Sports Betting 101: Betting The Underdog

The majority of games in pro and college sports will have a favorite and an underdog. The betting odds will also reflect this overall perception of the matchup.

Underdogs can sometimes be easy to identify, such as when a winless squad is getting ready to play an undefeated powerhouse. But there are also times when the difference is much less noticeable.

While the overall concept is simple in nature, there’s more to know in order to understand this basic sports betting term fully.

What’s an underdog in sports betting?

The underdog is the team or individual seen as less likely to win a game. The opponent, then, is the favorite.

  • The Boston Red Sox are underdogs for tonight’s game against the Toronto Blue Jays.
  • The Toronto Blue Jays are favored to win over the Boston Red Sox.

Sports betting odds can point you to the favorite or the underdog in a matchup. The exception comes in matchups that oddsmakers deem too close to call, also known as pick ’ems.

Underdogs can also appear elsewhere in betting discussions:

  • Several of the underdogs look good for the next Kentucky Derby.
  • One of the underdogs could surprise and win the next Super Bowl.

In examples such as these, underdog is generally interchangeable with other terms and phrases like a dark horse or long shot.

How to identify the underdog in a matchup

For the vast majority of games, you can identify favorites and underdogs by their respective betting odds.

Underdogs will have positive moneyline odds and spread numbers, indicating you can win a return of more than the value of your original wager:

  • Moneyline: Cincinnati Bengals +180
  • Spread: Cincinnati Bengals +4.5

The favorite will have negative numbers in both instances:

  • Moneyline: Los Angeles Rams -155
  • Spread: Los Angeles Rams -3

The aforementioned pick ’em games are rare. When this happens, the game is essentially a toss-up with no favorite and no underdog. On the odds board, the values might both be negative, such as -110 on each side.

American betting odds use whole numbers. Other countries and types of betting (like horse betting) may use decimal odds and fractional odds. In both of those cases, the higher of the two values is the underdog.

For individual sports such as tennis or UFC, the same rules apply on betting odds, as there will typically be clear favorites and underdogs for each matchup. When it’s a sport with multiple participants, like a PGA Tour event, there will generally be favorites and long shots to win.

Underdogs for common bets 

In general, game listings at online sportsbooks will start with three standard bets: moneyline, spread and total. The first two will indicate favorites and underdogs for each game.

Moneyline underdogs

TeamMoneyline Odds
San Diego Padres+110
San Francisco Giants-130

In this contest, the San Diego Padres are the underdogs based on the +110 odds on that side. The favored San Francisco Giants are at -130. Another thing to note is that the gap between these numbers can indicate the perceived closeness of the game or can reflect the pricing structure of the sportsbook.

Spread underdogs

On the spread, both sides have their own spread number, as well as an associated odds number.

TeamSpread Odds
Phoenix Suns+1.5 (-110)
Milwaukee Bucks-1.5 (-110)

As above, the positive spread number indicates the underdog in the game. The odds for point spread bets will generally be in a very tight range, almost always -110 is not otherwise indicated. Any difference between the numbers could indicate that one side is attracting more action.

Are there underdogs for other bets?

For non-moneyline and spread bets, the odds can still point us to the underdog or the less-popular choice.

Over/under betting

Bet on how much overall scoring there will be in a game. Sportsbooks will set a line, and you can wager whether the actual total score will be over or under it:

Seattle Kraken at Vegas Golden Knights, total goals

  • Over 5.5 -115
  • Under 5.5 -105

For the most part, over/under odds will start at around -110 on both sides. The odds can then shift in response to betting action. At this split of -115/-105, can we figure out which side of the bet is the favorite?

We can get a more favorable return on the under at odds of -105, so we can interpret that to be the underdog here. In other words, the under is the less likely — or the underdog — of the two options, at least as far as the odds are concerned.

Prop betting

Beyond the bets just discussed, props are some of the most popular options on the sports betting menu. Games in each of the major sports will each offer a variety of prop bets, such as the first player to score a basket in an NBA game. In addition to multiple-choice bets like that, you can also bet on props with just two options:

Total passing yards for Aaron Rodgers

  • Over 287.5 (-140)
  • Under 287.5 (+120)

In our example, the line for Aaron Rodgers is 287.5 passing yards. Is one of the outcomes more likely than the other? According to the sportsbook, it’s more likely that Rodgers exceeds 287.5 yards in the air, as that’s the option with negative odds. Rodgers passing for less than 287.5 yards is the underdog.

The same rationale applies to other forms of wagering. For example, a futures bet on the winner of the next NBA Finals would have some favorites on top of the board, followed by the rest of the teams in the league, with long shots, or underdogs, at the bottom.

Understanding the differences between underdogs

In sports betting, you will see slight and massive underdogs with several points in between. For research purposes, you can categorize underdogs based on their odds:

  • Toss-ups: The odds are even or nearly so on both sides, such as -115/-105.
  • Could go either way: Odds for the underdog are +120 or less. There is a favorite in the matchup, but it wouldn’t take too much for the underdog to win.
  • Sizable favorite: The underdog’s odds are between +150 and +300. Anything could happen, but the favorite is likely to win.
  • Mismatch: Odds for the underdog are greater than +300. Barring unforeseen circumstances, the underdog is likely to lose.

By fully understanding the matchup through the lens of betting odds, you’ll begin to get a much clearer picture of the projected difference between favorites and underdogs.

Is betting on underdogs profitable?

On paper, betting on underdogs at positive odds looks like a way to win more money. If you win, you’ll double your money at odds of +100, and the potential returns climb along with the odds.

OddsProfit on a Winning $100 Bet
+100$100
+125$125
+150$150
+175$175
+200$200
+250$250
+300$300
+400$400

As the odds climb, the possible winnings rise along with them. However, that comes with the big warning that while underdogs can certainly still win, but there are no guarantees that they will.

They’re underdogs for a reason, after all. For underdog betting, it’s important to understand that the potential return is higher in exchange for a lower chance of winning the bet.

Are underdog odds always positive?

On occasion, the underdog in a matchup can also have negative odds. For example, the moneyline odds for what appears to be a very tight affair could look something like this:

TeamMoneyline Odds
Kansas City Chiefs-105
Green Bay Packers-115

For this example, the Green Bay Packers are very slight favorites over the Kansas City Chiefs. The potential return on winning bets is a little more attractive on the Kansas City side, but the difference is far from a game-changer.

When the odds for a two-sided bet fall into such a close range, the wager is close to being a toss-up. It’s even possible to see moneyline odds that are exactly the same.

TeamMoneyline Odds
Los Angeles Chargers-110
Denver Broncos-110

When even the sportsbooks are viewing a contest as a toss-up, be sure to factor that into your thinking.

What are the chances of an underdog winning?

At times, betting trends can provide some valuable insight, but they shouldn’t be the sole factor in your wagering decisions. For example, recent trends can continue or reverse themselves, while historical numbers don’t tell the story for an individual year.

To demonstrate, here are the betting records for closing-line underdogs over the last five NFL seasons, both on the moneyline and against the spread.

SeasonMoneylineATS
202198-171 (36.4%)139-128-3 (52.1%)
202083-172 (32.5%)141-114-1 (55.3%)
201991-164 (35.7%)133-113-10 (54.1%)
201885-169 (33.5%)133-115-8 (53.6%)
201774-179 (29.2%)113-132-8 (46.1%)

Data such as this can give you some broad context to consider. To gain more insight into what might happen, you can look to the betting odds to help determine the possibilities. You can use the following formulas to determine the implied probability of an outcome based on the numbers.

Positive odds: 100/(Odds+100) * 100 = implied probability in percentage form

For example, odds of +200

100/(200+100) * 100 = 33.33%

Negative odds: Odds/(Odds+100) * 100 = implied probability in percentage form (for the purposes of the formula, change the odds number to positive)

For example, odds of -150

150/(150+100) * 100 = 60%

For additional insight, here is what a few different odds numbers indicate for the probability of victory:

Favorite OddsImplied ProbabilityUnderdog OddsImplied Probability
-13557.45%+11546.51%
-14559.18%+12544.44%
-15560.78%+13542.55%
-17563.64%+15539.22%
-19566.10%+16537.74%

As the odds rise for underdogs, the potential return climbs, as well. However, that’s offset by the fact that their perceived chances to win shrink.

Should you bet on underdogs?

Don’t just focus on the possibility of a fantastic return if the dog manages to pull off the upset. Anything can happen with sports betting. Even your most confident picks can go awry.

Just remember that underdogs are usually in that position for a reason, and betting on them exclusively carries much greater risk.

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