The following table shows what the probability of beating an opponent is based on the difference in rating points.
Rating diff = difference between your opponent's rating and yours
Prob win = probability of winning
The left column is the difference between your opponent's rating and your own. +100 means that your opponent
is rated 100 points higher than you. In this case, you have a 35.99% chance of winning. If your opponent is rated the same,
then of course the probability of winning is 50%.
Note that even if you are rated 200 points higher than your opponent, the probability of winning is 76%, which means that you
are expected to lose the game one out of every four times you face such an opponent.
Note: This is often the way this table is used (probability of win), but it is actually more accurate to say that the percentage
is your expected score against an opponent. In others words, 50%, or 0.5 is often seen as the probability of beating an opponent, but
it is actually your expected score against an equal rated opponent over time.