How to Convert Betting Odds (American, Decimal, Fractional)
American, decimal, and fractional odds are three notations for the same price. Convert American odds to decimal by dividing by 100 and adding 1 (positive) or dividing 100 by the absolute value and adding 1 (negative); subtract 1 from decimal for the fractional ratio. Reformatting never changes the implied probability or the bookmaker’s margin.
This guide is part of the Sharper Points sports betting learning path.
How to Convert Betting Odds (American, Decimal, Fractional)
Sportsbooks don’t all speak the same language. US books quote American odds like -110 or +240. European exchanges and most parlay tools default to decimal odds like 1.91 or 3.40. UK and Irish books still post fractional odds like 10/11 or 5/2. Same price, three different-looking numbers — and here’s the secret: every one of them is just a probability in disguise.
If you only read the plus and minus signs, you’re playing the sportsbook’s game. If you convert every price into one common format, you’re playing math — and math is the only way to compare a line across books and formats and know you’re actually getting the better number.
This guide covers the formula for every conversion — American ↔ decimal, decimal ↔ fractional, and American → implied probability — with worked examples for each. For the instant version, run any of these through the Odds Converter, which handles all three formats and shows implied probability in one place.
Converting American Odds to Decimal and Fractional
American odds show a dollar profit ($100 stake for positive odds, or the stake needed to win $100 for negative odds). Converting to decimal folds the stake back into the payout; converting to fractional expresses the same payout as a ratio.
American → Decimal
The Formula:
Positive odds: Decimal = (Odds / 100) + 1
Negative odds: Decimal = (100 / |Odds|) + 1
Example: Converting +120 and -150
+120 → (120 / 100) + 1 = 2.20 decimal.
-150 → (100 / 150) + 1 = 1.6667 decimal.
Decimal odds are the full payout multiplier on your stake, including the stake itself — a $100 bet at 2.20 decimal returns $220 total ($120 profit) if it wins.
Decimal → Fractional
The Formula:
Fractional ≈ Decimal − 1, expressed as a simplified ratio.
Example: Converting 1.909 and 1.6667
1.909 decimal → 1.909 − 1 = 0.909 ≈ 10/11 fractional (the classic -110 price).
1.6667 decimal → 1.6667 − 1 = 0.6667 ≈ 2/3 fractional (the -150 price above).
Fractional odds tell you the profit-to-stake ratio directly: 10/11 means an $11 stake profits $10 if it wins — the same bet as -110 American or 1.909 decimal.
None of these conversions changes the bet itself. Reformatting -110 as 1.909 decimal or 10/11 fractional doesn’t change your payout, your break-even probability, or the sportsbook’s margin — it only changes which numbers you’re looking at. Use whichever format the book you’re comparing against actually displays, and convert to compare apples to apples.
Converting American Odds to Implied Probability
Converting to a payout format (decimal or fractional) tells you what you’d win. Converting to implied probability tells you what the sportsbook thinks your odds of winning actually are — the number you need for EV and no-vig math.
The formula changes slightly depending on whether the odds are positive (+) or negative (-). Don’t worry; you don’t need a calculus degree. Just a calculator.
Converting Positive Odds (+)
Positive odds (e.g., +120, +200) show how much profit you make on a $100 bet. They usually indicate the underdog or a less likely outcome (less than 50%).
The Formula:
Implied Probability = 100 / (Odds + 100)
Example: Converting +120
Let's say you're looking at an underdog priced at +120.
- Add the odds to 100:
120 + 100 = 220 - Divide 100 by that result:
100 / 220 = 0.4545 - Convert to percentage:
45.45%
The Insight: When a book gives you +120, they are saying, "We think this happens roughly 45% of the time." If your model says it happens 50% of the time, you have an edge.
Converting Negative Odds (-)
Negative odds (e.g., -150, -240) show how much you must bet to win $100. These are usually the favorites.
The Formula:
Implied Probability = Absolute Odds / (Absolute Odds + 100)
(Note: "Absolute" just means ignoring the minus sign. Treat -150 as 150.)
Example: Converting -150
You want to bet on a favorite priced at -150.
- Add the absolute odds to 100:
150 + 100 = 250 - Divide the absolute odds by that result:
150 / 250 = 0.60 - Convert to percentage:
60.00%
The Insight: At -150, the market implies a 60% win rate. If you think the team only has a 55% chance to win, this is a bad bet—even if they are the "better" team.
Quick note: implied probability usually includes the sportsbook's vig, so it's not a "true" probability. To estimate a market-fair probability, remove the vig.
Understanding Break-Even Percentage
Implied probability is the break-even win rate for that price.
If you bet on -110 odds exclusively, you need to win 52.38% of your bets just to end up with $0.00 profit. That is your hurdle rate.
- If your win rate is higher than the break-even percentage, you are profitable.
- If your win rate is lower, you are donating to the sportsbook’s light bill.
Many bettors think 51% makes them sharp. At -110, it’s still negative ROI — you’re risking $110 to win $100, which is why you need 52.38% to break even. Knowing the break-even percentage keeps you honest. It forces you to ask: "Do I really win this bet often enough to justify the price?"
Quick Reference Table: The Cheat Sheet
Don’t want to run the math every time the line moves? Keep this table handy. It covers the most common lines you’ll see in the NFL, NBA, and MLB.
Break-even win rate for each price (before no-vig conversion or line shopping).
| American Odds | Break-Even Win Rate |
|---|---|
| -200 | 66.67% |
| -175 | 63.64% |
| -150 | 60.00% |
| -120 | 54.55% |
| -110 | 52.38% |
| +100 (Even) | 50.00% |
| +110 | 47.62% |
| +130 | 43.48% |
| +150 | 40.00% |
| +200 | 33.33% |
Note: As the payouts get higher (positive odds), the required win rate drops. As the price gets steeper (negative odds), you need to be right much more often.
Line shopping matters: moving from -110 to -105 lowers your break-even rate and increases long-run ROI. For fractional-to-decimal lookups on common UK-style prices (10/11, 11/4, 11/8, 4/5, 6/4, and dozens more), the Odds Converter's reference table has every conversion precomputed.
Stop Guessing, Start Calculating
If your "gut feeling" isn’t backed by data, it’s just heartburn. Sports betting isn't about picking winners; it's about buying probability at a discount.
Now that you can convert between American, decimal, and fractional odds, and read the implied probability behind any of them, you can spot when a sportsbook’s price is off. But doing this manually for every game on the slate is slow, and speed is currency in this market.
Ready to automate your edge?
Don't waste time punching numbers into a calculator. Run any price through the Odds Converter to move between formats instantly, then use our EV Calculator to identify +EV opportunities where your probability estimate beats the price. Head over to the Betting Lines page to make sure you're always grabbing the best price available.
The book builds the stadium. We just mark where the blueprint is wrong.
Odds Conversion FAQ
What is implied probability?
Implied probability translates betting odds into a percentage chance of an event happening, according to the bookmaker’s price.
What is break-even percentage?
Break-even percentage is the win rate you need to hit zero profit at a given set of odds. If your win rate is higher, you’re profitable. Lower, you're giving money to the house.
How do I convert decimal odds to American odds?
If decimal odds are 2.00 or higher, American odds equal (decimal − 1) × 100, shown as a positive number. If decimal odds are below 2.00, American odds equal −100 / (decimal − 1). For example, 1.909 decimal converts to −100 / 0.909 ≈ −110 American.
How do I convert fractional odds to decimal?
Divide the numerator by the denominator and add 1: 10/11 becomes 10 / 11 + 1 = 1.909 decimal. 11/4 becomes 11 / 4 + 1 = 3.75 decimal.
Why do both sides add to more than 100%?
Because the sportsbook bakes in the vig (their cut), so the total implied probability typically exceeds 100%. The overage is their edge.
What’s the fastest way to convert odds to probability?
Use these shortcuts:
+ odds → 100 / (odds + 100) and - odds → abs(odds) / (abs(odds) + 100). Or, use our Odds Converter to get the probability instantly alongside the American, decimal, and fractional values — the dedicated Implied Probability Calculator is the same math without the format conversion, useful when probability is the only thing you need.
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