that gives 1.07 ÷ 1.03 − 1 ≈ 3.88%, a little below the 4% shortcut. At low rates the two methods are close; at high rates of inflation the shortcut can be noticeably wrong, so it is worth using the exact version for anything you plan with.

Fees and taxes come off first

Inflation is not the only thing standing between the headline return and your purchasing power. Fees are taken from the nominal return before inflation does its work. A 7% return with a 1% annual fee is really 6%, and after 3% inflation the real return falls to about 2.9% — roughly a quarter less than the fee-free 3.9%.

Taxes work the same way, and they bite harder than they look because they are charged on the nominal gain, including the part that only kept up with inflation. A savings account paying 5%, taxed at 25%, leaves 3.75% after tax. With 3% inflation, the real after-tax return is about 0.7% — positive, but barely.

When a positive return is really a loss

Whenever the nominal return is lower than inflation, the real return is negative: your balance grows, but it buys less every year. Cash left in an account paying 1% while prices rise 3% loses about 2% of its purchasing power each year. Over a decade, that quietly removes almost a fifth of what the money can buy.

This is why “safe” is not the same as “risk-free”. Cash protects you from market falls, but not from inflation. Over long horizons, the main risk for very cautious savers is often a steady loss of purchasing power rather than a sudden crash.

Thinking in today’s money

The most useful habit is to convert long-term projections back into today’s purchasing power. At 3% inflation, $10,000 in ten years will buy what about $7,400 buys today, and $100,000 in thirty years will buy what about $41,000 buys today.

A retirement target of “one million” sounds the same in every decade, but it is worth far less in thirty years than it is now. Plan in today’s money and the targets stay meaningful; plan in future money and inflation quietly moves the goalposts.

Which inflation rate should you assume?

Nobody knows future inflation. Many central banks aim for around 2% a year, but actual inflation has often been higher or lower for years at a time, and your own cost of living may rise faster or slower than the official average depending on what you spend money on. A sensible approach is to test a range — say 2%, 3%, and 4% — and see how much the conclusion depends on it.

Convert any nominal return into a real one, with fees, in the real return calculator, and see what a sum of money will be worth in the future with the inflation calculator. For the growth side of the story, read compound interest explained.