This slot machine simulator lets you play two play-money machines whose odds are printed in full: the exact RTP, how often each spin pays, and how wildly results swing. Both machines return about 95% of what is staked over the long run, and they feel completely different to play.
The chips have no value and cannot be cashed out. Nothing here is a prediction of what any real machine will do, but the maths works the same way, which is the reason to try it.
How does this slot machine simulator work?
Each machine has three reels with 32 equally likely stops each, and only the middle line pays. You pick a bet, press Spin, and the reels land independently. A pay table drawer under the reels lists every winning combination, how often it happens, and how much of the total return it provides.
- Machine 1 (low volatility) pays small amounts often. A single cherry pays your bet back, and the top prize is 200 times the bet.
- Machine 2 (high volatility) pays rarely. A single cherry pays nothing, and the top prize is 1,000 times the bet.
- Spin 100 runs 100 spins at your current bet and totals them.
- Simulate 2,000 sessions of 500 spins plays 1,000,000 spins in a moment and shows how the end results are spread out.
You start with 1,000 play chips. A break reminder appears after 15 minutes of play, and nothing is saved to your browser or sent anywhere.
What are the exact odds and RTP of each machine?
Machine 1 returns 95.01% of every stake on average and Machine 2 returns 94.92%. That is a house edge of 4.99% and 5.08%. Both numbers come from counting all 32,768 possible reel outcomes (32 x 32 x 32), not from a sample, so there is no rounding in the odds tables below.
Machine 1 (low volatility). Symbols per reel: one seven, two BARs, three bells, eight cherries, 18 blanks.
| Result | Pays (x bet) | Chance per spin | About 1 in | Share of the 95.01% return |
|---|---|---|---|---|
| Three sevens | 200 | 0.003% | 32,768 | 0.6% |
| Three BARs | 40 | 0.024% | 4,096 | 1.0% |
| Three bells | 15 | 0.082% | 1,214 | 1.3% |
| Three cherries | 5 | 1.56% | 64 | 8.2% |
| Two cherries | 3 | 14.06% | 7 | 44.4% |
| One cherry | 1 (stake back) | 42.19% | 2.4 | 44.4% |
Machine 2 (high volatility). Symbols per reel: two sevens, four BARs, four bells, seven cherries, 15 blanks.
| Result | Pays (x bet) | Chance per spin | About 1 in | Share of the 94.92% return |
|---|---|---|---|---|
| Three sevens | 1,000 | 0.024% | 4,096 | 25.7% |
| Three BARs | 200 | 0.195% | 512 | 41.2% |
| Three bells | 50 | 0.195% | 512 | 10.3% |
| Three cherries | 10 | 1.05% | 96 | 11.0% |
| Two cherries | 1 (stake back) | 11.2% | 9 | 11.8% |
Look at the right-hand column of Machine 2. Almost two thirds of its return comes from the two biggest prizes, which happen about once every 455 spins between them. A player who never reaches them sees a machine paying far less than 94.92%, which is exactly how high volatility works.
What do RTP, hit rate and volatility mean?
RTP (return to player) is the share of all money staked that a machine pays back over a very long run. House edge is what is left: 100% minus RTP. A 95% RTP means 5 units of every 100 staked are kept on average. RTP says nothing about how often you win or how big the swings are.
Hit rate is how often a spin pays anything at all. Volatility (or variance) is how widely results spread around the average. Two machines can share an RTP and differ in both.
| Measure | Machine 1 | Machine 2 |
|---|---|---|
| RTP | 95.01% | 94.92% |
| House edge | 4.99% | 5.08% |
| Hit rate (any payment) | 57.92% | 12.68% |
| Spins that pay more than the bet | 15.73% | 1.46% |
| Standard deviation per spin (in bets) | 1.72 | 18.09 |
What happens to a bankroll over 100 or 500 spins?
Over 500 spins at one chip a spin, both machines lose about 25 chips on average, but the middle of the range differs enormously. Machine 1 stays close to the average. Machine 2 usually loses far more than the average and sometimes wins a lot, because a few rare big pays are carried by the mean.
| Machine and length | Average result | Bad session (1 in 20) | Median | Good session (1 in 20) | Finished ahead |
|---|---|---|---|---|---|
| Machine 1, 100 spins | -5 | -25 | -7 | +18 | 28% |
| Machine 1, 500 spins | -25 | -73 | -29 | +29 | 18% |
| Machine 2, 100 spins | -5 | -91 | -71 | +176 | 21% |
| Machine 2, 500 spins | -25 | -398 | -148 | +866 | 32% |
The table shows something surprising: Machine 2 leaves more sessions ahead after 500 spins than Machine 1, yet its median session is much worse. A few sessions hit the big prizes and win a lot; most lose more than the average. The average and the typical outcome are not the same number. Press the Simulate button to see your own version of this table.
Why can a slot machine feel as if it pays often when it does not?
Machines can pay less than your bet and still celebrate with lights and sounds. These are called losses disguised as wins. In a study of one multi-line video slot, 18.4% of outcomes on 15 lines were of this kind, and players’ bodies reacted to them more like wins than losses.
Hit rate is easy to misread for the same reason. Machine 1’s 57.92% hit rate sounds high until you see that 42.19 points of it are single cherries, which only give the stake back. Only 15.73% of its spins pay more than you bet. This is why you should judge a machine by RTP and by the size of its swings, not by how often something lights up.
Are slot machines random, and can a machine be due a win?
Real slot machines use a random number generator, and each spin is independent of the last. The result is decided when you press the button, and the reels are a display. No machine is due a win after a long losing run, and the time of day, bet size and button timing do not change the outcome.
The reels on a real machine are usually weighted, so a symbol can look rare or common regardless of the physical reel. Our machines show the same idea in the open: each reel has 32 stops with the symbol counts above, and the odds follow from the counts. The gap between what the reels seem to show and the maths is why a near miss feels closer than it is.
How is a free slot machine game different from a real or online slot machine?
A free slot machine game uses the same ideas as a real or online slot machine, but no money is staked. Real-money online slots add deposits, faster play and bonus features, and publish their own RTP in the game information screen. In the UK, rules require the RTP, the house edge and the likelihood of winning events to be available before you commit to gamble.
Speed changes cost. At 500 spins an hour (an assumed pace) and a 1 unit bet, a 5% edge costs about 25 units an hour. At twice the speed the average cost doubles. Use our slot machine calculator, the RTP and volatility calculator or the expected loss calculator to price your own session.
Real machines are set to regulator minimums. New Jersey requires a theoretical RTP of at least 83% for slot games. A Canadian responsible-gambling program puts the typical house advantage of slot machines at about 8%. Both are consistent with the 5% on our two machines being on the generous side, so do not read this page as a guide to the machine you may meet in a venue. Check the posted RTP where it is shown.
Does playing free slot games make real gambling more likely?
Studies of young people find that playing simulated gambling games goes along with gambling for money and with problem gambling. A 2022 Australian survey of 12 to 17 year olds found that link but could not show cause. Slot machines in particular are fast, and one small experiment found that players held back their responses less as the time per spin was shortened.
This page is for adults who want to understand the maths. It has no prizes, levels, bonuses or free-spin offers. If you find yourself wanting to keep spinning, open the Safer play toolkit or Get help.
What should you try next?
- Play 200 spins on each machine at the same bet. Which one felt better? Which one ended better?
- Press Simulate 2,000 sessions on both machines and compare the best 5% and worst 5% of sessions.
- Compare Machine 1’s 57.92% hit rate with the 15.73% of spins that pay more than the bet.
- Work out what a real session would cost with the gambling session cost calculator.
How to read your session
After each spin the panel shows chips, net result and the average expected result at the machine's RTP. The simulation shows how 2,000 sessions of 500 spins end: worst 5%, median, best 5% and the share that finish ahead. The average result drifts to the RTP only over very long play.
How it is calculated
All 32 x 32 x 32 = 32,768 reel outcomes are counted. RTP is the sum of each result's pay multiplied by its number of outcomes, divided by 32,768. Machine 1: 31,133 / 32,768 = 95.01%. Machine 2: 31,105 / 32,768 = 94.92%. Hit rate is the share of outcomes that pay anything. Standard deviation is the square root of the average squared pay minus the squared average pay.
Worked example
Worked example
Machine 1 at 1 chip a spin: 500 spins staked 500 chips and an average result of -25 chips. Machine 2 gives the same -25 on average but a 5% bad session loses about 398 and a 5% good session wins about 866.
Limits
These are not real slot machines. Real machines have more symbols, lines, features and different RTP, and the figures above do not apply to them. Session results come from a random simulation and vary between runs.