The formula for determining one’s advantage (or disadvantage) on any given wager, is as follows: winning percentage x (average winning odds + 1.0). So that when you have a 40% win expectation and average winning odds of 2-1, this becomes .40 x 3 = 1.20 over 1.0, or 20 per cent overlay. Your bet thus becomes a multiple or a fraction of the number
20 (according to the size of your bankroll). If your overlay advantage were 10 %, you would then wager by betting a multiple or a fraction of the number 10.