How RTP Works in Slot Machines

How modern slot machines are built — from reels and RNG to the math behind RTP.

RTP — or Return to Player — is one of the most important metrics in gambling. It’s essentially a built-in commission that you pay for the privilege of playing. When you bet $100, part of that wager goes to the casino and the rest theoretically returns to players over time.

RTP + House Edge = 100%

This doesn’t happen with every spin, but as a mathematical expectation — in theory. When people talk about RTP, they mean theoretical RTP measured over a very large number of plays. How long that “long run” needs to be depends on volatility, and it varies from one game to another.

You can bet $100 on red and lose — your actual RTP is 0%, and the house edge is 100%. Or you can win and double your money — that’s 200% RTP and 0% house edge. These are examples of actual RTP, but over time the casino will always take its share. Eventually, the actual RTP converges with the theoretical one.

---

How it works

Take a simple example: flipping a fair coin. There are two possible outcomes — heads or tails — with a 50% chance, or 1 in 2.

If you bet $200 and the payout for guessing correctly is $400 (a 2x return), RTP is 100%. Nobody loses. The odds are 1 in 2, and the payout is 1 in 2.

If the payout is reduced to $360, RTP becomes 80%. The odds are still 1 in 2, but now the payout is 1 in 1.8 — the casino keeps 20% as a commission.

That’s how RTP is formed: by paying out probabilities at a slightly worse rate than their true odds.