# What player rating system can I use when the rating can only get larger?

I am developing a turn-based multiplayer app (2 players per match) for Android. As backend I use Google Play Game Services. I have implemented a leaderboard. Now I consider how to design the ranking system - I just realized that Leaderboards in Play Games Services only support increasing existing scores but not decreasing them. Of course that means that I cannot use the Elo system.

Are there good rating systems that only take into account the current scores of both players and do not decrease the score of the user losing the game? The new score of the winning player should be the higher when he was much worse than his opponent and vice versa. I know, that it means there will be inflation :(.

• To clarify for the close votes: this question isn't asking about which technology to use, but about the design of a scoring/ranking mechanic with particular criteria. I would consider this on-topic. For the asker: giving the winner a number of points proportional to max(opponentLevel - myLevel, minimum_increase) (and 0 for the loser) would satisfy your criteria: scores only stay the same or increase, and they increase more when a low-ranked player beats a higher-ranked one. Do you have any additional criteria we can apply to determine whether this is a good fit for your situation? – DMGregory Apr 10 '16 at 16:17
• Thanks for your answer @DMGregory. The formula you proposed definitely goes in the direction I had in mind. It would be even better if it would not be linear but some kind of logarithmic such that a too big difference in the scores of the players before their match does not lead to a huge increase in score for the weaker player in case he wins. So my question is aiming for whether there are well kown scoring systems already where scores can only get larger. If not I would of course have to think about a formula myself – Max Apr 10 '16 at 19:06