Interactive Tool · Math & Probability
Set your bankroll, bet size, RTP and volatility. Run 7,500 simulated sessions in your browser and see the honest probability distribution of outcomes — including expected loss, bust risk, and how often you'd finish ahead.
18+ only. Illustrative model — not a specific game's PAR sheet. Free support: BeGambleAware.org.
Illustrative model, not a specific game's PAR sheet. This simulator uses a simplified payout distribution designed so that the long-run expected return exactly equals the chosen RTP. It does not replicate any particular slot's actual math model, bonus structure, or volatility index.
Per-spin model: Each spin either wins or loses. Wins occur with a hit frequency h set by the volatility tier (Low ≈0.35, Medium ≈0.22, High ≈0.12). When a spin wins, the payout is drawn from a two-component mixture: a uniform distribution for small wins and an exponential distribution for rare large wins. The mixture parameters are calibrated so that E[payout per spin] = RTP × bet exactly — verified analytically and confirmed by a 10-million-spin self-test (error <0.35%).
Volatility: Low volatility means frequent small wins (low variance). High volatility means rare but potentially large wins (high variance). Both tiers produce the same expected loss per spin — volatility changes the shape of the outcome distribution, not the direction.
Monte Carlo: The simulator runs 7,500 independent sessions in your browser using JavaScript's Math.random(). Each session plays the configured number of spins or stops early if the bankroll reaches zero. Statistics are computed from the full distribution of session outcomes.
Sanity check: After each run, the simulator measures the realized RTP across all spins actually played (total payouts divided by total wagered). This is compared to the configured RTP — if they diverge by more than 1%, a warning is shown. In normal operation the realized RTP matches the configured value within 0.1%. Note: the mean final balance may differ from the simple formula bankroll − spins × bet × (1 − RTP) when a significant fraction of sessions end in early bust, because busted players wager fewer than the full spin count.
What this does not model: bonus rounds, free spins, jackpot contributions, max-win caps, or any game-specific feature. Real games deviate from this simple model in all of those dimensions. This tool illustrates the mathematical consequence of the house edge and volatility in isolation.
The house edge is unavoidable — it is built into the RTP at certification. A 96% RTP slot returns an average of €0.96 for every €1 wagered, so the casino keeps €0.04 per spin in expectation. No bet-sizing system, timing approach, or "session strategy" changes this. The longer you play, the more certain the loss converges to the expected value.
Volatility changes the ride, not the destination. A high-volatility game produces more sessions ending in large wins and more ending in early busts, but the average outcome across thousands of sessions is identical to a low-volatility game at the same RTP. If you saw a session end in a big win, that is genuine random variance — the next player's session is statistically independent.
Bankroll management can only extend or shorten a session — it cannot improve the expected return. Smaller bets relative to bankroll reduce bust risk by spreading variance across more spins, but the expected loss as a fraction of total wagered remains constant.
See also: RTP vs house edge · Volatility explained · Bankroll management · How slot RTP works · RTP versions explained.
Because slot outcomes are random. In a finite session, variance dominates and many individual runs beat the expected value — just as many runs lose more than expected. The simulator shows you the full distribution. Notice that even when a large share of sessions finish up, the average final balance is still below the starting bankroll — the expected loss always applies across enough sessions.
Increasing your bet per spin increases the expected loss per spin proportionally (expected loss = spins × bet × house edge). A €2 bet at 96% RTP costs twice as much in expected value as a €1 bet over the same number of spins. Larger bets also amplify variance — you can win bigger or bust faster.
This model captures the two things that matter most: the house edge (via RTP) and dispersion (via volatility). What it does not model is the specific structure of a real game — bonus rounds, multiplier trails, jackpot contributions, max-win caps, or scatter pays. Real game math is more complex, but the long-run expected return still equals the certified RTP. The fundamental lesson — that expected loss = spins × bet × (1 − RTP) — holds for any compliant certified game.
No. Each spin is statistically independent. A big win in this simulation, or in a real session, contains zero information about future outcomes. The expected value of every future spin remains negative (by the house edge). The simulator's job is to show you the full distribution — including the lucky sessions — while making the expected loss central and unavoidable.