Average Return Calculator · Practical guide
What Does Standard Deviation of Returns Mean?
It is the volatility number next to your average return — how widely individual years scatter around the mean.
At a glance
The Short Answer
Standard deviation measures how far individual annual returns typically sit from their average. A series averaging 6% with a standard deviation of 4.6% has most years landing roughly between 1.4% and 10.6%. Higher standard deviation means a bumpier ride — more risk for the same average.
Interactive tool
Average Return Calculator
Enter your own values, then compare the result with the examples below.
Results
A Concrete Reading
Take the returns 8%, −2%, 12%, 5%, 7%. The average is 6.00% and the calculator above reports a standard deviation of 4.60%. By the common rule of thumb, about two-thirds of years fall within one standard deviation of the mean (1.4% to 10.6%), and about 95% within two (−3.2% to 15.2%). The −2% year fits comfortably inside that band.
Same Average, Different Risk
| Return Series | Average | Std Deviation | Feel |
|---|---|---|---|
| 6, 6, 6, 6, 6 | 6.00% | 0.00% | Perfectly steady |
| 8, −2, 12, 5, 7 | 6.00% | 4.60% | Mildly bumpy |
| 25, −15, 20, −10, 10 | 6.00% | 15.94% | Volatile |
All three average 6% a year arithmetically, but the volatile series compounds to less: its geometric average is about 4.77%, versus 5.90% for the mild series. Volatility is the tax you pay on the way to your average.
How to Use the Number
Compare standard deviations across investments with similar averages to see which takes the smoother path, and size your expectations: a portfolio with a 15% standard deviation can plausibly deliver a double-digit loss in any given year even with a healthy long-term average. Enter any return series above to get its average, volatility, and compounded result together.
Frequently Asked Questions
What is a typical standard deviation for stock market returns?
Broad US stock indexes have historically shown annual standard deviations around 15-20%, while high-quality bond portfolios often run in the low single digits.
Is a high standard deviation always bad?
Not necessarily — it means wider swings in both directions. It becomes a problem when the swings exceed what you can tolerate without selling at the wrong time.
How does volatility lower my compounded return?
Losses need larger gains to recover, so volatility drags the geometric average below the arithmetic one. The gap is roughly half the variance of returns.
Does this calculator use population or sample standard deviation?
It divides by n (population standard deviation), treating the entered years as the complete set of returns you want to describe.