This calculator uses a normal approximation (same core idea used by many poker variance tools). Results are estimates, not guarantees.
What the PrimeDope Variance Calculator Is Doing
A variance calculator estimates the range of likely outcomes for a poker sample based on your win rate, standard deviation, and volume. If your true win rate is positive, you can still have losing stretches because short-term outcomes are noisy.
The point of this tool is not to predict your exact graph. Instead, it helps you answer practical questions:
- “How normal is this downswing?”
- “What results are realistic after 50k, 100k, or 250k hands?”
- “What bankroll should I keep to survive ordinary variance?”
Input Fields Explained
1) Win Rate (bb/100)
This is your expected long-term edge measured in big blinds per 100 hands. Example: a 4.5 bb/100 winner expects +4.5 big blinds every 100 hands in the very long run.
2) Standard Deviation (bb/100)
Standard deviation measures volatility. No-limit cash players often see values around 70–120 bb/100, depending on game type, style, and table dynamics.
3) Number of Hands
As volume increases, your expected value grows linearly, while uncertainty grows more slowly (with the square root of hands). This is why large samples are more informative than short ones.
4) Confidence Interval
A 95% interval means “if the assumptions are correct, about 95 out of 100 equal samples should land inside this range.” It does not mean the middle of the range is guaranteed.
Core Math Behind the Calculator
Expected result (bb) = winRate × (hands / 100)
Sample standard deviation (bb) = stdDev × √(hands / 100)
Confidence range = expected ± z × sampleSD
The z-value comes from your selected confidence level. For 95%, z is approximately 1.96.
How to Interpret Your Output
- Expected Result: your mean outcome if repeated many times.
- Confidence Interval: a plausible range for one sample of this size.
- Probability of Loss: chance your final result is below 0 bb.
- Probability Below Target: chance of finishing below any custom threshold you choose.
Example Scenario
Suppose you play 50,000 hands at 4.5 bb/100 with 85 bb/100 standard deviation. You are a winning player, but there can still be ugly stretches. A non-trivial chance of breaking even or losing is normal at this volume, especially if your true edge is smaller than estimated.
This is exactly why bankroll management matters: variance can be painful before long-term edge fully shows up.
Practical Tips for Real Use
Use conservative assumptions
Most players overestimate win rate and underestimate volatility. Use realistic numbers from meaningful samples.
Stress-test your bankroll
Run this calculator with lower win rate and higher standard deviation than your “best guess.” If the downside still looks survivable, your plan is more robust.
Review in blocks
Recalculate at 25k, 50k, and 100k-hand checkpoints. This gives a better feel for expected swings over time.
Limitations
- Assumes stable win rate and stable volatility across the sample.
- Uses a normal approximation, which is very useful but still simplified.
- Does not model changing stakes, tilt effects, game selection changes, or rakeback promotions.
In short: use this as a decision aid, not as a crystal ball.