- Nominal amounts are measured in current money.
- Real amounts adjust for price changes.
- Subtracting inflation is an approximation for small rates.
Nominal growth describes the change in a money amount. Real growth describes how its purchasing power changes after accounting for inflation.
Separate balances from buying power
A balance can rise while the goods and services it could buy rise faster in price. Neither number is inherently wrong; they answer different questions. Nominal values are useful for account statements and payments. Real values help compare purchasing power over time.
The calculation
For a simplified one-period illustration, the real growth rate is (1 + nominal growth) divided by (1 + inflation), minus one. Rates are written as decimals. With hypothetical nominal growth of 5% and inflation of 3%, the real rate is approximately 1.94%, not exactly 2%.
Subtracting inflation is a convenient approximation when the rates are modest. The division formula explains why it becomes less accurate for larger numbers.
Your price basket may differ
An inflation measure summarizes a basket of prices. It does not predict how every household’s costs change. Rent, childcare, transport, or health expenses can move differently from a broad index.
Use the right label
Our compound-interest calculator produces nominal outcomes. Its future balance is not adjusted for inflation, tax, or fees. When comparing scenarios, keep the time period and inflation assumption consistent.
Do not interpret a steady nominal return assumption as a promise of steady real purchasing power. Both the return and the price level can change.
Check a pay rise against the same-period basket
Suppose nominal income rises 3% and the price of a fixed basket rises 5% over the same period. These are hypothetical assumptions, not current inflation or wage data. The real income change is 1.03 / 1.05 − 1 = approximately −1.90%. A larger nominal income buys less of that basket. Subtracting 5% from 3% gives −2%, a useful approximation but not the exact result.
Keep the quantities comparable. Buying extra goods is a change in consumption as well as spending; a larger total alone does not measure inflation. Your basket can differ from a national consumer price index.
An unchanged balance has a different result
If prices rise 5% and a cash balance earns no interest, its real change is 1 / 1.05 − 1 = approximately −4.76%. A 5% price increase is not an exact 5% purchasing-power loss, because one multiplies by the price factor and the other divides by it.
For a saving account, use the nominal return after relevant costs and taxes rather than assuming every cash balance has zero return. A foreign-currency balance adds exchange-rate exposure relative to the currency of your future bills.
Use the calculation after an energy shock
A higher diesel price can affect some delivery and production costs. That does not tell you your personal inflation rate. First establish the actual change in your basket; then compare it with income growth for the same period. An oil shock alone cannot determine the result of this formula.
Follow the mechanism in oil conflicts and the cost of living and distinguish crude from finished fuel in why diesel can stay expensive. Explore the purchasing-power calculator or salary calculator using assumptions appropriate to your own period.
A calculation is not an investment instruction
Finding a negative real income change describes a budget problem. It does not establish which asset will perform best next. Keep access to near-term bill money in view and examine market, currency and concentration risk before assuming a higher return will compensate for the loss. Read diversification for how different holdings can still share exposures.