What the calculator shows
Variance is the difference between what you should win, based on your win rate, and what actually happens over a sample of hands. The calculator uses three numbers: your win rate (bb/100), your standard deviation (bb/100) and the number of hands. With them, it shows your expected result, the range your result falls in 70% and 95% of the time, the chance of ending up losing and the bankroll that keeps your risk of ruin at 5% or 1%.
The chart draws 20 possible runs with the same numbers. They are all the same player: the only difference between them is luck.
Which standard deviation to use
Standard deviation measures how much your results swing every 100 hands. Your number is in PokerTracker or Hold’em Manager. Without it, start with 90, a common value for 6-max no-limit hold’em. Games with more action, like Omaha, swing a lot more: use your real number whenever you can.
Why rakeback lowers the bankroll you need
Rakeback doesn’t change how much the hands swing, but it raises your win rate, and the bankroll you need drops quickly as your win rate goes up. With a 5 bb/100 win rate and a deviation of 90, the bankroll for a 5% risk of ruin is about 2,430 bb. If rakeback adds 2 bb/100 (for example, 40% of 5 bb/100 in rake), your win rate goes to 7 bb/100 and the bankroll drops to about 1,730 bb.
To see how much comes back to you at each site, use the rakeback calculator.