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Not a programming question but game development related.

I am creating an iPhone online game which I wish to be free-to-play where in-app purchase is used for monetization. The important point is to make sure that this does not break the game-play, my priority is gameplay first, monetization second.

One popular way of monetizing the player base is to sell your in-game currency, however there are 2 ways to go about this:

  1. One Currency: This currency can buy anything within the game, it can be earned through normal play at a limited rate. Players can, however, choose to buy this currency directly to speed up the acquisition of the currency.

  2. Dual Currency: One currency can be earned through normal play and it can be used to buy a limited set of items that is required for normal enjoyment of the game. The second currency is 'premium' and must be purchased using real world money. This second currency can be used to purchase 'premium items' that gives extra abilities such as increase EXP gain, etc. The 2 currencies can be traded between players to give non-paying players to exchange their time for the 'premium' currency.

Both methods do not break gameplay and allows players who does not wish to pay enjoy the entire contents of the game if they put in enough time and effort.

My question is, is there any reason why you would pick one over another? What are the pros and cons that I should pay attention to when implementing each alternative?

Thank you.

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I think with one currency players tend to ask themselves, why would I pay if it won't give me anything special in return. Why pay for something if I can get it by playing a lot. –  Thomas Feb 23 '12 at 7:58
I believe that there are evidence (can't recall a specific link) that players that think this way would not pay for your premium currency anyways, also the "buy more money" mentality is meant to target time-poor and money-rich players as they cannot commit as much time to grind for money. –  Jamornh Feb 23 '12 at 9:23
If you're interested, you can look at League of Legends as an example of a successful dual currency model. –  João Portela Feb 23 '12 at 13:58

3 Answers 3

up vote 5 down vote accepted

Using one currency has the benefit of keeping things simple. You don't require dual prices for anything, and you don't require trading to give all players potential access to all content.

The psychology of the two approaches is complicated. I'm going to look at this from the commercial point of view. People fall into (at least) the following categories:

  • "Paying players get an advantage? I'm not playing". (You can ignore these)
  • I will pay a small amount to get things I would have got anyway as a money-time tradeoff. (Favour single currency)
  • I won't pay, but I will only play single-currency games (time-money tradeoff). Whether you care about these players or not depends on your gameplay, and the nature of interaction between players.
  • I will pay to get the best stuff and then lord it over the non-paying plebs. (Slightly favour dual-currency).
  • I'll play for a bit before I make up my mind. These players don't have a fixed approach to money-time tradeoffs, so they could go either way.

I'm not sure what research has been done on the relevant sizes of the camps, and it may well depend on the genre.

Additional considerations:

  1. Having two currencies makes it more complicated. Not only does it complicate the code, but it complicates the balancing, and keeping the economy balanced is a familiar problem to MMO designers.
  2. There is actually a third way. I'm currently playing a game which has two currencies; one of them is for sale, but even non-paying players acquire it very slowly (one coin some of the time on level up). Some items are only for sale in the monetised currency; others have prices in both.
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Wouldn't the third way give you the drawbacks from both sides and not much of the up side? If all players earn for-pay currencies anyway why not just have 1 currency? You'd end up complicating the code due to having 2 currencies as well. –  Jamornh Feb 23 '12 at 9:20
@Jamornh, it gives you roughly the same pros and cons as dual-currency but you'll lose fewer of the third group (free players who get upset at not having theoretical access to absolutely everything). –  Peter Taylor Feb 23 '12 at 9:54
After looking around there is an interesting argument for dual currency: inflation. With 2 currencies, you can allow inflation to occur in the first currency (earned easily in game thus supply of the currency naturally increases over time) while in the second currency, inflation is controlled as players only buy currency to purchase something and it is removed from the system. Do you have any thoughts on the benefits of this? –  Jamornh Feb 27 '12 at 7:46

The best approach I've seen as of yet is that of Spiral Knights.

There are two currencies, and they do completely different things.

You cannot use a currency instead of the other to do something, and that's good because that would defeat the purpose of having two currencies in the first place!

You use crowns to buy stuff, you use energy to revive yourself and other people, and to go deeper in the dungeons, and you use both (not either! both!) to craft items.

Crowns are dropped by mobs, energy can be bought with real money, and every player has 100 "free" energy which automatically slowly recharges in 22h. Of course this free energy is spent before the other one. Many things cost more than 100 energy so in that case you have to use paid energy to do that.

Of course there's an exchange for the users to trade crowns for energy and vice-versa.

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While it's an interesting data point, it doesn't really go into why choosing a system like that is a good thing, whether it would help for monetization, that kind of thing. –  Tetrad Feb 23 '12 at 16:33
@Tetrad: I'm sorry, I will elaborate if I find the time to. –  Lohoris Feb 23 '12 at 16:48

Basically you should create a game play that any player can enjoy the most, either way the only people who has money and willing to spend it without much hesitation, will buy any thing from you and others will not that often.

And only from these people you will get your main portion of revenue, while from others you will get about 10-15% purely depending on your game. So you can implement either one it does not make any difference to the player or you.

The only problem you will face is how to implement any one in your game.

I have seen both kinds of game with nice game play get users to buy from the apples app store after playing the game.

Here is an example for both.

1.. Dual Currency :- You will find this game called steam birds one of the kind that implements dual money kind of a thing in the game. If can pay then you will be rewarded by some new planes which has got extra speed and power. It is also available on the iphone.


It has a simple but really awesome game play that makes the user to stick to the game day and night.

2.. One Type Currency :- If you ever owned an iphone or working on udk then you will know this game. Its called Infinity Blade.


If you look at the above page then you will get an idea about how good and famous that game is. The link shows that the top in-app purchase is about $50, so can see how people spend there money if they like the game.

So in the end it comes down to how much work are you putting in the game for its look & feel, then you can get as many bucks as you want by implementing the anyone of the above 2 methods.

I hope this helps you even a bit for your game.

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