Volatility Index Volatility Index
A single number that expresses a slot's volatility. Based on the standard deviation, it shows how widely results can scatter at a set confidence level, and the higher the number, the more uneven the results.
| English | Volatility Index |
|---|---|
| Classification | Math & Probability |
| English | Volatility Index (VI) |
| Category | Math · Probability |
| Basis | Single-spin standard deviation × confidence level coefficient |
| Common confidence levels | 90% or 95% |
| Availability | Only in some test reports and game rules |
| Related | Volatility, variance and standard deviation |
Overview
The volatility index (Volatility Index, VI) expresses a slot’s volatility as a single number. Each provider labels volatility as “low, medium, high” or by a number of lightning icons, and these ratings use different standards at each company. VI has a mathematical definition, so it is good for comparing games with each other.
How it’s calculated
VI is calculated by multiplying the standard deviation of a single spin result by a confidence level coefficient.
| Confidence level | Coefficient (normal distribution basis) | VI |
|---|---|---|
| 90% | About 1.645 | 1.645 × σ |
| 95% | About 1.96 | 1.96 × σ |
For example, for a game with a single-spin standard deviation (σ) of 10, the 90% VI is about 16.45.
What you can do with VI
If you know the VI, you can roughly estimate what range the actual return will fall into over a given number of spins.
Actual return range ≈ RTP ± VI ÷ √(number of spins)
| Spin count | 90% range for a game with VI 16.45 and RTP 96% |
|---|---|
| 1,000 spins | About 44% to 148% |
| 10,000 spins | About 80% to 112% |
| 100,000 spins | About 91% to 101% |
| 1,000,000 spins | About 94.4% to 97.6% |
The larger the VI, the wider the range, so even with the same number of spins, the chance of winning big or losing big is greater. However, slot results are not normally distributed but have a shape where big wins are rare and clustered, so this calculation is a rough estimate.
Compared with volatility ratings
| How it’s shown | Upsides | Downsides |
|---|---|---|
| Rating (low, medium, high) | Easy to understand | Standards differ by provider |
| Lightning / icon count | Visible at a glance | Can’t tell the exact difference |
| Volatility index (VI) | Mathematically comparable | Few games publish it |
Where to find it
VI appears in the math documents of some offline slot machines and in test lab reports. Online slots rarely publish it, so a realistic approach for players is to judge by looking at max win, hit frequency, and the provider’s volatility rating together.