For things that compound — growth rates, returns, ratios — the plain average overstates. The geometric mean multiplies the values and takes the n-th root, giving the true average rate that reproduces the total compounding.
The example
Yearly growth factors; the geometric mean is the true average rate.
| A | B | |
|---|---|---|
| 1 | Year | Factor |
| 2 | 2023 | 1.20 (+20%) |
| 3 | 2024 | 0.90 (−10%) |
| 4 | 2025 | 1.15 (+15%) |
| 5 | Geo mean | 1.073 (+7.3%) |
The formula
The average compounding factor, then the rate:
How it works
The geometric mean respects compounding:
- It multiplies all the values together, then takes the n-th root (n = how many values).
- For growth, feed it the factors — 1.20 for +20%, 0.90 for −10% — not the raw percentages.
- The result is the single factor that, compounded each period, gives the same end result. Subtract 1 for the average rate.
- It’s always ≤ the arithmetic mean, and the gap grows with volatility — which is exactly why it’s the honest measure for returns.
Same as CAGR: the geometric mean of the yearly factors equals the compound annual growth rate. If you only have start and end values, =(end/start)^(1/years)-1 gives the same number without listing each factor.
Try it: interactive demo
Enter yearly % changes, one per line.
Variations
Average growth rate
Subtract 1 from the mean factor:
From start & end (CAGR)
No per-year factors needed:
Manual n-th root
Same as GEOMEAN:
Pitfalls & errors
No zero or negative values. GEOMEAN needs all-positive inputs. Use growth factors (1 + rate), which stay positive even when a rate is negative.
Don’t feed it raw percentages. Averaging 20, −10, 15 directly is the arithmetic mean. Convert to factors (1.20, 0.90, 1.15) first.
Lower than the arithmetic mean. That’s correct, not a bug — volatility makes compounding underperform the simple average.
Practice workbook
Frequently asked questions
How do I calculate the geometric mean in Excel?
Why use geometric mean instead of average for growth rates?
Is the geometric mean the same as CAGR?
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