Expected Value Expected Value (EV)
The average value you get per try if you repeat a choice countless times. In slots it is calculated as "bet × (RTP - 100%)", and it is almost always negative.
| English | Expected Value (EV) |
|---|---|
| Classification | Math & Probability |
| English | Expected Value (EV) |
| Category | Math and probability |
| Formula | Σ (probability of each outcome × value of that outcome) |
| In slots | Bet × (RTP - 100%) |
| Example | 1,000 KRW bet, 96% RTP → -40 KRW per try |
| Related | RTP, house edge, volatility |
Overview
Expected value (EV) is the average value you get per attempt when you repeat a choice a very large number of times. It’s a basic concept in probability theory, found by multiplying each outcome’s value by its probability and adding them all up.
Expected value = Σ (probability of each outcome × value of that outcome)
A simple example
Say there’s a game where you pay 1,000 KRW, flip a coin, and receive 1,900 KRW if it lands on heads.
| Outcome | Probability | Result | Probability × result |
|---|---|---|---|
| Heads | 50% | +900 KRW | +450 KRW |
| Tails | 50% | -1,000 KRW | -500 KRW |
| Expected Value | -50 KRW | ||
It’s a game where you lose 50 KRW on average each time you play. This game’s “RTP” is 1,900 × 50% ÷ 1,000 = 95%, and the house edge is 5%.
Expected value in slots
Slots have too many possible outcomes to calculate by hand, but the RTP published by the provider is exactly that calculation result. So the expected result of a single slot spin can be found like this.
Expected result of one spin = bet × (RTP – 100%)
| Bet | RTP | Expected result of one spin | Expected result over 1,000 spins |
|---|---|---|---|
| 1,000 KRW | 97% | -30 KRW | -30,000 KRW |
| 1,000 KRW | 96% | -40 KRW | -40,000 KRW |
| 1,000 KRW | 94% | -60 KRW | -60,000 KRW |
As long as RTP is below 100%, the expected value is negative. This gap is the house edge, and it’s the reason the game can keep operating.
Expected value vs. actual results
Expected value is an “average,” not “this round’s result.” Because of volatility, actual results scatter widely around the expected value. In low-volatility games, results cluster near the expected value, while in high-volatility games they spread out toward big wins or big losses. The more times you repeat, the closer the average result gets to the expected value (the law of large numbers).
Expected value of bonus buy and ante bet
If a game is designed so that RTP is nearly the same with bonus buy or ante bet, the expected value per unit bet is nearly the same too. However, since you spend more at once, the expected loss in amount over the same time grows accordingly.