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The Maths of Video Slots Explained

Online slots are the centrepiece of any online casino. Row upon row of thousands of fixed-odds gaming machines is an appealing proposition to any gambler. With so much choice, it can be hard to sort through these listings and find a suitable game. Some choose based on chance, others might look for a particular theme, or a developer whose game they know.

But one thing that should never be over-looked is maths! That’s right, not all slots run on the same game model, and variations in Return to Player, stake sizes, jackpots and volatility all contribute to significantly different experiences from one game to the next. So, in this guide we break down video slots into the constituent parts of their maths make-up, and whether you are a gambler looking to try a new title, or an operator or marketeer looking for an improved sales pitch for your product, this article will be of help.

Slot Game Return to Player (RTP)

Let’s start with Return to Player (or RTP as its shortened to). This refers to the average amount of money a game pays out in prizes as a percentage of the total wagered over time. Casino games vary in RTP. Some table games have an RTP of 99% or higher, but most slots come in at around 96%.

That means, for every $100 wagered, $96 is paid back out in prizes. We say ‘most slots’ because some can run at lower RTP levels. For example, Progressive Jackpots like Mega Moolah from Microgaming run at less than 90% because a portion of every bet is reserved for the jackpot total, taking away from base game prizes. Meanwhile, other games, like Thunderkick’s 1429 Unchartered Seas, run at 98.5%.

It’s worth looking for a slot game’s RTP – usually found on the casino website or in-game info screen – before playing, to make sure that it is offering a fair return on your stakes. You can also find the overall current RTP of individual casinos on review pages like this one – These numbers are usually audited by third parties like eCORGA to ensure that they are true and calculated correctly. They give you assurance that an operator is running games at a fair level for their customers.

Slot Game Variance

Next to RTP, variance or volatility is the most significant part of game’s maths profile in determining what kind of experience you will have when playing. The volatility tells you how far from the published RTP a game will vary during your session.

Low variance slots will remain close to the RTP throughout a players’ spins. This means the distribution of wins is fairly even and regular, if small-ish payouts will occur. High variance games deliver the opposite. Players may go through long periods of play where little or no return is experienced, before a rush of wins with huge payouts drops. This is due to the highly variable RTP built into the games maths model. Games like this are known as ‘high risk’ because the odds of wins are longer and players can burn bankroll quickly without getting anything back.

High variance slots are very popular despite their tough maths models and some of the biggest games of all time work like this. Good examples are Big Time Gaming’s Bonanza slot and Money Train 2 by Relax Gaming.

Stake Size and Jackpots

Of course, from a player’s perspective the stand-out figure on any game screen will be the jackpot size, often affected by how much they choose to stake. Jackpots vary from one game to the next, but typically high variance games offer larger top payouts. And of course, progressive jackpot slots are the only way to win multi-million-dollar prizes.

With online slots you will often find the prize levels expressed as a multiplier of the stake amount. For example, a 10,000x top prize would trigger a $10,000 payout if the player was staking $1 per spin.

In recent years, slot games jackpots have gone up in value as high variance developers look to deliver greater potential than their rivals. The very biggest prizes now are as high as 150,000x on games like San Quentin xWays by No Limit City from Sweden.

In general, depending on the jurisdiction a site is licensed in, casinos will give a broad range of stake options to players. Our recommendation if you are spinning a slot for the first time is that you choose a low-end wager of 10c or 20c as you get used to the gameplay and features. Then, when you are comfortable with how a slot works, you can increase your stake to aim for the bigger value prizes.

Final Thoughts

Video slots are the most popular games in any casino for a reason – they offer fast, fun and simple gameplay, with no strategy required! However, that doesn’t mean you shouldn’t give though to the game you choose next time you are preparing to spend some money online. Remember that RTP, variance and prize levels will interact to affect your gameplay, so choose wisely and based on your own attitude to risk and available balance.

Cathy Queen
Cathy Queen

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