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Real vs. Nominal Returns
Why inflation changes what your portfolio growth actually means
When your investment account shows a 10% gain, that's your nominal return — the raw number before adjusting for inflation. Your real return is what matters: the increase in your actual purchasing power. If inflation was 3%, your real return was approximately 7%. The difference between these two numbers is the single most common source of confusion in retirement planning.
It sounds like a technical distinction, but it has enormous practical consequences. A retirement plan built on nominal returns will systematically overestimate what your money can buy. A plan built on real returns — as Calcifir is — keeps the math honest by measuring everything in today's dollars from start to finish.
The Fisher equation
The relationship between real and nominal returns is described by the Fisher equation, named after economist Irving Fisher. The simplified approximation works well for low inflation rates. The precise version is needed when inflation is high.
Approximation
real ≈ nominal − inflation
7% ≈ 10% − 3%
Precise (Fisher)
1 + real = (1 + nom) ÷ (1 + inf)
1.068 = 1.10 ÷ 1.03
At the 3% long-run average inflation rate, the approximation is close enough for practical planning. At 8%+ inflation (as in the 1970s), the gap between the two formulas becomes meaningful and the precise version matters more.
What history actually shows
Based on roughly 150 years of US market data, the standard reference points for long-run returns are well-established. These historical averages underlie most FIRE planning; Calcifir itself plans on a more conservative 5% real return by default (see below).
| Asset class | Nominal | Inflation | Real |
|---|---|---|---|
| US stocks (S&P 500) | ~10% | ~3% | ~7% |
| US bonds (intermediate) | ~4% | ~3% | ~1% |
| Inflation (CPI) | — | ~3% | — |
Long-run historical averages. Individual decades vary significantly. International returns differ from US. Past performance does not guarantee future results.
Why Calcifir defaults to a conservative 5% real
The ~7% real figure above is the long-run historical average for US equities after inflation — not a guarantee, and specific decades can be much worse (the 2000s produced near-zero real returns) or much better. Calcifir defaults to a more conservative 5% real return instead: most plans aren't 100% equities, and a lower assumption produces a higher FIRE number and a longer timeline — a margin of safety many savers prefer (the periods behind the Trinity Study's 4% rule included far worse stretches). You can change it in your plan's assumptions.
The illusion of nominal growth
The chart below shows three lines — for a $500K starting portfolio over 30 years. A high nominal return sounds much better than a 7% real benchmark, but when you strip out inflation from the nominal return, the gap shrinks dramatically. The relevant number is always the real one. Drag the sliders to see how a chosen nominal return and inflation rate translate into real growth.
Explore: What if...
Real return (Fisher)
6.8%
6.8% = (1 + 10%) ÷ (1 + 3%) − 1
A 10% nominal return loses 3.2% to inflation — that gap is the illusion.
$500K portfolio growth — in today's dollars
A 10% nominal return adjusted for 3% inflation to show real purchasing power
After 30 years: 7% real benchmark → $3.81M · 10% nominal as real (6.8%) → $3.59M · 10% nominal un-adjusted → $8.72M. Only the real figure tells you what you can actually spend.
Why Calcifir works in real terms
FIRE planning has two sides: your expenses and your portfolio growth. Calcifir models your retirement expenses in today's dollars — your $60K/yr spending goal is $60K in today's purchasing power, not a number that inflates over time. To keep both sides of the equation consistent, the growth rate must also be in today's dollars. That means using real return, not nominal.
The consistency principle
If you model expenses in today's dollars but grow your portfolio at a nominal rate, your model contains a hidden assumption: that your expenses will grow with inflation while your portfolio growth is measured before inflation. This produces wildly optimistic projections — effectively double-counting inflation as a tailwind. Using real returns throughout keeps the math internally consistent.
The practical difference
At 10% nominal and 7% real, a $500K portfolio becomes approximately $8.7M nominal after 30 years — but only $3.8M in today's dollars. That's the number that tells you what you can actually spend. FIRE calculators that use nominal returns need to also apply a separate inflation adjustment to retirement spending each year. The real-return approach builds this in from the start.
Sequence of real returns matters
Even if average real returns are identical, the order in which they occur dramatically affects retirement outcomes. Two retirees with the same 7% average real return over 30 years can have very different results if one experiences large early losses while the other experiences them late. This is sequence-of-returns risk, and it affects real returns exactly as much as nominal ones.
Learn about sequence-of-returns risk →Example return assumptions
Example growth rateExample
Real return
5%
after inflation, in today's dollars
Implied nominal
8.2%
assuming 3% long-run inflation
This example household plans on a 5% real return — the growth in purchasing power after inflation. At 3% inflation that implies a nominal return of about 8.2%. The historical long-run average for US equities is closer to ~7% real (~10% nominal); planning on a lower real figure produces a higher FIRE number and a longer timeline, which some savers prefer as a margin of safety. Use the explorer above to see how any real return follows from a nominal return and an inflation rate.
What an account shows vs. what Calcifir uses: When the market is up 10% in a year, an account balance grows 10% nominally. Calcifir plans in real returns — the growth in purchasing power — so every projection is already expressed in today's dollars.
Example figures from a sample household. Build your plan →
Common mistakes
Using a nominal rate with inflation-adjusted expenses
If you enter 10% as your return assumption but model your retirement spending as a fixed dollar amount (not growing with inflation), you've accidentally mixed nominal and real. The model will be far too optimistic — effectively assuming your spending stays flat in nominal terms while your portfolio compounds at full nominal rate.
Confusing account value with purchasing power
$1M growing at 10%/yr for 30 years becomes $17.4M. At 3% inflation, that $17.4M buys only what $7.2M buys today. People who plan around nominal millionaire milestones often underestimate how much inflation erodes the real value of a given dollar target.
Treating the 7% real as a guaranteed floor
The 7% real return is a long-run historical average, not a minimum. The 2000s produced near-zero real returns for a full decade. Japan's market went 30+ years with negative real returns. A robust FIRE plan stress-tests at 4–5% real to understand what happens when the long-run average doesn't apply to your specific retirement window.
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