Implied Probability in Sports Betting: Turn Any Line Into a Percentage
The formulas for American, decimal, and fractional odds, how to strip the vig out of a market, and how to tell whether a price is worth betting.
By
Eric Pauly
9 min read
Every Betting Line Is a Probability in Disguise
Implied probability is the win chance a betting price asks you to believe in. When a book hangs -150, it is not just telling you a payout. It is telling you that the bet has to win 60% of the time for you to break even. When it hangs +200, it is saying 33.3%. Once you read odds that way, every line turns into a simple question: is the real chance of this outcome higher or lower than the number the book is charging?
That question sits underneath line shopping, expected value, closing line value, and almost every betting tool on the market. This guide covers the conversion formulas for each odds format, the reverse math for turning your own estimate into a fair price, how to remove the vig from two-way and three-way markets, and the mistakes that make implied probability look more precise than it really is.
article Summary
Implied probability converts betting odds into the win rate a bet needs to break even. For negative American odds divide the odds by the odds plus 100, for positive odds divide 100 by the odds plus 100, and for decimal odds divide 1 by the price. Sportsbook prices include vig, so add both sides of a market, divide each side by that total to get the fair probability, and only bet when your own estimate beats the price you are paying.
How to Calculate Implied Probability From Any Odds Format
The formulas below take a price and return the percentage it implies. The math is simple enough to do on a phone calculator, and our betting odds calculator handles it instantly if you would rather paste a line in and move on.
Negative American Odds (Favorites)
Implied probability = |odds| / (|odds| + 100)
Take the number without the minus sign, then divide it by itself plus 100. At -175, that is 175 / 275, or 63.6%.
Positive American Odds (Underdogs)
Implied probability = 100 / (odds + 100)
At +145, that is 100 / 245, or 40.8%. Plus money always lands under 50%, minus money always lands over 50%, and even money (+100) sits right at 50%.
Decimal Odds
Implied probability = 1 / decimal odds
Decimal odds are the fastest format to convert because the stake is already baked into the number. A price of 1.80 implies 55.6%. A price of 2.40 implies 41.7%. If you ever trade on an exchange that shows decimal prices, this is the only formula you will use.
Fractional Odds
Implied probability = denominator / (numerator + denominator)
At 7/4, that is 4 / 11, or 36.4%. You will mostly see fractional odds on horse racing and UK books, but the logic is the same.
Implied Probability Quick Reference
-300 implies 75.0%
-200 implies 66.7%
-150 implies 60.0%
-120 implies 54.5%
-110 implies 52.4%
+100 implies 50.0%
+120 implies 45.5%
+150 implies 40.0%
+200 implies 33.3%
+300 implies 25.0%
+500 implies 16.7%
One pattern worth noticing in that list: the odds are not linear. Moving from -110 to -120 adds about two percentage points. Moving from +300 to +500 takes away more than eight. Small shifts in favorite pricing matter more than they look, and big shifts in longshot pricing matter less than they look.
Working Backward: Turning Your Probability Into Fair Odds
Converting odds into a percentage tells you what the book thinks. Converting a percentage into odds tells you what the bet is worth to you. This reverse step is where implied probability becomes a decision tool instead of a definition.
Probability to American Odds
Loss probability = 1 minus your win probability
If your win probability is 50% or higher: fair odds = -(win probability / loss probability) × 100
If your win probability is under 50%: fair odds = (loss probability / win probability) × 100
If you think an outcome happens 58% of the time, the fair price is -(0.58 / 0.42) × 100, which works out to about -138. If you think it happens 35% of the time, the fair price is (0.65 / 0.35) × 100, or about +186.
Probability to Decimal Odds
Fair decimal odds = 1 / probability
A 58% estimate gives you 1.72. A 35% estimate gives you 2.86.
Why the Fair Price Is Your Line in the Sand
Your fair price is the worst number you should be willing to accept. Anything better than it is a bet with positive expected value, at least according to your estimate. Anything worse is a bet where you are overpaying. My own process on a prop starts here: I write down the fair price before I look at what the books are offering, because once I see a number on the screen it is far too easy to talk myself into it.
This is also why line shopping matters so much. The same opinion can be a good bet at one book and a bad bet at another, and the only thing that changed was the price.
How to Remove the Vig and Find No-Vig Probability
Raw implied probability includes the sportsbook's cut. If you want to know what the market actually thinks, you have to take the margin out first. That margin goes by a few names (vig, juice, hold, overround), and our guide on how the vig is built into betting odds covers where it comes from. Here is how to remove it.
Step 1: Convert Every Side of the Market
Turn each outcome into its raw implied probability using the formulas above.
Step 2: Add Them Up
The total will land above 100%. The amount over 100% is the overround for that market.
Step 3: Divide Each Side by the Total
No-vig probability = raw implied probability / total implied probability
This is called the multiplicative method, and it is the standard starting point. It spreads the margin across each side in proportion to its price. Our no-vig odds calculator runs this for two-way markets so you can check a line in a few seconds.
Three-Way Markets and Futures
The same steps work for soccer moneylines, where the draw is a third outcome, and for futures boards with dozens of teams. The difference is that the overround tends to grow as you add outcomes. Full futures boards often add up to well past 110%, which is a big reason futures are an expensive place to bet thin opinions.
A Note on Devig Methods
The multiplicative method assumes the book charges the same relative margin on every side. In practice, books often shade longshots more heavily than favorites, so sharper bettors and tools also use other methods (additive, power, and Shin are the common ones) that push more of the margin onto the underdog. For most two-way markets with prices close together, the methods land within a fraction of a percent of each other. The gap widens on lopsided lines and futures.
Using Implied Probability to Judge a Bet
Once you can move between odds and percentages, three practical uses open up.
Break-Even Win Rate
The implied probability of the price you actually bet is your break-even rate. If you bet every side at -110, the bar to stay flat is a 52.4% win rate. If you can get those same bets at -105, the bar drops to 51.2%. Tracking your win rate without tracking the average price you paid tells you very little.
Expected Value
Expected value is the gap between your probability and the price's implied probability, scaled by the payout. If your estimate is higher than the no-vig probability and higher than the implied probability of the price you are getting, the bet has positive expected value. A tool or a model can supply your probability, but the comparison is always the same: your number against the price.
Closing Line Value
The closing line is usually the most accurate price a market produces, because it has absorbed the most information and the most sharp money. Comparing your bet's implied probability to the no-vig probability at close tells you whether you got a good number, regardless of whether the bet won. Our guide to closing line value and how to beat the close goes deeper on tracking it.
The market observation that keeps showing up when I compare prices across books: player props are where the widest gaps between a single book's implied probability and the devigged market tend to appear. Prop markets carry more hold and get less sharp attention, so individual books drift further from consensus before they correct.
Tools and Markets That Show Implied Probability for You
Doing this by hand is worth learning once. Doing it by hand on every line of a full slate is not realistic, which is why +EV tools exist. They pull prices from sharp books and exchanges, remove the vig, and flag lines where a sportsbook is offering better than fair.
EVergreen: Fair Prices You Can Inspect
EVergreen is a $4.99 a month +EV app built for newer bettors. What makes it useful for learning implied probability is that it shows its work. When I tapped into a card during testing, it broke out each book's no-vig price and the share of the fair value that book contributed, and you can adjust those devig weights yourself. It also includes a 21-lesson +EV course. Player props run on about a five minute delay, so it is better suited to pregame betting than chasing fast moves. Code BETSMART14 gets you 14 days free, and our EVergreen review covers the full test.
Bookie Beats: Control Over the Devig
Bookie Beats is built for bettors who want to decide how fair value gets calculated. You choose which sharp books to devig from and set separate EV filters by sport and market, which matters because the right devig for an NFL side is not the right one for a thin player prop. It compares 19 sportsbooks and prediction markets, including Pinnacle, Circa, Novig, ProphetX, and Kalshi. Plans run $100 a month for the pregame tools and $400 a month for Premium with live, new accounts get seven days of full Premium free, and code BETSMART takes $50 off your first month.
Prediction Markets Quote Probability Directly
On a CFTC-regulated exchange like Kalshi, a contract that pays $1 and trades at 62 cents is implying a 62% chance, before trading fees. There is no conversion step, which makes prediction market prices a handy cross-check against sportsbook odds. For a wider look at the category, see our rankings of the best EV betting tools.
Final Thoughts
Implied probability is the translation layer between a betting line and a real decision. Convert the price, strip out the vig, compare it to your own estimate, and the bet either clears the bar or it does not. That process will not win every bet, but it does make sure you know what you are paying for.
Start small: before your next bet, run the line through the odds calculator, check the other side of the market in the no-vig calculator, and write down your own number. A few rounds of that and you will start reading -150 as 60% without thinking about it.
Implied Probability FAQ
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