The one rule that matters
Never bet more per spin than 2% of your session bankroll. Everything else is decoration on top.
At 2% per spin:
- A €200 session bankroll → max €4/spin.
- A €500 session bankroll → max €10/spin.
- Under €100 session bankroll → play stakes of €0.20-€0.50, or don’t play.
This bet-fraction is small enough that even a very-high-volatility slot can absorb a few dozen losing spins in a row without busting.
Session vs total bankroll
Two separate numbers:
- Total bankroll — money set aside for casino play across weeks / months. Treat as sunk if lost. Never top up from personal money.
- Session bankroll — the slice you bring to a single session (a session = ~30–90 minutes of play).
Rule of thumb: session bankroll ≤ 1/10 of total bankroll. So a €2,000 total → €200 sessions max. This gives you 10 independent shots at a positive-tail outcome.
The ruin-probability lens
For a slot with per-spin mean loss m (e.g., −0.035 × bet at 96.5% RTP) and stddev s (e.g., 4× bet at medium volatility), the probability of busting a bankroll of B before completing a wagering requirement of turnover T is well-approximated by:
P_ruin ≈ Φ(−B / (s × √(T / bet)))For a €200 bankroll, €1 bet, 96.5% RTP, medium vol, wagering target €4,000: P_ruin ≈ Φ(−200 / (4 × √4000)) ≈ Φ(−0.79) ≈ 21%.
Cutting bet to €0.50 halves the stddev term but doubles required spins — net effect: ~15% ruin. Cutting bet to €0.20 → about 8%.
The lower your bet-fraction, the higher your chance of surviving to cash out. This is why the 2% rule works — it puts you comfortably in the “usually survives” zone.
Stop-loss and stop-win
A pre-committed stop is the highest-EV thing you can add to a session:
- Stop-loss: end the session at 50% of starting bankroll. Prevents you from turning a normal losing streak into a total bust.
- Stop-win: end the session at 200% of starting bankroll. Locks in an above-average outcome. Withdraw, don’t reinvest.
Written down before the session, honored during. Most losses come from ignoring both.
The Kelly criterion — why we don’t use full Kelly here
The Kelly criterion (bet size = edge / odds) is optimal for positive-EV bets. Casino slots are negative-EV bets, so full Kelly says: don’t bet. That’s technically correct.
The way Kelly bends to bonus play: your total expected value comes from the bonus grant, not the slot returns. If a €100 bonus has +€25 EV and you clear it in one session, you’re implicitly running Kelly on the +€25 expected profit, not the −3.5% slot return. That’s why bonus-driven play can be sustainable even though pure slot play cannot.
Practical setup
- Fund a total bankroll of €X. Never top up.
- Allocate €X/10 per session, max.
- Pick bet ≤ 2% of session bankroll.
- Set stop-loss at 50%, stop-win at 200% on the session bankroll.
- Prefer bonuses with positive EV (see /bonuses) — turns the game from “how fast do I bleed” into “how often do I hit the tail”.
- Session log: date, casino, bonus claimed, deposit, bet, spins, outcome. Real data beats emotion after 20 sessions.
When to walk away
Two triggers you should honor without renegotiation:
- You feel a compulsion to top up your total bankroll — that’s the moment gambling stops being a leisure choice. See BeGambleAware or your local equivalent.
- You catch yourself trying to “win back” a loss — the math of chasing losses is strictly worse than starting fresh. Close the session, cool off 24 hours minimum before reopening.
Bankroll management is not a strategy for making money. It’s a structural constraint that keeps casino play a hobby.