What this simulates
The calculator plays your session 1,500 times using the exact paytable and binomial probabilities for the board you chose, and reports how often the bankroll lasted the whole session, how often it touched your target balance at any point, and the spread of ending balances. It is a Monte Carlo simulation, so results shift slightly each run — that is variance, not a bug.
How to use it
Start with the defaults: CA$200, CA$4 a drop, 16 rows high, 500 drops. Survival is usually around 40%. Now switch to low risk and watch it jump above 95% with an almost identical expected ending balance. The house edge did not change — the shape did. Then try a bet of 0.5% of bankroll instead of 1% and see survival climb again.
Rules of thumb that fall out of the numbers: on high risk, bet no more than 0.5% of your bankroll per drop if you want to see the session through; on low risk, 2% is survivable; and doubling the target from 2× to 4× the bankroll roughly quarters the chance of reaching it.
The "expected ending balance" is the same on every board — bankroll minus 1% of turnover — which is the whole argument for choosing a site with rakeback. Rainbet's BOOST20 returns 20% of that expected loss every week.