An underdog is an outcome that the bookmaker does not expect to win. An underdog's outsider status is reflected in the odds that they are assigned.

An underdog is the opposite to a favourite - the outcome that a bookmaker expects to win.

How underdogs are displayed with odds

It is easy to spot an underdog when surveying the odds of a competition. An underdog is always the outcome with the biggest odds, and consequently the odds that will see the biggest returns - which would be expected, given that the outcome is considered unlikely to happen.

Underdogs are displayed differently depending on your odds format preference.

Underdogs with decimal odds

When using decimal odds, the underdog is the outcome with the odds with the greatest numerical value - the odds that are furtherest away from 1.00.

For example, an outcome with odds of 8.40 would be considered a bigger underdog than an outcome with odds of 5.70.

Underdogs with fractional odds

When using fractional odds, the underdog is the outcome with the biggest fraction. If the numerator (the first number) is bigger than the denominator (the second number), then this outcome would be considered an underdog.

For example, odds of 4/1 would be considered the underdog, while odds of 1/4 would be considered the favourite.

Underdogs with American odds

When using American odds, the underdog is displayed using positive odds, while the favourite is displayed with negative odds.

The higher the odds, the more of an outsider the underdog is considered.

For example, an outcome with odds of +500 would be considered a greater underdog than an outcome with odds of +350.

How to use underdogs in sports betting

Backing an underdog is considered a high risk strategy, as outcomes are generally considered underdogs for a reason; they are not expected to win. However, nothing in sport is certain, and underdogs can upset the narrative and defy the odds to win.

Although high risk, backing an underdog does provide high reward if it proves successful due to the higher odds offered. Successfully backing an underdog will see greater returns from a smaller stake.

The key with backing an underdog is to use implied probability to find value in a bet.

For example, if Everton were priced at odds of 2.40 to beat Liverpool at Goodison Park, this gives an Everton victory an implied probability of 41.7%. However, if you consider Everton to be more like 60% likely to win - perhaps due to factors such as their recent form, their home record or injuries to key Liverpool players - then this would be a value bet and an underdog worth backing.

We’re on a mission to educate the world’s betting population through good, honest betting advice, information and tools.

Potential Bets is owned and operated by Bettor Publishing, a registered company in England and Wales. Company number 12103210. Registered address Unit 2.05, 12-18 Hoxton Street, London, N1 6NG. Please bet responsibly. If you think you have a problem or you require assistance, please visit our responsible gambling page.