Inflation Impact on Investments

Real vs Nominal Returns

Nominal return is the percentage shown on your brokerage statement. Real return is what remains after subtracting inflation. At 8% nominal return and 3% inflation, real return calculates to approximately 4.85% (not simply 5%).

The Fisher Equation

Real Rate ≈ Nominal Rate − Inflation Rate. More precisely: (1 + real) = (1 + nominal)/(1 + inflation).

Why This Gap Compounds Over Time

The difference between nominal and real returns appears small in year one. Over decades, it compounds into a significant gap. A pot that looks impressive on paper represents less purchasing power than expected. Inflation functions as a quiet annual charge on future wealth. Longer time horizons amplify this effect in long-term financial planning.

Patterns People Observe

A frequent pattern: planning around nominal figures alone. A projected balance doubling over twenty years appears encouraging. If inflation has run at 3% throughout, that figure buys considerably less than it appears. Inflation rates also change over time. Using a single fixed rate is a simplification—which is what this tool illustrates. Results function as illustrations rather than precise forecasts. Exploring a range of inflation assumptions reveals the pattern across scenarios.

Quick example

With investment amount of 10,000 and nominal annual return of 8 (plus annual inflation of 3 and years of 20), the result is 25,806.59. Change any figure and watch the output shift — the pattern often proves more useful than memorizing the formula.

Which inputs matter most

You enter Investment Amount, Nominal Annual Return, Annual Inflation, and Years. Rate and time horizon typically dominate — compounding means a small change in either reshapes the final figure more than a similar shift in contribution size. Testing by doubling one input at a time illustrates this relationship.

What's happening under the hood

This calculator applies the Fisher equation to adjust nominal investment returns for inflation's eroding effect. It compounds the initial investment at the nominal rate, then divides by inflation compounding to show real purchasing power. Results assume constant annual rates with no fees or taxes—actual outcomes vary based on market conditions and individual circumstances. The formula appears in full below. If the number appears off, you can retrace the calculation by hand — that's the purpose of showing the working.

Why investors run this

Intuition for compounding typically diverges from reality — not because the math is difficult, but because linear thinking doesn't account for curves. Running numbers through a calculator like this one recalibrates intuition before decisions about contribution rate, asset mix, or retirement age.

What this doesn't capture

Steady-rate math ignores real-world volatility. Actual returns are lumpy; sequence-of-returns risk matters most in drawdown; fees and taxes drag on compound growth; and behaviour in drawdowns can reduce outcomes below the projection. The number represents one scenario rather than a forecast.