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Online Slots - How they work & how to play them, a complete Guide in 2023

Slot Machine

Online slots are the most popular type of game at internet casinos today. While blackjack, roulette, video poker, and other casino fare are also widely enjoyed, slots online generally represent the most frequently played titles, and they are usually the category with the most different games present at your average online casino.

If you want to delve deeply into the world of real slots online, then keep reading. We’ll explain what slot machines are, how they work, interesting features contained in some of the top slots today, and a lot more. Our highly ranked reviews of well-known online slots (linked at the bottom of this page) may even help you find a new favorite slot to play.

Online Slots

What Is a Slot Machine?

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First things first: What is a slot machine? You probably already know the answer to this, but it can’t hurt to review the basics before proceeding any further.

A slot machine consists of a series of cylindrical reels, arranged from left to right. These can be physical reels in a brick-and-mortar gambling hall or virtual reels modeled on computing hardware.

Upon activation of the mechanism – by pulling a lever, pushing a button, or clicking onscreen – these reels begin rotating forward toward the player, passing from top to bottom of the playfield, and then away toward the back of the machine. Alternately, they might rotate forward from the bottom of the machine, moving toward the top of the visible area, and then disappearing toward the back.

Slot ReelsThe Slot Symbols Are Arranged Along the Curved Part of the Reels

On the curved area of each reel are various symbols, sized similarly to each other and arranged at regular intervals. Each regularly spaced location that can contain a symbol is referred to as a “reel stop.” This is because at the conclusion of each spin, the reels come to a halt, or stop, with a certain number of these stops showing to the player.

The various icons displayed on the reel stops determine the payouts. Generally, you need to make combinations of at least three matching symbols in order to score a win with lengthier combinations and high-value icons paying more. Each round costs a certain amount in either play chips or real money, so the chance of making a big score is counterbalanced by the costs inherent in playing.

Play for Free

Money Not Needed

If you aren’t yet accustomed to real money slots, then it might be wise to start out with free slots online. Many of the leading slots casinos online provide a practice mode where you can try out the games for play money chips. Several slot developers, including BetSoft and Rival, also allow you to play demo versions of their titles on their websites.

Additionally, there are many so-called “social casinos,” like House of Fun and Caesars Slots, that use a “freemium” model. At these sites, which are usually mobile apps, you get a certain number of complimentary chips to play free online slots. Should you lose all these free chips, there are frequent opportunities to reload without paying anything, but if you’re impatient, you can also purchase chips although they have no real world value.

Of course, by playing with nothing at stake, you lose quite a bit of the thrill of slot games online. Therefore, you will sooner or later want to take the plunge and begin to play slots online for real money.

Play for Real

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When it comes to online slots, real money is where it's at. With top prizes denominated in the hundreds of thousands or even millions of dollars, there's the potential for life-changing money to fall into your hands. You don't need to head to Vegas; slots online bring the full Sin City experience right to your computer or smartphone!

While there are a variety of methods you can use to fund your online casino accounts, we recommend Bitcoin for the best online slots real money experience. Bitcoin allows a broad range of transaction amounts, speedy processing, and low fees. These advantages pertain not only to BTC deposits but also to withdrawals as well. To learn more about Bitcoin and its benefits for online gaming, check out this thorough guide to getting started with Bitcoin.

The reputability and integrity of online casinos ranges from the shady and unscrupulous to the upright and honest. It can be difficult to differentiate between the two. Fortunately, we have identified some of the most dependable real money slots casinos online, and you can learn all about them in our rundown of the most trusted online casinos for USA players.

Slot Machine Features


Over the years, the field of online slots has undergone significant change. Programmers are always coming up with new elements and features designed to make their creations more captivating and alluring. Still, there are some features that have become commonplace, and we have explanations of them below.

Reel Structures

The number of reels involved in a slot and the number of stop positions displayed at once are all variable. The simplest slots have just three reels showing one position apiece, meaning that the user will only see three symbols at once from which to make a winning combo.

The standard video slot today has five reels with three symbols showing on each reel at the same time. There are thus 15 images displayed on the screen at once. Another popular reel structure has three reels with three spots apiece for a total of nine icons simultaneously visible

A Night With Cleo ScreenshotA Night With Cleo Is an Example of a Slot With a 5 x 3 Reel Structure

Other uncommon reel arrangements can be found, such as 5 x 4 or 6 x 3. Some slots eschew the entire idea of reels, instead treating each visible symbol as its own entity rather than as a position on a reel. This philosophy is especially true of “match 3” slots: These games feature large playfields, and any three matching adjacent icons trigger a win, like in the famous non-gambling titles, “Bejeweled” and “Candy Crush.”


The idea of a payline is intimately connected with the reel structure of a slot. As we have seen, in a typical 5 x 3 modern slot, there are 15 symbols on the screen at once. The paylines are the ways of reading these symbols to determine winning combinations.

Using a 5 x 3 slot as an example, you might read left to right across the middle to determine wins. Also, the top and bottom lines can be analyzed in the same way. Going from right to left instead of left to right provides another way of combining the symbols. Two “V” shaped lines can be formed going from the top-left to bottom-middle to top-right and bottom-left to top-middle and bottom-right. Other zigzag-shaped lines are possible.

Fast & Sexy PaylinesVisualization of the Paylines in the Fast & Sexy Slot

You will generally see slot machines with between 9 and 50 lines, but this is just a rough guideline. Other slots have as few as 1 line or as many as 100. Generally, the lines begin at the left and continue right, but sometimes, there are lines that run in the opposite direction, both directions at once, or “partial” lines the are active across the three middle reels while ignoring the first and last reel.

Each line is considered independently when evaluating wins. The highest-paying combination across each line is added to the wins (if any) on the other lines to determine the final payout for a spin. Remember, most lines read from left to right, so you need to line up matching symbols from left to right without interruption on a line in order to have a valid, paying combo. Usually you need three or more consecutive matching images to score a win, but sometimes just two is enough.

Nowadays, there are some video slots that bill themselves as “All Ways,” which means that any combination of enough winnings symbols on consecutive reels generates a win regardless of paylines. On a 5 x 3 slot, there are 243 ways of fitting symbols across the stops on the five reels to make a winning arrangement, so these slots are sometimes called “243-ways” games. Other reel structures lead to a different number of winning ways.

On some slots, you can elect to have fewer than the maximum possible number of paylines active. On others, you must play on all possible lines.


Key to the entire endeavor of playing slots for real money is the amount you can bet with each spin. Most slots let you choose the size of each coin ($0.01, $0.02, $0.05, $0.10, et cetera) and the number of coins per line (perhaps from 1 – 10). It's also sometimes possible to select the number of lines you wish to play.

Your total bet is equal to the coin size times the coins/line times the number of paylines. For instance, on a 25-line slot with a $0.05 coin size and five coins per line, you will be risking (25 x $0.05 x 5) = $6.25 per spin.

By fiddling with these settings, you can usually choose to wager sub-dollar amounts up to more than $20 per spin. It is becoming increasingly common for slots to abstract away the entire coins/size/lines model by having you simply select the total amount you want to bet without making you worry about the details.

Selecting Your BetMost Slots Let You Choose the Coin Size, Number of Coins, and Sometimes Paylines

Wild Symbols

A wild symbol substitutes for any basic symbol to form winning lines. If a wild position qualifies for multiple lines, then it can substitute for more than one symbol simultaneously depending upon which icons are needed on separate lines to make a win.

Often, combos that include wilds multiply the winning amount by a certain value typically 2x or 3x. The wild symbol itself may be listed as a winning image, meaning that three wilds or more in a row have payouts associated with them, which tend to be higher than the wins for any other symbol.

Some wilds appear stacked – that is, several of them occupy adjacent reel stops, meaning that there's a large probability of more than one of them showing up on the same reel at the end of a spin. Additionally, a slot may feature expanding wilds whereby any wild that appears will expand to fill the entire reel, increasing the likelihood of making paying combos.


Scatter icons are an exception to the rule that winning symbols must line up consecutively on a payline in order to count as a winning sequence. Scatters pay out as long as a sufficient number of them are present anywhere on the reels.

In addition to awarding a payment for appearing onscreen, scatters are often the trigger for free spins or bonus rounds (discussed below).

Free Spins

Free spins are granted by meeting the stated conditions for obtaining them. This is generally tied to a specific number of scatters appearing during the base game. In some cases, the more scatters that show up at the same time, the more free spins granted.

During free spins, no money is charged for spinning the reels. The current betsize is carried over from the main game for the purposes of calculating the awards for winning paylines, but it costs the player nothing to participate in these spins.

Additional benefits may apply during free spins, such as a multiplier on all wins, extra wilds added to the reels, or a special set of bonus reels that lead to more frequent winning combinations. It may be possible to retrigger free spins by a sufficient number of scatter symbols appearing within them.

Bonus Rounds

Bonus rounds are usually activated by the scatter symbol or by some other special icon appearing. The formats of these bonus rounds differ quite a bit from slot to slot and are really only limited by the imagination of the creator. Generally, however, they involve the opportunity to pick up random prizes.

Slot Bonus GameThe Bonus Round in Paddy's Lucky Forest Prompts You to Choose One of Three Pots
Each One Reveals a Different Randomized Prize

You might have to select from unopened treasure chests, pick from amongst valuable jewels, or choose to go left or right in a labyrinth. Select wisely, and you will be rewarded with a randomized amount of cash. Choose unwisely, and you'll get nothing and maybe even end the bonus round prematurely.

Progressive Jackpots

A progressive jackpot starts at a fairly low figure, maybe a few hundred dollars. With every dollar played on the machine, however, a small fraction – say a cent or two – is added to the jackpot pool. After enough time has elapsed, a progressive can reach truly breathtaking amounts: sometimes in excess of $1 million!

To win the jackpot, you might be required to hit five of the top-paying symbol. Other jackpots can be awarded randomly after any spin. Once the jackpot is hit, its value is reset back to a low starting figure.

Some progressive jackpots feature money pooled together by many participating casinos. This allows each of them to provide their customers with truly remarkable jackpot totals without having to put up the entire prize pool alone.

Help Screens

With all the special features and ways to win embedded in today's slot machines, many players find themselves wondering what they're looking at when they sit down to try a new game. Fortunately, help is at hand. Virtually every machine created in recent years contains a set of informational screens that explains how the paylines are arranged, what and how many matching symbols you need to achieve the stated payouts, how to activate and play the bonus games, and more.

Look for a button marked “help” or with a question mark or “i” icon. Pressing it will bring up a ton of information to familiarize yourself with the game.

Stampede Help WindowThe Help Screen for the Stampede Slot

Play Slots Online for Real Money

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Now that you know all about slot machines online and what to expect from them, it might be time to start playing yourself. Click the button below to find a reputable casino from among our list and begin your online slot adventure.

History of Slot Machines

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The first slot machine is widely acknowledged to have been invented by California-based automobile mechanic Charley Fey in or around 1895. There had been similar previous machines, but his was the first that could identify winning combinations itself, used a slot for coin insertion, and handled the payouts automatically. Earlier machines depended upon a human looking at the gamefield to determine if a payout was due.

Fey's machine had symbols for three card suits (hearts, diamonds, spades), horseshoes, and an image of the Liberty Bell, leading to the name of this slot: Liberty Bell. Landing three Bells on the reels awarded the jackpot.

Liberty Bell SlotLiberty Bell, Widely Acknowledged as the First Slot Machine

Fey hesitated in patenting his invention, which meant that imitators soon appeared by the dozen. One of the notable early slots was the “Operator Bell” by Mills, which added the fruit symbols and bars that would soon become a staple of slot gaming. Legend has it that as real money play on these machines became banned in various jurisdictions, the fruit symbols and bars became codes for the prizes that could be won in lieu of money: differently flavored candy and packs of gum.

All of these early machines operated along similar principles. The customers put a coin in a slot designated for this purpose (hence the name “slot machine”) and then pulled on a lever. The unit contained a hopper filled with coins, allowing it to dispense payouts without the need for an attendant (unless a huge jackpot was won). Slots continued in this same vein for many decades, increasing in popularity especially after gambling was legalized in Nevada in 1931.

In 1953, Australian slot manufacturer Aristocrat introduced multi-line gameplay with its Clubmaster machine. However, the industry would have to await the development of slots with true video screens before multi-line slots became widespread.

The next major development in the field came in 1964 with the “Money Honey” game by Bally. This was the first electro-mechanical slot machine although the “electro” part of its operations seems to have been restricted to illuminating certain display elements. Still, this marked a departure from previous unpowered slots that relied upon purely mechanical means for their proper functioning.

In 1976 came the “Fortune Coin” machine by Walt Fraley who connected a Sony Trinitron color screen with circuit boards to produce the first video slot. There were no physical reels; the results were instead determined by an RNG: an industry first. It was met with skepticism by the gambling public, which believed that a lack of physical reels meant that the device could be easily rigged against them.

In 1986, the first slot with a wide-area progressive jackpot was released, Megabucks by IGT. This slot, still popular today, is found in casinos all across Nevada with players across the state contending for and contributing to the same jackpot pool. It has since spread to other states, but likely for legal reasons, each state has its own jackpot separate from the others.

WMS Industries in 1996 came up with the concept of a slots bonus game. When this feature was triggered in the “Reel 'Em” title, play moved to an entirely separate game field, and then when the bonus was over, the familiar reel setup came back to the fore.

The mid-90s also saw the first internet casinos pop up, led by InterCasino and The Gaming Club. Microgaming was one of the first firms that started developing online casino software, and it is a name that continues in this field to the present day.

Since the time that slots first arrived on the scene, several developments in the payments department have made them more flexible. One of these was the bill acceptor, which enabled higher denominations, like $1 slots. The second was a credit tracker, which let players carry their winning balances forward to use on future spins rather than having to collect and reinsert a bunch of coins every few rounds.

Borgata Slot VoucherA Slot Voucher From the Borgata Casino in Atlantic City

The final piece of the pay-in/pay-out puzzle came in the 2000s with the development of the TITO (ticket-in, ticket-out) system. This saw all the coins abstracted away into printed slips containing barcodes representing dollar amounts. Players can still insert currency bills into the machines to initially fund their sessions, but then all winnings (except jackpot handpays) are issued in the form of TITO tickets. These vouchers can then be inserted into the same machine or a different one later on, and the credit balance is transferred. When ready, the customer can visit the cashier or a redemption machine to have a ticket converted into real cash money.

Differences Between Live and Online Slots


Truth to tell, there's now hardly any difference between the most innovative slots in a physical casino and those that are found online. The proliferation of video displays, multi-line machines, and TITO mechanisms in brick-and-mortar games means that offline slots have been becoming more and more like their online counterparts.

In some areas, like immersive multi-channel sound effects and 3D displays, the most modern offline slots may even hold the edge over their peers on the internet. Of course, online slots offer greater convenience because you don't have to leave the house, and you generally have a larger array of slots to choose from online except perhaps in the grandest and most palatial live casinos.

While a few slots online must be played via download on a traditional PC, a majority of them are now accessible on the web, including on mobile devices, with no download required. You can therefore load them up and enjoy a few spins whenever you feel like it on whatever system you happen to be using at the moment!

Reviews of Slots Games

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We understand that there are tons of slots online for you to play, and you might feel a bit overwhelmed at first. Therefore, we have prepared complete reviews of some of the leading titles. Read them below to get an idea of what a slot is about before beginning to play.