Inflation and Real Returns

Your real return is what your money earns after subtracting inflation’s erosion of purchasing power — and it’s the number that determines what you can actually buy. A 7% return during 3% inflation isn’t really 7%, and it isn’t quite the “7 minus 3 = 4%” of quick mental math either: the true figure is 3.88%, and over decades that distinction compounds into serious money.

What’s the difference between nominal and real returns?

A nominal return counts dollars; a real return counts what those dollars can buy. If your portfolio grows 7% in a year when prices rise 3%, you have 7% more dollars but each one buys less. Nominal returns are what banks advertise, statements report, and this site’s calculators display. Real returns are what fund your actual life — groceries, rent, retirement — which is why long-range planning that ignores inflation quietly overpromises.

The Fisher equation

The exact relationship between nominal returns, inflation, and real returns is the Fisher equation:

$1 + r_{\text{real}} = \frac{1 + r_{\text{nominal}}}{1 + i}$

Dividing rather than subtracting matters because inflation doesn’t just eat your gains — it also erodes the principal those gains are measured against. For 7% nominal and 3% inflation, the Fisher equation gives 3.88% rather than the 4% shortcut. The error looks small in a single year, but the shortcut always flatters the result, and compounding amplifies flattery: over 30 years, planning around 4% instead of 3.88% overstates your ending purchasing power by several percent.

The subtraction shortcut is fine for conversation. Use the real thing for planning — the inflation calculator applies the Fisher equation for you.

What inflation does over 30 years

Inflation’s damage is invisible year to year and dramatic across decades. At 3%, prices roughly double in 24 years (the Rule of 72 working against you). Three concrete versions of the same fact:

• Uninvested cash: $10,000 left under the mattress for 30 years of 3% inflation buys what $4,119.87 buys today — less than half its face value.
• An invested portfolio: $10,000 at 7% compounded monthly grows to $81,164.97 in 30 years — but in today’s purchasing power, that’s $33,438.89. Still excellent growth. Just not eight-fold growth in any sense your grocery bill recognizes.
• A retirement target: if “$1 million” is your number, remember it’s today’s million you mean. At 3% inflation, hitting the same purchasing power in 30 years requires about $2.4 million nominal.

The pattern in all three: inflation never shows up as a loss on any statement, which is exactly what makes it easy to ignore and expensive to forget.

Are nominal projections wrong?

No — nominal projections answer a different question, and this site’s calculators are deliberately nominal. “How many dollars will I have?” is the right question for comparing scenarios, setting contribution amounts, and understanding compounding mechanics, because inflation affects every scenario you compare more or less equally. The main calculator, savings, and retirement tools all show nominal values and say so.

“What will it buy?” is the second question, and the honest workflow is to ask it separately: project nominally, then run the result through the inflation calculator to translate it into today’s dollars. Keeping the two steps separate keeps both answers interpretable — a lesson learned from every confusing “inflation-adjusted-ish” projection that mixes them.

If you’d rather have the adjustment built into the projection itself, the CompoundFX app includes inflation (and tax) adjustments in its free tier, applied properly and labeled clearly.

Inflation isn’t the only force quietly separating your statement balance from what you keep — taxes create an analogous drag on compounding, and the two effects stack.

Three rules of thumb worth keeping

For everyday planning, three heuristics cover most of what the Fisher equation has to say:

1. Divide 72 by the inflation rate to know how fast prices double — at 3%, your cash halves in buying power every ~24 years, which is the strongest argument against holding long-term savings in cash.
2. Subtract, then shave a little. Nominal minus inflation is close; the true Fisher result is always slightly lower, and the gap widens as either rate rises. For 7% and 3%, subtracting says 4%; the truth is 3.88%.
3. State long-term goals in today’s dollars, then inflate the target — not the other way around. “Enough to spend $40,000 a year in today’s money” is a plannable goal; “$1 million someday” quietly shrinks every year you wait.

The takeaway

Think in pairs: every nominal number deserves a real twin. A 7% return is 3.88% real at 3% inflation; a 30-year nominal balance of $81,164.97 is $33,438.89 of today’s purchasing power; a million-dollar goal is a two-point-four-million-dollar goal a generation from now. None of this diminishes compounding — real growth is still growth, and equities have historically outrun inflation by a wide margin over long horizons. It just keeps your plan denominated in the only currency that ultimately matters: what your money can do for you.