For an underdog, the equation is 100/(odds +100) x 100. So a +150 underdog would be calculated as 100/(150 + 100) x 100. That equals 40, meaning a +150 underdog has an implied win probability of 40 percent. For fractional odds, the equation is denominator/(denominator + numerator) x 100.
The math behind calculating payouts on sports bets\n\n When the odds are negative, change the number to positive and use this formula: 100/Odds * Stake = Profit. When the odds are positive: Odds/100 * Stake = Profit.