The Average That Lies
Here's the classic trap. An investment gains 50% one year and loses 50% the next. Average return: (50 − 50) ÷ 2 = 0%. Actual outcome: $10,000 → $15,000 → $7,500. You're down 25% while the "average" says you broke even.
The arithmetic average overstates performance whenever returns vary — and returns always vary. The gap even has a name (volatility drag), and it's why every serious performance figure you see quoted, from index funds to hedge funds, uses CAGR instead.
CAGR: The Honest Number
The Compound Annual Growth Rate answers one question: what steady annual rate would have turned my starting value into my ending value over this period?
CAGR = (Ending value ÷ Beginning value)^(1/years) − 1
A portfolio that grew from $10,000 to $18,000 over 6 years has a CAGR of (1.8)^(1/6) − 1 ≈ 10.3% — regardless of whether the ride was smooth or wild. CAGR compresses the whole journey into the one number that compounding actually delivered.
A milder example of the average-vs-CAGR gap: gain 30%, then lose 10%. Average: 10%. CAGR: √(1.30 × 0.90) − 1 ≈ 8.2%. The gap grows with volatility — which is exactly why volatile investments love to advertise their average.
Total Return vs Annualized Return
"My investment is up 60%!" means little without the time axis:
- 60% over 5 years → CAGR ≈ 9.9% — solid
- 60% over 15 years → CAGR ≈ 3.2% — barely ahead of inflation
Total return is for bragging; annualized return is for decisions. Only annualized figures can be compared across investments held for different lengths of time — which is nearly always the comparison you actually want to make.
Three Mistakes That Skew Your Number
1. Forgetting dividends. Price charts ignore distributions, and dividends have historically contributed a large share of total stock market returns. Always measure total return: ending value including reinvested dividends.
2. Ignoring your contributions. If you added money along the way, simple CAGR overstates your skill — some of that "growth" was just deposits. For accounts with ongoing contributions, your brokerage's money-weighted or time-weighted return figures handle this correctly; simple CAGR fits lump-sum investments best.
3. Skipping the benchmark. A 12% CAGR sounds great — unless a plain index fund did 14% over the same period with less effort. Judging performance means comparing against what doing nothing would have earned. Consistently matching a cheap index is a genuinely good outcome; consistently beating it is rare.
What Counts as a Good Return?
For calibration, over the long run: U.S. stocks have averaged roughly 10% nominal (about 7% after inflation), bonds meaningfully less, and cash barely keeps pace with inflation. Any pitch quoting reliable returns far above these deserves deep suspicion — and after fees and taxes, the return you keep is the only one that compounds for you. A 1% annual fee on a 7% return isn't "1% less"; over 30 years it consumes roughly a quarter of the final portfolio.
Key Takeaway
Measure investments by CAGR on total return (dividends included), over a stated period, against a benchmark — and be suspicious of any "average return" from a volatile asset. Compute your own holdings' CAGR from just three inputs: what you started with, what it's worth now, and how long it took.