Inflation — nominal vs. real return

The slow tax that eats your money

Inflation is the rate at which the general price level rises. ₩100 buys less bread next year than this year. The bread didn't change; the money did.

For investors, inflation is one of the most important silent forces:

• It eats into nominal returns to give real returns (last lesson's r_real ≈ r_nominal − π).
• It distorts comparisons across time periods. A 5% return in 1980 (when inflation was 13%) was a disaster; a 5% return in 2020 (when inflation was 1%) was great.
• It interacts with central bank policy in ways that ripple through every asset class.

Where inflation comes from (briefly)

Two textbook causes that often co-occur:

Demand-pull: Too much money chasing too few goods. When demand exceeds supply, sellers raise prices. Stimulus-driven inflation, post-pandemic 2021-2022 reopening, etc.

Cost-push: Input costs rise (oil, wages, raw materials), and producers pass them through. 1970s OPEC oil shocks, supply-chain disruptions in 2021, etc.

Real economies rarely have just one cause. Modern inflation is usually a mix, with feedback loops (wage-price spirals, expectations becoming self-fulfilling). Central banks try to manage inflation toward a target (typically 2% in developed economies).

How inflation is measured

The most-cited measure is the Consumer Price Index (CPI) — a basket of typical household goods and services, tracked over time. The percent change in CPI from one year ago is the headline inflation rate.

CPI has issues (basket composition lags real consumption changes, hedonic adjustments are debated, etc.), but it's the standard. Other measures: PCE (preferred by the Fed), Core CPI/PCE (excluding food and energy, which are volatile), wholesale price indexes.

Quick sanity checks: when groceries feel more expensive every week, when rent jumps significantly year-over-year, when "value menus" disappear from fast food — those are real-world signs that headline inflation is running hot.

Nominal vs real returns — done right

Approximation from last lesson:

Exact (Fisher equation):

For modest values (single-digit percent), the approximation is fine. For high inflation (Argentina, Turkey, 1970s US), the gap matters. Always do the exact calculation when inflation is high.

Stocks have historically been a decent inflation hedge over long horizons (companies can usually raise prices to keep pace). Bonds, especially long-term fixed-rate bonds, are inflation-vulnerable — your fixed coupon doesn't keep up. TIPS (Treasury Inflation-Protected Securities) and similar instruments adjust principal with CPI, so they protect real value.

The investor's takeaway: think real, report nominal

When you compute long-term returns, retirement projections, or compare across decades, do the math in real terms. A "7% nominal return" in a 5% inflation environment is a 2% real return. Headlines lie about long-term performance unless they specify real or nominal.

When you're benchmarking last year's return against goals, nominal is fine — inflation in any single year is roughly known and small adjustments are usually OK. Long horizons are where nominal vs. real really matters.

The takeaway

Inflation = rate of price-level increase. Eats into nominal returns. Real return ≈ nominal − inflation (or use Fisher equation precisely). Comes from demand-pull and cost-push, often together. Measured by CPI / PCE. Stocks tend to keep up over long horizons; fixed-rate bonds don't. When comparing performance across time, especially long horizons, always think in real terms.