Betting odds look like a secret code the first time you see them. A team listed at -150, another at +130, a total of 47.5 with -110 next to it. Once you know what the numbers are doing, though, they are simple. Odds do two jobs at once: they tell you how much you get paid if a pick wins, and they hint at how likely the outcome is in the eyes of the people who set the line.
This guide covers the basics. Each format and concept also has its own deep-dive guide if you want more detail.
What odds actually measure
At heart, odds are a price. If something is very likely to happen, its price is high and the payout is small. If something is unlikely, the price is low and the payout is large.
Think of a coin flip. Heads and tails are equally likely, so a fair price would pay you exactly what you risked: risk 100, win 100. Now imagine a game where one team wins 75% of the time. Nobody would offer even money on that team, because everyone would take it. Instead, you would have to risk more than you can win, something like risking 300 to win 100.
That is the whole idea. Odds balance the payout against the probability.
The three common formats
The same price can be written three different ways depending on where you are in the world.
- American odds (common in the US): -150, +130. A minus number is how much you risk to win 100. A plus number is how much you win on a 100 risk. See American odds explained.
- Decimal odds (common in Europe, Canada and Australia): 1.67, 2.30. Multiply your stake by the number to get your total return. See Decimal odds explained.
- Fractional odds (traditional in the UK and Ireland): 4/6, 13/10. The first number is your profit for every unit of the second number you stake. See Fractional odds explained.
These are just different languages for the same thing. -150, 1.67 and 4/6 are all the same price.
A worked example
Say a game is listed like this:
- Team A: -150
- Team B: +130
If you pick Team A with a 150 stake and they win, you get your 150 back plus 100 profit, for 250 total. With a 30 stake, you would win 20 (30 × 100/150), returning 50.
If you pick Team B with a 100 stake and they win, you get your 100 back plus 130 profit, for 230 total. With a 30 stake, you would win 39 (30 × 130/100), returning 69.
The minus sign marks the favorite (the team expected to win) and the plus sign marks the underdog.
Turning odds into probability
Every price implies a probability, called the implied probability. For American odds:
- Minus odds: risk ÷ (risk + 100). For -150: 150 ÷ 250 = 60%.
- Plus odds: 100 ÷ (odds + 100). For +130: 100 ÷ 230 = 43.5%.
Add those together and you get 103.5%, not 100%. That extra 3.5% is the bookmaker's built-in margin, known as the vig or juice. It is how the house makes money regardless of who wins. Our guide on implied probability and what the vig is go deeper.
Common types of odds you will see
Most game listings show three markets side by side:
- Moneyline: just pick who wins. See moneyline bets.
- Point spread: the favorite has to win by more than a set number of points. See point spreads explained.
- Total (over/under): pick whether the combined score goes over or under a number. See over/under totals.
You will also see futures (like who wins the championship) and parlays (several picks combined into one). Both pay more but are much harder to hit.
Who sets the odds, and why do they change?
Odds are set by oddsmakers who use statistical models, team ratings and information like injuries and weather. After the line opens, it moves as new information arrives and as money comes in on one side. A line that opens at -150 might drift to -170 if a key player on the other team is ruled out.
Odds are not predictions in the strict sense. They are prices designed so the house profits over time. But because markets absorb so much information, they tend to be quite accurate, which is exactly why beating them consistently is hard.
Odds are not guarantees
A team at 75% implied probability still loses one game in four. Underdogs win all the time. Odds describe the long-run likelihood across many similar situations, not what will happen tonight. Treat any single result as one draw from a range of outcomes.
Practice reading odds for free
The fastest way to get comfortable is to look at real lines and make picks without anything at stake. On MockSport you can browse live odds, make free play-money picks with virtual tokens, and see how your reads hold up over time. There is no deposit and no prize, so you can focus purely on learning.
A good beginner exercise: for each game you look at, convert both sides to implied probabilities, then ask yourself whether you think the real chances are higher or lower. Track your answers and you will start to see where your instincts are good and where they are not.
FAQ
What does a minus sign mean in betting odds?
A minus sign marks the favorite. The number shows how much you need to risk to win 100. At -200 you risk 200 to win 100, and the implied probability is about 66.7%.
What does a plus sign mean in betting odds?
A plus sign marks the underdog. The number shows how much you win on a 100 stake. At +250 a 100 stake wins 250, and the implied probability is about 28.6%.
Do the odds tell me who will win?
No. They tell you how likely each side is in the market's view, plus a margin for the house. Favorites lose often, and a single game can go either way.