What is an underdog in betting?
The underdog is the team or player that the odds rate as less likely to win an event, which is why a winning bet on the underdog pays more than one on the favourite.
In any two-sided contest, one side is the favourite and the other is the underdog. Americans shorten it to “the dog”. British racing prefers “outsider”. A really big-priced underdog is a longshot.
Spotting one:
- Decimal: the bigger number (4.50 against 1.22).
- Fractional: the bigger fraction (7/2 against 2/9).
- American: the plus sign (+350). On a point spread, the underdog is the side getting points (+6.5).
Example
A tennis match: Player A is 1.22, Player B is 4.50 (+350).
- Player B’s implied chance: 1 ÷ 4.50 = 22.2%
- A $20 bet on Player B returns $90, a $70 profit.
- A $20 bet on Player A returns $24.40, a $4.40 profit.
So the underdog needs to win only about one match in four and a half for the bet to break even. The favourite has to win more than four out of five.
With a spread, the underdog doesn’t even have to win. An NFL team at +6.5 covers if they lose by six or fewer.
Watch out
There’s a romantic idea that backing underdogs is the smart, contrarian play. It isn’t, automatically. And backing favourites isn’t “safe” either. The only question that matters is whether the price is bigger than the real chance deserves. That’s a value bet, and it can sit on either side.
Two honest notes from experience:
- Underdog betting is streaky. You’ll lose most of your bets and rely on the winners being big enough. Plenty of people can’t stomach eight losers in a row, even when the maths is fine. Keep stakes small and steady.
- Casual money piles onto famous favourites. That can leave the underdog’s price slightly better than it should be, especially in big televised games. “Can”, not “does”. You still have to do the work.