How Do Online Slot Machines Work

There are tens of thousands of online slots with many different themes and to some extent, varying game mechanics, but how do they all work? The underlying workings of slots are all very similar.

how do online slots work

Conventional Slots

Physical slot machines that could be found in land based casinos originally had mechanical reels – there were typically 22 positions on each reel of a standard 3-reel machine which created 10,648 combinations (22x22x22).

With one top symbol occupying one position on each of the 3 reels, this theoretically meant the slot machine could offer a maximum top prize of $10,648 for a $1 bet (without taking the rest of the pay table into consideration).

If the slot machine offered a top prize of $10,000, the casino’s ‘edge’ or ‘hold’ would be $648 which equates to 6.48%.

The remaining 93.52% ($10,000) is called the Return to Player (RTP%). Most online slots offer an RTP of around 95% due to other winning combinations also available.

The Rise of The Online Slot Machine

When real money slots first started to turn digital in the mid 90’s, physical restrictions were lifted and game developers now had the opportunity to create virtual reels with as many positions as desired, resulting in the potential for much bigger wins.

For example: with 100 positions on each virtual reel, the number of combinations increases to 1,000,000. Now add in two more reels for what has become a modern day standard 5 reel slot, and we are looking at 10 billion combinations!

Offering a $10bn jackpot win for a $1 bet is just too risky and not commercially feasible, so more of the top symbols are added to each of the reels, which increases the chances of it landing and the top payout is adjusted accordingly.

Example: If there were 10 top symbols on each of the 5 reels with 100 positions on each, the probability of hitting that top prize is now 1 in 100,000 (10/100)5.

A series of smaller winning combinations are also added to create a game that pays out more regularly, but with less exposure for the casino.

It’s the game mathematician’s responsibility to create a paytable with the right balance of regular payouts and opportunities for big wins. A slot which concentrates on higher payouts with fewer smaller winning combinations will be known as High Variance or Highly Volatile.

Conversely, if there are many smaller winning combinations and less of the higher ones, it’s known as a Low Variance or Low Volatility slot.

How is a slot machine’s outcome determined?

The final positions of the reels and symbols are determined by a Random Number Generator (RNG). This is a computer-driven algorithm which attaches a value to each position on the reel and then randomly selects a reel position for the winlines.

The RNG is continually running in the background, therefore the outcome will be different depending on when you click ‘Spin’ – a fraction of a second sooner or later could mean the difference between nothing and a big win, making it entirely random!

Do Slot Machines Get Hot?

Contrary to popular myth, Free Slots That Pay Real Money do not have a ‘hot mode’. Or in fact, any type of memory, whatsoever. Neither is it true that a slot is likely to go cold and is unlikely to pay after a big win. It’s entirely possible to hit two major wins back-to-back.

Every single spin on a slot machine is a unique event and previous game rounds have no influence over the following outcome. If you want to stay ahead, you need to take advantage of offers like valid $500 No Deposit Bonus Codes.

What is a Bonus Feature?

Many online slots are free slots with free spins feature which is usually triggered when 3 or 4 Scatter symbols are visible anywhere in the game window – that is to say, they don’t need to be on a winning payline.

The Bonus Feature will usually consist of 10 free spins in which you can win bigger payouts, often with an ever-increasing multiplier.

Bored of waiting to hit the Bonus Feature? Some free slots with bonus rounds and free spins allow you to buy the Bonus Feature. It’s exciting, for sure – but it can cost you around 100x your bet!

Check out our slot reviews including the latest Megaways slots which have been taking the slot world by storm over the last couple of years.


Riku is the Editor in Chief at BonusFinder and is a global expert in casino, sports betting and poker.