How to Read Betting Odds

By Cobia Picks · Updated July 3, 2026 · ~7 min read

Odds look like a foreign language until someone shows you the one thing they're actually saying: how likely the market thinks something is, and what you get paid if you're right. Once you can translate any odds format into a probability, you can compare prices across books, spot a bad number, and stop overpaying. This is the plain-English version — American odds, decimal odds, and the conversion that matters most.

American odds: the plus and minus

American odds are built around a $100 reference point, and the sign tells you which side of the matchup you're on.

Favorites (negative numbers)

A minus sign means the team is favored, and the number is how much you must risk to win $100. At -200, you bet $200 to win $100. If it hits, you get back $300 total (your $200 stake plus $100 profit). Scale it however you like: a $20 bet at -200 wins $10; a $50 bet wins $25. The bigger the number, the heavier the favorite and the smaller the payout.

Underdogs (positive numbers)

A plus sign means the team is an underdog, and the number is how much you win on a $100 bet. At +150, a $100 bet wins $150, returning $250 total. A $40 bet at +150 wins $60. The bigger the positive number, the longer the shot and the bigger the payout.

Decimal odds: one number, total return

Decimal odds — standard in Europe and on most exchanges — are simpler in one way: the number is your total return per $1 staked, stake included. Multiply your stake by the decimal to get everything back.

• 2.50 means a $100 bet returns $250 total ($150 profit). That's the same as +150.
• 1.50 means a $100 bet returns $150 total ($50 profit). That's the same as -200.
• 2.00 is a pure coin flip — double your money — the equivalent of +100 or -100 ("even money").

To convert American to decimal: for a favorite, decimal = (100 ÷ number) + 1, so -200 → (100 ÷ 200) + 1 = 1.50. For an underdog, decimal = (number ÷ 100) + 1, so +150 → (150 ÷ 100) + 1 = 2.50. You rarely need to do this by hand, but knowing the relationship keeps you from getting fooled by a format switch.

The real skill: converting odds to implied probability

Here's the part that actually makes you money. Every set of odds contains a hidden probability — the market's estimate of how often that outcome should happen. Convert the odds to that percentage, and you can finally ask the only question that matters: is this priced too high or too low?

The formulas

From decimal odds, implied probability is just 1 ÷ decimal. From American odds:

• Favorite (negative): probability = number ÷ (number + 100). So -200 → 200 ÷ 300 = 66.7%.
• Underdog (positive): probability = 100 ÷ (number + 100). So +150 → 100 ÷ 250 = 40%.
• Even money (+100 / 2.00) → 100 ÷ 200 = 50%.

Worked example: you see a team at +120. That's 100 ÷ 220 = 45.5%. The book is effectively saying "this team wins about 45.5% of the time." If your own research says they win closer to 52%, you've found a mispriced bet. If you think it's more like 40%, the price is a trap. The number stops being decoration and becomes a claim you can agree or disagree with.

Why the book's percentages add up to more than 100%

Add the implied probabilities of both sides of a real game and you'll get a number above 100%. That excess is the vig (also called juice or margin) — the book's built-in commission.

Take a typical -110 / -110 point spread, the most common price in American sports betting. Each -110 side converts to 110 ÷ 210 = 52.4%. Add them: 52.4% + 52.4% = 104.8%. That extra 4.8% doesn't belong to either team — it's the house's cut baked into the price. It's why beating sports betting is hard: you're not just trying to be right, you're trying to be right by more than the vig.

Why Polymarket prices are refreshingly honest

On a prediction market like Polymarket, a share settles at $1 if the outcome happens and $0 if it doesn't, and it trades anywhere from 1¢ to 99¢. That price is the implied probability, directly. A market trading at 63¢ is the crowd saying "about a 63% chance." No plus/minus to decode, no format conversion — the cents are the percent.

Because it's an exchange where buyers and sellers meet, the two sides of a binary market tend to sum close to $1.00 (100%) rather than carrying a fat sportsbook margin. You still pay small fees and cross a spread, but the raw price is far closer to a clean probability. That's a big reason Cobia is built on Polymarket data: when the price already reads as a probability, comparing it to a sharper estimate is straightforward — which is exactly the logic behind +EV betting.