Underdog Betting Odds Explained: A Simple Guide for Beginners
If you are new to sports betting, underdog odds can look more confusing than they really are.
You open a sportsbook, see one team at +150 and the other at -175, and suddenly the whole thing feels more complicated than it should. Most beginners quickly learn one basic rule: the team with the plus sign is usually the underdog. That part is true.
But that is only the start.
To really understand underdog betting odds explained, you need to know what those odds mean, how they affect payout, and why an underdog is not automatically a bad bet. In fact, underdogs are often where bettors look for value, because the higher payout can sometimes outweigh the lower win probability.
That is what this guide is about. If you want an example of a traditional sportsbook with broad markets and competitive odds, our 20Bet sportsbook review is a practical place to continue.
What is an underdog in sports betting?
An underdog is the team or player that the sportsbook considers less likely to win.
That does not mean the underdog has no chance. It simply means the market sees that side as the less likely winner compared with the favorite.
In most sportsbooks using American odds:
- the favorite is shown with a minus sign
- the underdog is shown with a plus sign
So if you see:
- Team A -160
- Team B +140
Team B is the underdog.
This is an important point: underdog is a pricing term, not an insult. A team can be an underdog and still be a smart bet. Betting is not about guessing who is stronger in general. It is about deciding whether the odds are fair.
What underdog odds mean on the moneyline
The easiest way to understand underdogs is through the moneyline.
A moneyline bet is simply a bet on which team or player wins the event outright. No point spread, no margin, just the winner.
If an underdog is priced at +150, that means:
- a $100 bet wins $150 in profit
- your total return would be $250, including your original stake
If the underdog is +200, that means:
- a $100 bet wins $200 in profit
- total return would be $300
If the underdog is +300, that means:
- a $100 bet wins $300 in profit
- total return would be $400
The bigger the plus number, the bigger the payout. But it also means the sportsbook sees that outcome as less likely.
That is the basic trade-off with underdogs:
- lower chance of winning
- higher reward when they do win
Why underdog odds are higher
Sportsbooks are balancing risk and reward.
If a team is less likely to win, the sportsbook has to offer a more attractive payout to make bettors interested in taking that side. That is why underdogs come with plus-money odds.
A favorite at -200 might be more likely to win, but a bettor has to risk more money to make a smaller profit.
An underdog at +170 is less likely to win, but the reward is larger if it does.
This is where betting becomes more interesting than simple prediction. The most likely winner is not always the best betting option. Sometimes the favorite is overpriced, and the underdog offers more value.
How underdogs work against the spread
Underdogs do not only appear on the moneyline. They also appear in spread betting.
If a team is listed at +4.5, that means it is the underdog and is getting 4.5 points.
That team covers the spread if it:
- wins the game outright, or
- loses by 4 points or fewer
So if Team B is +4.5:
- Team B wins by any amount = bet wins
- Team B loses by 1, 2, 3, or 4 points = bet wins
- Team B loses by 5 or more = bet loses
This is different from betting the underdog on the moneyline.
A moneyline underdog bet asks the team to win.
A spread underdog bet asks the team to either win or perform better than the market expects.
That difference matters a lot. A team may not be likely enough to win outright, but it may still be a very good spread underdog if the matchup looks close.
How to convert underdog odds into implied probability
This is where underdog odds become much more useful.
Odds do not just tell you the payout. They also tell you the sportsbook’s implied estimate of how likely that outcome is.
For positive American odds, the formula is:
Implied Probability = 100 / (Odds + 100)
Here are a few examples:
- +100 = 50%
- +150 = 40%
- +200 = 33.33%
- +300 = 25%
- +400 = 20%
So if a team is +200, the sportsbook is pricing that team as if it has about a 33.33% chance of winning.
This is one of the most important ideas in betting.
Because the real question is not:
“Can the underdog win?”
The real question is:
“Does the underdog win more often than the odds imply?”
That is the difference between betting for excitement and betting with logic. To judge whether an underdog price is actually fair, it helps to read our implied probability explained guide before looking only at the payout.
Why underdog betting is really about value
A lot of beginners think underdog betting is about trying to predict upsets.
That is only part of the picture.
Smart underdog betting is really about value.
Let’s say a team is priced at +200, which implies a win probability of about 33.33%.
Now imagine you study the matchup and believe the team actually wins closer to 40% of the time.
That means the odds may be undervaluing the underdog. In that case, the underdog could be a smart bet, even though it is still expected to lose more often than it wins.
This is the key mindset shift:
A bet does not need to win most of the time to be good.
It needs to win often enough relative to the price.
That is why underdog betting can be profitable in the right spots. You are not just betting on chaos. You are betting on a number that may be too generous. Because an underdog is only worth backing when the price beats the true chance, our guide to expected value in sports betting takes that logic one step further.
Not all underdogs are the same
This is another mistake beginners make.
They talk about “the underdog” as if all underdogs are the same kind of bet. They are not.
There is a big difference between:
- a slight underdog at +105
- a moderate underdog at +160
- a longshot at +500
All three are underdogs, but the betting logic is different.
A small underdog might be in a game the sportsbook sees as nearly even.
A moderate underdog may be live but clearly considered second-best.
A big longshot is being priced as much less likely to win, which means the payout is larger but the true win rate is much lower.
This matters because your expectations should change with the price.
A +110 underdog can win often enough to become part of a steady betting strategy.
A +600 underdog is usually a very different kind of play and needs a much stronger value case.
How decimal odds show underdogs
If you use a sportsbook that displays decimal odds, underdogs are still easy to identify.
For positive American odds, the decimal conversion is:
(American Odds / 100) + 1
So:
- +150 becomes 2.50
- +200 becomes 3.00
- +300 becomes 4.00
In decimal odds, anything above 2.00 usually indicates the underdog in a two-way market.
Decimal odds also make payout calculation simple:
Stake × Decimal Odds = Total Return
So if you bet $20 at 2.50:
- total return = $50
- profit = $30
Whether you use American or decimal odds, the principle is the same:
higher odds mean bigger payout and lower implied probability.
Common beginner mistakes with underdog betting
A lot of new bettors understand the plus sign but still make bad decisions around underdogs.
Here are the most common mistakes.
Betting underdogs only because the payout looks attractive
A bigger payout is exciting, but excitement is not the same thing as value.
Ignoring implied probability
If you do not know what the odds imply, you cannot judge whether the number is good or bad.
Assuming underdogs are always the “smart” side
Some bettors overcorrect and start thinking all favorites are overpriced. That is not true either.
Treating all underdogs the same
A +110 dog and a +400 dog require completely different expectations.
Not shopping for better odds
Small differences matter. A team at +145 in one book and +160 in another may not look dramatically different, but over time, better prices improve results.
A simple way to think about underdog bets
If you want a practical framework, use this:
First, identify the underdog correctly.
Second, convert the odds into implied probability.
Third, ask whether you believe the team wins more often than that number suggests.
Fourth, compare prices across sportsbooks before betting.
That is a much better process than simply saying:
“I like the dog because the payout is nice.”
Good betting is not about finding teams that can win. Almost every team can win on the right day.
Good betting is about finding teams whose odds are better than their true chances. If you are comparing books for better underdog prices and bonus value, our guide to the best sportsbook rewards is a useful next step.
Should beginners bet underdogs?
Yes, but carefully.
Underdog betting can absolutely make sense for beginners if they understand what they are doing. In some cases, underdogs offer better value than favorites because the market tends to overprice well-known teams or overreact to public opinion.
But beginners should also be realistic.
Underdogs lose more often than favorites. That means even a smart underdog bettor can go through losing stretches. If your only reason for betting the underdog is that the plus-money return looks fun, you will probably make poor decisions.
A better approach is to start with smaller underdogs and close matchups, where the difference between the teams is not extreme and the pricing may be more vulnerable to mistakes.
Final thoughts
If you want underdog betting odds explained in the simplest possible way, here it is:
An underdog is the side the sportsbook believes is less likely to win. On the moneyline, the underdog usually appears with a plus sign, and that number tells you how much profit you would make on a $100 bet. On the spread, the underdog gets points and can often still cash without winning outright. Before choosing a bookmaker only for the headline offer, compare these welcome bonus betting sites alongside the actual prices you are getting on underdogs.
But the real meaning of underdog odds goes deeper than that.
Underdog odds are not just about payout. They are also about implied probability. And once you understand implied probability, you stop thinking like a casual bettor.
You stop asking:
“Can this underdog pull off the upset?”
And you start asking:
“Are these odds better than the underdog’s true chance of winning?”
That is the question that actually matters.
Because in betting, underdogs are not valuable just because they are underdogs.
They are valuable only when the price is right.