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Numbers Getting Bigger: What Are Incremental Games, and Why Are They Fun?

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This post is part of a series called Numbers Getting Bigger.
Numbers Getting Bigger: The Design and Math of Incremental Games

Incremental games are fascinating and perplexing. Marked by minimal player agency and periods of inactivity, they seem to defy conventional logic about good game design, and yet nonetheless have attracted a substantial player base. Let's examine them in more detail, and see if we can explore why that is.

What is an Incremental Game?

You click a button, a number goes up. You click it again, the number goes up again. You keep clicking, and eventually unlock something that makes the number go up for you. Now the number keeps going up, even when you're not playing. Next, you repeat this process, forever.

That, in essence, is the framework of an "incremental" game. While they may seem simple, even brutally so, there is a depth of play and surprising addictiveness to them. They appeal to a variety of playstyles as well, and there have been successful commercial and casual incremental games like Clicker Heroes and AdVenture Capitalist, as well as more experimental or hardcore examples like Candy Box, Cookie Clicker and Sandcastle Builder.

CookieClicker by OrteilCookieClicker by OrteilCookieClicker by Orteil
In Cookie Clicker, it's all uphill from here.

So what defines an incremental game? Though there is substantial variation and experimentation in the genre, the fundamental aspects of the design are the following:

  1. the presence of at least one currency or number,
  2. which increases at a set rate, with no or minimal effort,
  3. and which can be expended to increase the rate or speed at which it increases.

It's that loop of accumulation, reinvestment, and acceleration that defines the genre and distinguishes it from games that merely have an increasing score. As an example, in the influential Cookie Clicker, the player seeks to amass 'cookies', which they initially increase by clicking a giant cookie, and then spend to buy upgrades which produce more cookies.

One of the distinguishing features of these games is that the number can increase without the player's direct involvement or even presence. This has led some to call incremental games "idle games," since they can be left to run and then returned to. While this is an important feature, I don't think its central to what defines these games or why players enjoy them. The unending upward growth of numbers is the most prominent feature, and so "incremental game" is a more useful title.

The Psychology of Increasing Numbers

What is it about these games that can inspire such dedicated play? There are a number of reasons, including two important ways that incremental games leverage unique facets of human psychology.

The first is a term that is commonly brought up in the discussion of incremental games: the "Skinner Box." Named (to his chagrin) after the behaviorist B. F. Skinner, these were experimental chambers he built to study behavioral conditioning of animal subjects. The "operant conditioning chamber" would typically house an animal participant who could produce a reward (like food) in response to performing an action (like pushing a button). Notably, once the response mechanism has been learned, animals have been observed to repeat the food-producing action even if it only produces a reward after long intervals or even at random.

By analogy, systems that periodically reward users or players for repetitive tasks are often derisively called Skinner Boxes, because the neurological feedback loop this creates can be incredibly addicting. This structure is certainly quite apparent in incremental games: The player performs an action like clicking or waiting, and is periodically rewarded for their efforts by a number going up. This isn't necessarily bad in and of itself, and is actually a quite commonly used mechanic. Many games need to train their players to perform certain actions in the game system, and use positive rewards (points, experience) and negative outcomes (death) to teach the player the correct way to proceed. In incremental games the usage is simply more obvious.

The second psychological underpinning of incremental games is our accumulation desire and loss aversion. Our brains are wired to dislike losing things we have, and, conversely, to give us a strong desire to accumulate things. 

Incremental games work with both sides of this. Because the primary currency always goes up even when you're not playing, it reduces the anxiety caused by loss aversion: you can safely do something else for awhile without the stress of the currency going away. Additionally, coupled with our brains' poor numeracy skills, we can enjoy numbers that go up, even if those numbers lack external meaning. So, although it can seem ridiculous, a number that simply goes up can actually make us feel good. 

Again, this is laid bare in an incremental game, but most games take advantage of this to some degree: it's why a "score" is such a widespread mechanism for player reward.

Clash of Clanss storage cap uses loss aversion You lose potential gains unless you check in frequentlyClash of Clanss storage cap uses loss aversion You lose potential gains unless you check in frequentlyClash of Clanss storage cap uses loss aversion You lose potential gains unless you check in frequently
The storage cap in Clash of Clans uses loss aversion: you "lose" potential gains unless you check in frequently.

Origins of the Genre

Some of the earliest uses of the incremental mechanic were amongst the first generation of MMOs in the late 1990s. Because MMOs used a subscription model, they needed to entice players to play for as long as possible. Part of how they accomplished this was with vast persistent worlds and complex social systems, but another technique was setting players up on a sort of "treadmill" of power: you kill a few rats, you gain a level! You kill more rats, and gain another. Now rats don't give enough experience, so you move on to killing slimes, and so on. The player is always running for the next goal, but they never actually get anywhere. 

There's a strong work/reward loop in that mechanism, and, critically, the time invested to reach each additional reward takes incrementally longer and longer. EverQuest was particularly famous for its level-grinding, the leveling curve of which was so steep that players actually became relatively less powerful the more they played. Despite that, the reward loop the game reinforced could be extremely seductive, and it was one of the first games to propel games addiction into popular discussion.

Lampooning this endless grind was 2002's Progress Quest by Eric Fredricksen, which might be the first example of a true incremental game (as opposed to just using the incremental mechanic as a hook as EverQuest does). It's also among the most minimalist, as it eliminates any semblance of player interaction. It is a 0-player game: once you roll your character, the game will have them kill mobs, complete quests, and level up, without any further input from you. Despite being an almost literal reductio ad absurdum, critics have noted that it was "something much more frightening: it was enjoyable."

Progress Quest by Eric FredricksenProgress Quest by Eric FredricksenProgress Quest by Eric Fredricksen
Some of the increasing progress bars in ProgressQuest.

Some years later, social games would be the next inheritor of the incremental mechanic. Played primarily on Facebook, social games similarly needed players to play for as long as possible (though they didn't use subscriptions, but rather the emerging pricing tools of "free"-to-play). Notably, the incremental mechanic became not only the reward system of these games, but often the entire game itself. One of the most successful of these was 2009's FarmVille. It was ostensibly a farming simulator, but contained very little resource management or strategic decision making. Instead, the player buys plots of land on which to grow crops (and later, breed livestock), which can later be harvested and sold, and then the proceeds of which can be used to buy additional plots, and so on ad infinitum.  At its height, it was played by an astonishing 80 million people.

Farmville by ZyngaFarmville by ZyngaFarmville by Zynga

The apparent simplicity of games like FarmVille led the games critic and professor Ian Bogost to produce a satirical deconstruction of the concept with Cow Clicker in 2010. Designed to reveal the starkness of the core underlying play mechanism (clicking a cow, having a number go up), Bogost was instead surprised and dismayed to find people actually played his game, without irony. Though it was an attempt to show how empty and meaningless these games actually are, Cow Clicker inadvertently showed the opposite.

Incremental Games Today

Many of today's most popular mobile games (the modern successors of social games) make use of incremental mechanics. The immensely successful Clash of Clans (2013) is framed as a strategy war game, but the battling mechanic is fairly simplified and only forms a small part of the experience. The main aspect of play is upgrading the village base by spending gold and elixir, both of which accumulate on their own, and can be made to accumulate faster with incremental upgrades. 

Hay Day, made by the same company, is even clearer in its use. The core gameplay loop is exclusively incremental growth and reinvestment:

The game loop in Hay DayThe game loop in Hay DayThe game loop in Hay Day
Hay Day's game loop. Based on a diagram from Game monetization design: Analysis of Hay Day by Pete Koistila.

Of the most successful modern incremental games has been 2013's Cookie Clicker, which has brought more mainstream attention to games focused solely on incremental mechanics. Cookie Clicker uses a single currency (cookies), which the player can slowly accumulate by clicking a large cookie, and then spend on upgrades which produce cookies autonomously. The simple premise, charming art style, and the gradual descent into absurdity of its "plot", all helped propel the game and its genre to widespread popularity. It inspired a wave of similar games, with new takes on the concept continuing to be released today.

Are These Even Games?

Because of the simplicity of their core mechanic and the limited interaction with the system, incremental games can strain our definitions of what a "game" even is. Many critics and commentators have called these games mindless, dumb, and pointless, while at the same time conceding that they can be addictive or hypnotic. Cow Clicker creator Ian Bogost, speaking of Cookie Clicker's monotony and repetitiveness, went so far as to call it among the first game for computers, not people, to play. That seems at odds with the large number of human beings who do play it, though.

Number by Tyler GlaielNumber by Tyler GlaielNumber by Tyler Glaiel
Number by Tyler Glaiel, a particularly stark example.

However they may appear, incremental games are, in fact, games. We can set aside their immense addictive value for a moment, because while that speaks to why we might find them compelling on some level, its not the same as analyzing them as games. Games of most genres appeal to some visceral or subconscious area of their players, but that is secondary to what makes a game a game.

First, incremental games do have some non-obvious mechanics to unpack, most primarily that of discovery. In most incremental games, the player doesn't know the extent of upgrades they can buy, or know the upper bounds of the game's main number or the speed at which it can increase. Exploring the limits of an interactive system is one of the hallmark qualities of how players experience a game, and incremental games are no exception. Even if they appear to be simple, they often permit vast exploration. Candy Box in particular is arguably more about exploration and discovery than it is about incremental growth, despite that being its most obvious feature.

Secondly, while incremental games lay bare the vapidity of their premise ("make a number go up a lot"), it's the means to that end that can actually be engaging. Cookie Clicker, for instance, does permit the use of strategy because there are multiple ways the player can increase their "Cookies per second" metric. So the "game" is about optimizing the system in pursuit of that goal. Most games actually have meaningless goals ("make this score go up") but it's the pursuit of them that's the fun part. Incremental games are just startlingly upfront about this convention.

In his seminal 1937 work Homo Ludens, the anthropologist Johan Huizinga observed of play that it was "not serious, but at the same time absorbing the player intensely and utterly. It is an activity connected with no material interest, and no profit can be gained by it." Those are qualities that we can observe quite readily in incremental games.

Beauty in Simplicity

Incremental games have seen a surge of interest in recent years, and we'll undoubtedly continue to see new examples, further exploration of the mechanic, and innovations on the premise. It would be a mistake to dismiss these games as merely inexplicably addicting. 

I hope that by giving them a critical examination and by looking through their history, that we can come to appreciate their minimalist beauty and elegant execution. So keep an open mind and explore the form a little, and don't be surprised if you lose a few hours in the process.

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