Evaluate whether a bet is worth taking before you place it.
The odds your sportsbook is offering. Negative for favorites, positive for underdogs.
Your best estimate of the true likelihood this bet wins.
Expected value is the mathematical answer to a simple question: if you placed this exact bet a thousand times at these exact odds, would you come out ahead or behind? It strips away hope, narrative, and gut feeling and replaces them with arithmetic.
A positive EV means the bet earns money over time. A negative EV means it loses money over time. The sportsbook's entire business model depends on offering bets that are negative EV for the bettor. When you find a spot where that relationship flips, where your estimated probability of winning exceeds what the odds imply, you've found a bet worth taking.
That's the concept. The rest is execution: estimating probabilities accurately, finding odds that underprice your side, and repeating the process over a sample large enough for the math to converge.
The formula itself is straightforward. The difficulty is in the inputs, not the math.
Four components:
If the result is positive, the bet has +EV. If negative, the sportsbook has the edge. If zero, it's a breakeven proposition.
The calculator above handles the conversion from American odds to profit automatically. The step-by-step manual calculation, including how to convert odds formats, is covered in the companion tutorial.
The implied probability at -110 is 52.4%. Your 55% estimate gives you a 2.6% edge. On a $100 stake, the EV comes out to roughly +$5.00 per bet. That's a clear +EV situation.
The implied probability at +200 is 33.3%. Your 38% estimate means a 4.7% edge. Even though this bet loses more often than it wins, the payout when it hits more than covers the losses. EV is positive.
The implied probability at -200 is 66.7%. Your 62% estimate is below the implied line. You think the team wins less often than the odds require. This is -EV no matter how likely the team is to win this specific game. The price is wrong for you.
What the calculator output tells you: The verdict (+EV or -EV) answers whether to bet. The edge percentage tells you how much value you're getting. The dollar EV tells you what the average return looks like at your stake size.
The boundary between +EV and -EV comes down to one comparison: is your estimated win probability higher or lower than the implied probability from the odds?
| Odds | Implied Prob | Your Estimate | Edge | EV Status |
|---|---|---|---|---|
| -110 | 52.4% | 55.0% | +2.6% | +EV |
| +150 | 40.0% | 45.0% | +5.0% | +EV |
| -150 | 60.0% | 58.0% | -2.0% | -EV |
| +110 | 47.6% | 47.0% | -0.6% | -EV |
| +300 | 25.0% | 30.0% | +5.0% | +EV |
The +300 row is worth studying. That bet loses 70% of the time. Most bettors would dismiss it as too risky. But the math is clear: a 5% edge is a 5% edge regardless of the win rate. The payout structure compensates for the lower hit rate. This is the gap between how recreational bettors evaluate bets (will it win?) and how serious bettors evaluate them (is the price right?).
Single-bet results are noise. EV is signal. The only way to evaluate whether you're making sound bets is to track your EV over time and see whether your actual results converge toward it.
Feeling strongly about a team is not the same as having a mathematical edge. Edge requires a specific probability estimate that exceeds the implied probability. If you can't state your win probability as a number, you don't have an edge assessment, you have an opinion.
A team that wins 70% of the time is not a good bet if the odds imply they should win 75% of the time. Betting is not about picking winners. It's about finding spots where the probability of winning exceeds what you're being charged to play. The price is everything.
Different books price the same game differently. Getting -105 instead of -110 on a standard bet shifts the implied probability by over a full percentage point. Over hundreds of bets, that difference determines whether you're above or below the EV line.
This is the hardest problem in sports betting. You think you're a 56% bettor, but you're actually at 52%. That 4% gap turns profitable EV assessments into losing ones because every calculation is built on your probability estimate. Track your results, compare estimates to outcomes, and adjust. Honesty with your own numbers is non-negotiable.
Calibration matters: Even professional bettors sustain win rates of 53-57% on standard -110 lines. If your estimated win rates consistently exceed 60%, your estimates likely need recalibrating rather than your bet sizing increasing.
EV answers whether a bet is worth taking. It does not answer how much to wager. Those are two separate questions, and conflating them is a common and expensive mistake.
A bet with a 1% edge and a bet with a 7% edge are both +EV, but they don't deserve the same stake. Larger edges justify larger bets. Smaller edges justify smaller ones. The mathematical framework for sizing bets proportional to your edge is the Kelly Criterion, which takes your EV assessment and translates it into a specific percentage of your bankroll to wager.
The practical workflow is sequential: first use this calculator to confirm a bet is +EV, then use a bet sizing method to determine how much of your bankroll to commit. Skipping the first step means you might be sizing bets on losing propositions. Skipping the second means you might be risking too much on thin edges or too little on strong ones.
Expected value is not a prediction about what will happen on a single bet. It's a statement about what would happen across many bets at the same odds and probability. That distinction is the entire foundation of serious sports betting.
Every bet you place is either +EV or -EV before the game starts. The outcome doesn't change which one it was. A +EV bet that loses was still the right decision. A -EV bet that wins was still the wrong one. If you can internalize that, you're thinking about betting the way professionals do.
Use this calculator before you bet. It takes a few seconds. Over time, those seconds are the difference between being on the right side of the math and the wrong one.
A bet where your estimated win probability exceeds the implied probability from the odds. Over many repetitions, +EV bets produce a net gain. The size of the edge determines how much.
Yes. EV describes the average across many trials, not the outcome of a single bet. A coin flip at +120 odds is clearly +EV, but it still loses roughly half the time. The math converges over hundreds or thousands of bets.
Two approaches: build a statistical model using historical data and situational factors, or compare odds at sharp sportsbooks (Pinnacle, Circa) to derive no-vig fair probabilities. Many bettors use sharp closing lines as a baseline and bet when recreational books offer better odds.
EV measures average profit per bet in dollars. ROI expresses that as a percentage of amount wagered. A $5 EV on a $100 bet equals 5% ROI. They describe the same thing in different units.
Any positive EV is mathematically sound. Professional bettors typically target 2-5% edges. Even 1-2% edges are valuable at volume because they compound over a large sample of bets.