Casino RTP Explained
Understanding Variance, House Edge, and Your Actual Session Results.
Theoretical RTP vs. Your Actual RTP
Theoretical RTP (Return to Player) is a percentage a game (like a slot machine) is programmed to pay back to players over a very long time—often millions of spins. A game with a 96% RTP will, in theory, return €96 for every €100 wagered. The remaining 4% is the casino's built-in profit, known as the "house edge".
Our calculator, however, measures your **Actual Session RTP**. This is the real return you experienced during a single playing session. Due to short-term luck, or "variance," your session RTP can be wildly different from the game's theoretical RTP. A session RTP over 100% means you had a profitable session.
Using the Calculator: Simple vs. Detailed Mode
Our tool offers two modes to make calculating your session RTP as easy as possible:
- Simple Mode: Use this mode if you already know the **total amount of money you wagered**. This is useful if the casino provides a session summary or if you are tracking your wagering for a bonus. You just need your start balance, end balance, and the total wagered amount.
- Detailed Mode: This is the perfect mode if you played with a **consistent bet size per spin** (e.g., €0.20 per spin) but don't know your total wagered amount. You provide your start/end balance, your bet per spin, and the total number of spins, and the calculator automatically works out the total wagered amount for you.
Why Your Results Vary: The Law of Large Numbers
Why was your session RTP 40% on a 96% RTP game? The answer is **variance**. In the short term, results are dominated by luck. Over the long term, math takes over.
The "Law of Large Numbers" states that the more times you repeat an experiment (like spinning a slot), the closer your average result will get to the expected value. The table below shows how the potential deviation from the theoretical RTP shrinks as the number of spins increases:
| Number of Games Played | Range +/- from Theoretical RTP |
|---|---|
| 50,000 | +/- 4.90862% |
| 100,000 | +/- 3.47092% |
| 200,000 | +/- 2.45431% |
| 500,000 | +/- 1.55224% |
| 1,000,000 | +/- 1.09760% |
† This table illustrates how variance decreases over a large sample size.
As you can see, after **50,000 spins**, the deviation from the theoretical RTP can be approximately **+/- 4.91%**. As the number of spins increases, this deviation shrinks because luck begins to even out. After **1,000,000 spins**, the deviation is just **+/- 1.0976%**, which is much closer to the expected RTP. This is why casinos are always profitable: they aren't relying on the outcome of your 100 spins; they are relying on the mathematical certainty over millions of spins from all players combined.
How This Connects to Our Tool
Our **Casino RTP Calculator** is a powerful tool for self-assessment. It helps you quantify your luck in any given session and track your play for responsible gaming or for monitoring bonus wagering requirements.
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