Slots Odds, Winning Probabilities and House Edge
If you have tried any type of online gambling, you will probably know that the odds generally favour the house. Whatever game you choose, the casino retains an advantage. That margin varies by game, and slot machines are often among those offering the least favourable odds. Even so, losing is not guaranteed on every spin. Slots differ in their probabilities, house edge and potential payouts, so some may return more than others over time.
An Introduction to Slot Machines
Slot machines have been around for over a hundred years, although they became especially prominent in the 80s and 90s. Their straightforward format helps explain why they remain popular in both land-based and online casinos.
There is little to learn before playing. You do not need to master complicated rules, bet types or casino etiquette: press the spin button and wait to see whether a winning combination appears on the reels. By comparison, Craps, Blackjack and Roulette generally require some knowledge to play, or at least to play competently. A button or lever starts the spin, and the machine supplies the result. Slots can also provide relatively inexpensive entertainment, provided you play responsibly. Smaller wagers are available, which is why some are called ‘Penny slots’.
You can play slot games online or visit a land-based casino, although this guide later explains why the odds of winning are lower in the latter. In either setting, casino slots are regulated to support fair and random outcomes. Regulation does not remove the house advantage, but there are several considerations that may help you make more informed choices.
How do Slot Machines Work?
A spin takes less than a second, and the outcome is selected when the button is pressed. Every slot machine game relies on a random number generator (RNG), which is a software algorithm assigning a result to each spin. It cycles through as many as millions of possible outcomes before stopping on one of them at the microsecond the spin command is given.
After a losing streak or two, some players claim that gaming-industry slot machine random number generators are rigged. They are not, discussion. Independent third-party testing companies examine these systems to check for fair, random results. Rigging would also expose slot developers to a substantial risk of being discovered quickly.
Slot Odds Explained
Slots are among the easiest, if not the easiest, casino games to play online. Their accessibility is a major reason for their popularity: you can select a game, spin the reels and hope for a payout. Understanding how likely that payout is, however, is considerably more complicated than starting the game.
The RNG cycles through the numerous possible reel outcomes, with the aim of producing a fair and entirely random result.
Reel symbols, their payout values and any bonus features all influence what a spin can win. The available combinations, hit probability, payouts and RTP together shape the odds associated with a slot game.
Slots Probability and RTP
Probability describes how likely an event is to occur. It is expressed as the ratio of possible positive results to the total number of possible outcomes. The same idea is used when estimating the chance of rain storms or when car insurers assess the likelihood that you will have a car accident.
Online slots use software and algorithms that assign different probabilities to symbols landing in winning reel combinations. The proportion a slot returns from the money it has taken over a long period is known as its Return to Play or RTP.
Many online casinos and/or software providers publish a game's RTP, although some do not. RTP is never 100%, because a casino would otherwise have no statistical advantage. The gap between the stated RTP and 100% is the online slot's house edge. Viewed from the player's side, that same relationship is sometimes described as the odds of winning.
For example:
Suppose an online slot shows an RTP of 95% over an extended period. It would return 95% of the money wagered into it and retain the remaining 5% as profit, making 5% the house edge. In simple terms, spending $100 could produce $95 back.
That example is only a simplified illustration because the RNG determines when and how payouts occur. RTP does not calculate a separate return for your own money, so receiving exactly 95$ from your $100 is unlikely. One player's spin could produce $300 from their $100, while another player could lose their $100 completely.
Slot Volatility Explained
Volatility, also called variance, is another factor affecting how a slot distributes payouts across its RTP. It describes both the size of the wins and how often those wins occur.
- Low Variance: Low-volatility slots tend to have a higher hit rate, so winning results appear more frequently. Those regular payouts are generally smaller than wins on higher-volatility games. A low-variance slot may pay as often as every couple of spins, although the amount may still be insufficient to cover the spins that produced it.
- High Variance: High-volatility slots take the opposite approach. Wins arrive less often but can be larger when they do. These games commonly feature bigger jackpots or lucrative bonus rounds that trigger rarely.
- Medium Variance: Medium-variance slots sit between the other two categories. They tend to pay more often than high-variance games while producing larger average wins than low-variance slots.
Players often have clear volatility preferences. High rollers with larger budgets may choose high-variance slots because their bankroll can withstand a run of winless spins while waiting for a substantial result. Someone with a smaller bankroll may prefer low-variance games, which could keep the balance active for longer.
Online Slots vs. Brick-and-Mortar Slot Machines
The place where you play can affect the slot odds available to you. Online casinos and land-based venues differ in several important respects.
Playing Slots Online
Convenience is the clearest advantage of playing online. You can play at home, on the bus to work or elsewhere with an internet connection. Online play also removes the need to wait for a seat or navigate a crowded casino floor before reaching the game you want.
Online casinos also offer a much broader selection of games and stakes. Thousands of current slot titles are available, including progressive jackpot slots, classic slots and Megaways slots. Many can be tried without risking real cash through a free demo mode.
Online play is also presented as having better odds, because online slots have an average RTP of 96%. As the following section explains, that average is considerably higher than the stated average for land-based casinos.
Playing Slots at Brick-and-Mortar Casinos
Online play is convenient, but land-based casinos can provide a more complete social and sensory experience. You can dress up for a visit to a luxurious venue, enjoy its sights and sounds, eat in a restaurant or have a quick drink at the bar. Some casino properties also include nightclubs.
The principal drawback of brick-and-mortar venues is that their machines have much lower average RTPs. This is not necessarily because casinos intend to treat players unfairly; their operating costs are higher than those of online casinos. Staff, larger energy bills, rent and other overheads must be paid, so the games generally offer less favourable odds.
Land-based casinos can have slots with payout percentages as low as 80%. Some machines still offer a stronger RTP. Wheel of Fortune, for example, is a three-reel slot with a single payline whose RTP is 96.08%, higher than that of most land-based slots discussed here.
The Best Slots Odds
Nearly 1,500 new online slot releases arrive each year, in addition to the many thousands already available. Identifying the games with the best odds can therefore take time. GCCans highlights several high-RTP slots that may be found at many top online casinos. Compared with the money they accept, the titles below return more than many other slots. They are among the closest examples to winning slots, although statistical results still mean players lose over time. Here is what each one offers:
- Book of 99 (Relax Gaming) - 99%
Relax Gaming's 'Book of 99' video slot is often cited among the stronger slot-odds options at reputable online casinos. In this Slots Odds, Winning Probabilities and House Edge guide, Evan Carrington and GCCans explain that the 99 in its title points to the game's RTP of 99%. Statistically, that represents a theoretical return of 99% of money wagered over a long period; it does not promise a winning session or make every spin profitable.
Book of 99 belongs to the 'Book' slot style. Alongside its high payout percentage, it includes the familiar free spins feature with an expanding symbol. There are no additional bonus rounds, but a wild collection feature can create payouts and may also unlock the free spins bonus.
- Blood Suckers (NetEnt) - 98%
High payout percentages are not limited to newly released video slots. NetEnt launched Blood Suckers in 2009, and its payout percentage remains higher than that of most online slots. That return has been a major part of the game's success from its release to the present discussion.
Blood Suckers uses five reels, three rows and 25 fixed paylines. Its features include wild symbols, a picking game and a free spins bonus. The game has low volatility and often produces a win every other spin. Combined with its high payout percentage, that low variance may appeal to players seeking strong odds while working with a smaller bankroll.
- Jokerizer (Yggdrasil) - 98%
Yggdrasil's Jokerizer is another choice for players looking for a high-RTP slot. Its stated RTP is 98%, placing its slot machine odds among the strongest in this selection. The house advantage is 2%, a figure similar to the one associated with blackjack.
On the surface, Jokerizer is a relatively simple machine with 5 reels, 3 rows and 10 fixed paylines. Its in-game features are Mystery Win, which can award up to 6,000x the stake, and wild symbols. Because it has medium to high variance, it may not suit a smaller bankroll.
- Zeus Lightning: Power Reels (Red Tiger Gaming) - 97.73%
Red Tiger Gaming has also released high-RTP online slots over the years. One of its strongest examples is Zeus Lightning: Power Reels, an Ancient Greek-themed game with seven reels, 6 rows and 30 paylines. Its stated RTP is 97.73% of the money it receives, placing it among the options highlighted for players seeking better online slot odds, rather than guaranteeing a winning result.
Its features include Expanded Lightning, which enlarges one symbol type until it fills the reels. A free spins feature can also award spins with up to three wild symbols appearing on the reels.
- Blood Suckers Megaways (Red Tiger Gaming) - 97.66%
Blood Suckers Megaways is another high-RTP title from Red Tiger Gaming. It is the sequel to Blood Suckers, the earlier slot noted for its strong return to player percentage. This game has a slightly lower payout percentage of 97.66%, but its maximum win is higher, reaching 20,521x the stake.
The minimum bet is 0.10 and the maximum is 4.00, both relatively low compared with those of some other slot machines. That range may be sufficient for a casual player. Bonus content includes base-game modifiers such as random wilds, super wilds and a win multiplier, along with free spins that can be triggered or purchased through the buy bonus feature.
Can You Improve the Slot Odds?
You cannot alter a slot machine's underlying odds: its RNG produces random results in line with the slot's RTP. What you can do is consider the many available slot-playing tips and apply the ones that support more informed, responsible decisions.
Choosing a game with a high RTP may improve the long-term mathematical position, while progressive jackpots are often avoided because their large prizes generally come with a lower RTP. Bankroll management can also help you play for longer by limiting excessive wagers and controlling the length of a session. None of these choices guarantees a win.
Casino bonuses can provide another way to play with less of your own money, subject to their terms. When you sign up at casino sites, you may encounter no deposit bonuses, welcome bonuses and free spins. If a bonus session produces a win, it can add funds to your bankroll, but wagering conditions still apply.
You could also encounter betting systems such as the Martingale, although these are generally more suited to 50/50 casino games such as Roulette and Baccarat. Modified versions may be promoted as ways to extend a winning streak or reduce losses, but no system can guarantee profits or overcome the game's underlying odds.
