Full explanation
There is no exact answer, because variance does not respect budgets. But a useful planning guide for a medium-volatility slot is to bring 200 to 300 times your bet per spin if you want a realistic shot at lasting 500 spins.
- At 0.10 a spin: roughly 20 to 30.
- At 0.20 a spin: roughly 40 to 60.
- At 1.00 a spin: roughly 200 to 300.
The logic behind the range: with about 36.6% of spins returning something, most of it small, your balance bleeds slowly between features. The buffer is there to keep you in the game long enough to catch a Mystery chain or a bonus, which is where any recovery comes from. Bring too little and a normal dry run ends your session before the feature ever shows.
Two honest caveats. First, this is survival, not profit. A bankroll that lasts 500 spins is not a bankroll that wins; it just buys you time. Second, set the number as a hard loss limit before you start and stop when you hit it. The math above helps you plan a session, not beat the house edge, which is always working against the bankroll.
Turn the estimate into a rule
The 200 to 300 times bet guideline is only useful if you commit to it as a hard limit. Decide the number before you start, treat it as the most you will lose in the session, and walk when it is gone. Variance will sometimes end you early anyway, and that is normal.
It also helps to set a stop-win. If a feature doubles your starting balance, banking some of it protects the session from giving it all back during the next dry run. None of this changes the house edge, but it does keep a planned session from turning into chasing losses, which is where the real damage happens.
A workable starting point is to divide the bankroll you are comfortable losing by roughly five hundred and use that as your bet. It will not guarantee you reach the last spin, but it gives the medium variance room to breathe. Adjust down if early swings feel sharp, and never top up mid-session to keep a target alive.