Decimal odds tell you the total you get back for every $1 you bet, stake included. Fractional odds tell you the profit compared to your stake. So 3.50 and 5/2 are the same price, and both equal +250 in American odds.
US sportsbooks show American odds by default. But once you read odds from outside the US, from racing, or from a settings menu with a format switch, you'll run into the other two formats. This guide covers how each one works, the exact formulas to convert between all three, a reference table of common prices, and why decimal is the easiest format for parlay math.
- Decimal odds = total return per $1 staked. A $10 bet at 2.50 returns $25 ($15 profit).
- Fractional odds = profit ÷ stake. 5/2 means you win $5 for every $2 you risk.
- Decimal = fractional + 1. So 5/2 = 2.5 + 1 = 3.50.
- Implied probability = 1 ÷ decimal odds. The fastest conversion there is.
- To price a parlay, multiply the decimal odds of each leg.
How decimal odds work
A decimal price is a multiplier. Multiply your stake by it and you get your total return if the bet wins: your profit plus your stake back.
Profit = Stake × (Decimal odds − 1)
You bet $20 at 2.40. Total return: $20 × 2.40 = $48. Profit: $48 − $20 = $28.
You bet $20 at 1.65. Total return: $20 × 1.65 = $33. Profit: $13.
Anything above 2.00 pays more than even money. Anything below 2.00 is a favorite.
2.00 is the dividing line. It's even money, the same as +100. A decimal price can never be below 1.00, because 1.00 would just give you your stake back. That's how books handle a cancelled leg in a parlay: at least one book's published rules say a cancelled selection gets set to 1.00 and the parlay's odds are recalculated.
How fractional odds work
Fractional odds are profit over stake. The number on the left is what you win. The number on the right is what you risk to win it.
Total return = Profit + Stake
At 5/2 (said "five to two"), you win $5 for every $2 you risk.
A $10 bet: profit = $10 × (5 ÷ 2) = $25. Total return = $25 + $10 = $35.
Same bet at 3.50 decimal: $10 × 3.50 = $35. Identical.
When the left number is bigger, like 5/2 or 3/1, you're looking at an underdog. When the right number is bigger, like 1/2 or 4/6, it's a favorite. "Evens" is 1/1, so $10 wins $10.
You bet $30 at 4/6. Profit = $30 × (4 ÷ 6) = $20. Total return = $50.
In decimal that's 1.67 (rounded). In American, it's -150.
Converting between decimal, fractional and American
You only need a handful of formulas. American odds have two cases (plus and minus), so those conversions do too.
Fractional ↔ decimal
Fractional = (Decimal − 1), written as a fraction
Example: 2.75 − 1 = 1.75 = 7/4. And 7/4 = 1.75, plus 1 = 2.75.
American → decimal
Minus odds: Decimal = 1 + (100 ÷ |American|)
Example: +250 → 1 + 2.50 = 3.50. And -110 → 1 + (100 ÷ 110) = 1.909.
Decimal → American
Decimal below 2.00: American = −100 ÷ (Decimal − 1)
Example: 2.40 → +(1.40 × 100) = +140. And 1.65 → −100 ÷ 0.65 = −153.8, which rounds to -154.
Any format → implied probability
Example: 1 ÷ 2.40 = 41.7%. 1 ÷ 1.65 = 60.6%. That's the same number you'd get from the American formulas in our implied probability guide, but with one step instead of two cases. Remember that these are vig-inflated numbers. Add both sides of a market and you'll get more than 100%. That gap is the vig.
Common prices in all three formats
Every row below comes from the formulas above. Decimals are rounded to two places and probabilities to one.
| American | Decimal | Fractional | Implied probability |
|---|---|---|---|
| -300 | 1.33 | 1/3 | 75.0% |
| -200 | 1.50 | 1/2 | 66.7% |
| -150 | 1.67 | 4/6 (2/3) | 60.0% |
| -120 | 1.83 | 5/6 | 54.5% |
| -110 | 1.91 | 10/11 | 52.4% |
| +100 | 2.00 | 1/1 (evens) | 50.0% |
| +120 | 2.20 | 6/5 | 45.5% |
| +150 | 2.50 | 3/2 | 40.0% |
| +200 | 3.00 | 2/1 | 33.3% |
| +250 | 3.50 | 5/2 | 28.6% |
| +300 | 4.00 | 3/1 | 25.0% |
| +500 | 6.00 | 5/1 | 16.7% |
Notice -110. The exact decimal is 1.909, and the fraction is 10/11, so you risk $11 to win $10. Two-decimal displays round that to 1.91, and 1.91 converts back to about -109.9. Rounding is small on one bet, but it's why converted prices sometimes look off by a point.
Comparing prices across books
Decimal also makes line shopping easy to see. Say one book has your side at 1.91 and another has it at 1.95. On a $100 bet, that's $91 profit versus $95, so the better price pays $4 more for the exact same outcome. In probability terms, you need to win 1 ÷ 1.91 = 52.4% of the time at the first price, but only 1 ÷ 1.95 = 51.3% at the second. Higher decimal, lower bar to clear. Over hundreds of bets, small gaps like that add up.
Why decimal odds make parlay math easy
In American odds, pricing a parlay is a chore. In decimal, you just multiply.
Parlay return = Stake × Parlay decimal
Leg 1 is -110 (1.909). Leg 2 is +150 (2.50). Combined: 1.909 × 2.50 = 4.773.
A $10 parlay returns $10 × 4.773 = $47.73, or $37.73 profit. In American, that's about +377.
Two multiplications. No sign juggling.
Decimal also shows you what parlays cost. Three legs at -110: 1.909 × 1.909 × 1.909 = 6.958, an implied probability of 1 ÷ 6.958 = 14.4%. If each leg is really a coin flip, the true chance of hitting all three is 0.5 × 0.5 × 0.5 = 12.5%, which would be fair at 8.00. The gap between 6.958 and 8.00 is the vig stacking up on every leg. We break it down further in the real cost of parlays.
Which format should you use?
Whichever one you can do math in fastest. The price is the same in every format. Only the label changes.
- Decimal is best for parlays, implied probability and comparing books quickly. Higher number = bigger payout. That's it.
- Fractional is best when you think in "risk this to win that." It's common in racing and in odds quoted outside the US.
- American is what US books show by default, and it's what our +EV Calculator takes as input.
Whatever format you use, the job doesn't change. Turn the price into a probability, compare it to your own estimate, and only bet when you have an edge. That's rule three of the System. If a term here is new to you, look it up in the glossary.
The bottom line: Decimal is total return per $1. Fractional is profit over stake. Decimal = fractional + 1, and implied probability = 1 ÷ decimal. Learn those two lines and you can read any odds board in the world.
Frequently asked questions
How do you read decimal odds?
Multiply your stake by the decimal number to get your total return, including your stake. A $10 bet at 2.50 returns $25, which is $15 profit. Anything above 2.00 pays better than even money, and anything below 2.00 is a favorite.
What does 5/2 mean in betting?
5/2 means you win $5 in profit for every $2 you risk. A $10 bet wins $25 and returns $35 total. In decimal odds that's 3.50, and in American odds it's +250.
How do I convert decimal odds to American odds?
If the decimal is 2.00 or higher, subtract 1 and multiply by 100, then add a plus sign: 2.40 becomes +140. If it's below 2.00, divide -100 by the decimal minus 1: 1.65 becomes about -154.
How do I get implied probability from decimal odds?
Divide 1 by the decimal odds. 1 divided by 2.50 is 40 percent, and 1 divided by 1.91 is about 52.4 percent. Those numbers include the vig, so both sides of a market add up to more than 100 percent.
Are decimal odds better than American odds?
No. The price is the same in every format, so neither one pays more. Decimal is just easier for parlay math and implied probability, while American is what US sportsbooks show by default.
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