If you bet in the US, you see American odds everywhere: -110, +150, -200. They're compact, but they don't tell you much at a glance until you know how to read them. This post covers what the numbers mean, how to convert them into other formats, and how to turn any price into the probability it implies.
Reading plus and minus
American odds are built around a $100 bet.
A plus sign shows how much you win on a $100 stake. +150 means a $100 bet profits $150. You get $250 back in total: your $100 plus $150.
A minus sign shows how much you need to stake to win $100. -110 means you risk $110 to profit $100. On a $100 bet, you'd profit $100 × (100 ÷ 110) = $90.91.
+100 is even money. Risk $100, win $100.
A plus price is the underdog side: it pays more than you risk. A minus price is the favorite: you risk more than you win. On a two-way prop, both sides are often negative (like -110 / -110) because the book's margin sits on top of a near coin flip.
Converting to decimal odds
Decimal odds show the total return per $1 staked, including the stake. They're the format used in most of the world, and they're the easiest one to do math with.
- Positive odds: decimal = 1 + (odds ÷ 100). So +150 is 1 + 1.50 = 2.50.
- Negative odds: decimal = 1 + (100 ÷ |odds|). So -110 is 1 + 0.909 = 1.909.
Going back the other way:
- Decimal of 2.00 or more: American = (decimal − 1) × 100, with a plus sign. So 2.40 is +140.
- Decimal under 2.00: American = −100 ÷ (decimal − 1). So 1.80 is -125, and 1.25 is -400.
Decimal odds are what you multiply when you work out a parlay. See how to calculate parlay odds.
Converting to fractional odds
Fractional odds, common in the UK and Ireland, show profit relative to stake. 3/2 means you win $3 for every $2 you risk.
- Positive odds: fraction = odds / 100, simplified. +150 is 150/100, which is 3/2. +250 is 5/2.
- Negative odds: fraction = 100 / |odds|, simplified. -200 is 100/200, which is 1/2. -110 is 100/110, which is 10/11.
+100 is 1/1, usually called "evens".
Converting to implied probability
This is the conversion that matters most. Implied probability is the win rate a price needs to break even. If you think a bet wins more often than its implied probability, the price is in your favor.
- Positive odds: 100 ÷ (odds + 100). So +150 is 100 ÷ 250 = 40%.
- Negative odds: |odds| ÷ (|odds| + 100). So -110 is 110 ÷ 210 = 52.38%.
- From decimal: 1 ÷ decimal. So 2.50 is 40%.
That's why -110 is not a 50/50 price. A bet at -110 has to win 52.38% of the time just to break even. The extra 2.38 points is how the book makes money.
A reference table
| American | Decimal | Fractional | Implied probability |
|---|---|---|---|
| -200 | 1.50 | 1/2 | 66.67% |
| -150 | 1.67 | 2/3 | 60.00% |
| -110 | 1.91 | 10/11 | 52.38% |
| +100 | 2.00 | 1/1 | 50.00% |
| +150 | 2.50 | 3/2 | 40.00% |
| +250 | 3.50 | 5/2 | 28.57% |
A few patterns worth noticing:
- -200 and +200 are not mirror images. -200 implies 66.67%. +200 implies 33.33%. They add up to 100% only because there's no margin in this comparison. On a real two-way market, the two sides add up to more.
- Small changes near even money matter more than they look. Going from -110 to -120 raises the break-even rate from 52.38% to 54.55%. That's more than two points for a ten-cent move.
- Long odds compress. The gap between +250 (28.57%) and +300 (25.00%) is about 3.6 points. The gap between +1000 (9.09%) and +1100 (8.33%) is under a point.
Two-way prices include the margin
On a player prop listed at over -115, under -105, the implied probabilities are 53.49% and 51.22%. They add up to 104.71%. The extra 4.71% is the book's margin.
To find the book's actual estimate of each side, you divide each one by the total. That's called removing the vig, and it's covered step by step in no-vig odds. It's the starting point for working out whether a price at another book is good.
Common mistakes
- Treating -110 as a coin flip. It's a 52.38% break-even, not 50%.
- Comparing favorites by the size of the number alone. -150 to -130 and -300 to -280 are both 20-cent moves, but the first is worth 3.5 points of implied probability and the second only about 1.3.
- Forgetting the stake in decimal odds. A decimal price of 2.50 returns $2.50 per $1, which is $1.50 profit, not $2.50.
The practical takeaway
The quickest way to judge any American price is to turn it into implied probability. A minus number needs to win more than half the time. A plus number can win less often and still be a good bet. And the same prop at two different prices is two different bets.
The odds converter switches between American, decimal, fractional and implied probability instantly, which is handy when you're comparing prices across books that display them differently.