Convert a ratio to a percentage as a favorite

For example, 2:1 - this means you should expect to win two times for every one loss, or alternately, you will win 2/3 times. 2/3 is 66%

Add the left side to the right side and divide it by the number of wins.

2 (wins) / 1+2 = 2/3 = .6666

Convert a ratio to a percentage as a dog
Wins / left side + right side

For example, if you're a 4:1 dog that means you lose 4 times and win 1 time.

1 (win) / 4 (losses) + 1 (Win) =1/5 = 20%