How to Read Betting Odds
Odds look like gibberish at first. Plus signs, minus signs, weird decimals. But once they click, you can look at any price and know right away what the book thinks will happen and what it pays.
Three ways to write the same thing
Odds come in three flavors. They all tell you the same two things, how likely something is and what it pays, just dressed up differently.
American odds
The US standard, built around $100. A minus number is the favorite, and it tells you what you have to risk to win $100. So -150 means you put up $150 to win $100. A plus number is the underdog, and it tells you what $100 wins. So +150 means a $100 bet wins you $150. The bigger the number, the further the game is from a coin flip.
Decimal odds
You'll see these everywhere outside the US, and they're the easiest for doing math. The number is your total return per $1 you bet, your stake included. So 2.50 means a $100 bet comes back as $250 ($150 profit plus your $100). Under 2.00 is a favorite. Over 2.00 is a dog.
Fractional odds
The old-school British style. 5/1 ("five to one") pays 5 profit for every 1 you risk. 1/2 pays 1 for every 2 you put up, so that's a favorite.
An even-money dog can be written +100, or 2.00, or 1/1. A clear favorite might be -200, or 1.50, or 1/2. Whichever format you're staring at, the job is the same: know at a glance whether you're looking at a favorite or an underdog.
Turn any price into a percentage
Here's the move that actually matters. Turn a price into its implied probability, which is just the win rate the odds are assuming:
- Minus American: the number divided by (the number plus 100). So -150 becomes 150 / 250, or 60%.
- Plus American: 100 divided by (the number plus 100). So +150 becomes 100 / 250, or 40%.
- Decimal: just 1 divided by the decimal. So 2.50 becomes 1 / 2.5, or 40%.
Once a price is a percentage, you can hold it up against your own read on the game. That comparison is the whole ballgame when it comes to finding value.
Why the two sides add up to more than 100
Add both sides of a game and you'll land a little over 100%. That extra bit is the book's cut, the vig. It's why reading odds and removing the vig go together. One shows you what the book is charging. The other shows you the fair price hiding underneath.
Key takeaways
- American odds run off $100: minus is the favorite (risk that to win 100), plus is the dog (what 100 wins).
- Decimal odds show your total return per $1. Fractional odds show profit per unit you risk.
- Turn any price into an implied probability so you can compare it to your own read.
- The two sides always total more than 100%. That gap is the book's vig.