Definition
An underdog is the side expected to lose a game or event. In betting markets, the underdog is usually shown with plus odds, such as +150 or +220, because the payout is larger than the amount risked.
For positive American odds, the profit formula is:
Profit = Stake × (Odds / 100)
A $100 bet at +150 returns $150 in profit, plus the original $100 stake.
Worked Example
If the Giants are +180 against the Eagles, the Giants are the underdog. A $50 bet at +180 would profit:
$50 × (180 / 100) = $90
If the Giants win, the sportsbook pays $90 in profit and returns the $50 stake, for a total payout of $140. If the Giants lose, the bettor loses the $50 stake.
Why It Matters
Underdogs matter because plus odds can create value when a bettor’s projected win probability is higher than the market’s implied probability. At +180, the break-even probability is 100 / (180 + 100) = 35.71%, so the bet needs to win more often than that before considering sportsbook hold.