The regular elo formula is complicated.

The most basic elo formula is win = 1 points, draw = 0, lose = -1. Which is a little too basic.

I looked around and couldn't find a 'medium difficulty' elo formula. Anyone have a medium difficulty proposal?

Regular elo formula:

The Elo rating system embodies this by using a formula that changes a player's rating by adding K(S-E) to his rating each time. K is a constant that is the same for all players; the higher it is, the more easily your rating changes. S is the score of the player in a match (+1 for a win, 0 for a loss). E is the expected score of the player in the match. Against a weak player, it is close to 1 since you expect a strong player to beat a weak player most of the time. Conversely, against a stronger player, it is close to 0. You can calculate E using the formula E_A = 1/(1+10(R_B-R_A/400)), where E_A is the expect score of player A with rating R_A when faced with player B with rating R_B.