To calculate your potential payout on an underdog, all you need to do is multiply your stakes (the amount of money you wagered) by the value resulting from the moneyline odds divided by 100. Put simply: Potential profit = Wager x (Odds/100).
To convert from a probability to odds, divide the probability by one minus that probability. So if the probability is 10% or 0.10 , then the odds are 0.1/0.9 or '1 to 9' or 0.111. To convert from odds to a probability, divide the odds by one plus the odds.
