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.

  • 1
    \$\begingroup\$ 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. \$\endgroup\$
    – Thomas
    Commented Feb 23, 2012 at 7:58
  • 3
    \$\begingroup\$ 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. \$\endgroup\$
    – Jamornh
    Commented Feb 23, 2012 at 9:23
  • 1
    \$\begingroup\$ If you're interested, you can look at League of Legends as an example of a successful dual currency model. \$\endgroup\$ Commented Feb 23, 2012 at 13:58

4 Answers 4


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.
  • \$\begingroup\$ 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. \$\endgroup\$
    – Jamornh
    Commented Feb 23, 2012 at 9:20
  • 1
    \$\begingroup\$ @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). \$\endgroup\$ Commented Feb 23, 2012 at 9:54
  • \$\begingroup\$ 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? \$\endgroup\$
    – Jamornh
    Commented Feb 27, 2012 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.

  • 1
    \$\begingroup\$ 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. \$\endgroup\$
    – Tetrad
    Commented Feb 23, 2012 at 16:33
  • \$\begingroup\$ @Tetrad: I'm sorry, I will elaborate if I find the time to. \$\endgroup\$
    – o0'.
    Commented Feb 23, 2012 at 16:48

Having a single currency is not simple at all for monetization. This is because you would have to implement many efficient money sinks in the game to stop players from grinding their way to unlocking all content/items. Without good sinks, there is no incentive to buy IAPs. I suppose in terms of coding it might be slightly more complicated, but with a single-currency model you'll forever have to be hyper-alert to the in-game economy's fine-tuning to make any money, as well as be a whiz at implementing the right balance of currency source vs. sink. Remember, too effective a sink and players just avoid that feature of a game altogether. Basically, you'll have to be a godlike economist as well as a brilliant coder and game designer (or hire all three).

There is a good reason why all the top grossing F2P games currently - Supercell's games, Zynga's games, League of Legends, etc. - use a dual currency model. It's actually a lot simpler in the long run, and has some psychological benefits to boot (e.g. the sunk cost effect, where unused premium currency sits in your inventory, a constant reminder that you could use it if you bought a little more). You can allow people who like to grind, grind their hearts out on the soft currency. And you can keep the premium currency exclusive to payment. You can gift it slowly to reward loyalty and improve your KPIs (retention, re-engagement), but you control the flow of this currency tightly.

In the end, it does come down to the type of game you're making. Some games are more suited for a single currency, others require more (I've seen games with 5 currencies). However, you should probably default with dual currency model and have a damn good reason for not using it if you do otherwise. If you go with a single currency, there's a good chance you'll have a hard time making any revenue.

Strongly recommended reading: Mobile & Social Game Design: Monetization Methods and Mechanics, Second Edition By Tim Fields, Brandon Cotton

disclaimer: I've worked with game publishers and developers, and am currently a data analyst and monetization specialist for a company that does both.


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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