Free Expected Value (EV) Calculator

What Is Expected Value in Betting?

Expected value (EV) is the single most important concept in profitable betting. It measures the average amount you expect to win or lose per bet if you placed it an infinite number of times. A bet with positive expected value (+EV) will make you money over time, while a negative expected value (-EV) bet will cost you money.

Every sportsbook and prediction market builds a margin into their odds. This margin means that most bets are -EV for the bettor. Professional bettors make money by finding situations where the true probability of an outcome is higher than what the odds imply -- these are +EV bets.

Think of it like a casino: the house has a small edge on every game, but that edge compounds over thousands of plays into reliable profit. +EV betting puts you on the house side of the equation.

The EV Formula Explained

The expected value formula is straightforward:

EV = (probability of winning x profit if win) - (probability of losing x stake)

This simplifies to:

EV = stake x (true probability x decimal odds - 1)

The edge percentage is the core metric:

Edge% = (true probability x decimal odds) - 1

A positive edge means you have an advantage. For example, if you believe an outcome has a 55% chance of occurring and the decimal odds are 2.00:

• Edge = (0.55 x 2.00) - 1 = 0.10 or 10%
• EV on a $100 bet = $100 x 0.10 = +$10.00
• Break-even win rate = 1 / 2.00 = 50%

Since your estimated probability (55%) exceeds the break-even rate (50%), the bet is +EV. Use the calculator above to run your own numbers with any odds format.

How to Estimate True Probability

The accuracy of your EV calculation depends entirely on your true probability estimate. Here are the methods professional bettors use:

1. No-Vig Odds from Sharp Bookmakers

Sharp bookmakers like Pinnacle (PS3838) have the lowest margins in the industry, typically 2-3%. By removing the vig from their lines, you get a close approximation of the true probability. If Pinnacle prices a market at 1.90/1.95, the no-vig fair odds are approximately 1.976/2.024, implying probabilities of 50.6% and 49.4%.

2. Closing Line Value (CLV)

The closing line -- the odds at the moment the market closes -- is widely considered the most efficient estimate of true probability. Markets aggregate information from thousands of bettors, and by close, most of that information is priced in. Use the CLV tab in the calculator above to check if you are consistently beating the closing line.

3. Statistical Models

Building your own models using historical data, player statistics, and situational factors gives you an independent probability estimate. This is especially valuable in less efficient markets where bookmaker lines may be soft.

What Is Closing Line Value (CLV)?

Closing line value measures whether you got better odds than the market's final price. If you bet a team at 2.10 and the closing line is 1.90, you got better odds than the closing market. The CLV percentage is:

CLV% = (closing implied probability / your implied probability - 1) x 100

In this example: CLV = (52.63% / 47.62% - 1) x 100 = +10.53%. Consistently positive CLV is the strongest evidence that you are a winning bettor, even over small sample sizes where actual results may not yet reflect your edge.

Why +EV Betting Works Long-Term

A single +EV bet can still lose -- variance is real. But over hundreds and thousands of bets, the law of large numbers ensures your results converge toward the expected value. This is why bankroll management matters so much. Use the Kelly Criterion calculator to determine optimal bet sizing based on your edge and bankroll.

Key principles for +EV betting:

• Volume matters. The more +EV bets you place, the faster variance smooths out.
• Track everything. Log your bets, edges, and CLV to verify your process.
• Size correctly. Overbetting destroys bankrolls even with an edge. Kelly or fractional Kelly is standard.
• Diversify. Spread bets across different sports, markets, and venues to reduce correlation.

EV in Prediction Markets

Prediction markets like Kalshi and Polymarket use probability-based pricing (cents for Kalshi, 0-1 for Polymarket). The EV calculation is identical: if you believe a contract's true probability is higher than its market price, buying is +EV.

Prediction markets often offer larger edges than traditional sportsbooks because they attract a broader range of participants, many of whom are trading on opinion rather than data. Cross-market arbitrage -- where the same event is priced differently across venues -- provides guaranteed +EV without needing your own probability estimate. Learn more about value betting vs arbitrage to understand the differences.

Worked Example: Full EV Calculation

Suppose you find a bet on the Lakers to win at American odds of +150 (decimal 2.50). Your model gives the Lakers a 45% chance of winning.

1. Convert to decimal: +150 = (150/100) + 1 = 2.50
2. Break-even win rate: 1 / 2.50 = 40%
3. Edge: (0.45 x 2.50) - 1 = 0.125 or 12.5%
4. EV on $100: $100 x 0.125 = +$12.50
5. Kelly optimal stake: 12.5% / (2.50 - 1) = 8.33% of bankroll

This is a strong +EV opportunity. The implied probability is only 40%, but you estimate 45%, giving you a 12.5% edge. For more on calculating arbitrage opportunities, check our detailed guide.

Frequently Asked Questions

What is expected value in betting?

Expected value (EV) measures the average profit or loss you can expect per bet over the long run. A positive EV (+EV) means the bet is profitable on average, while a negative EV (-EV) means you lose money over time. EV is calculated as: (true probability x profit if win) minus ((1 - true probability) x stake). Professional bettors only place bets with positive expected value.

How do you calculate expected value of a bet?

To calculate EV, use the formula: EV = stake x (true win probability x decimal odds - 1). For example, if you believe an outcome has a 55% true probability and the decimal odds are 2.00 with a $100 stake: EV = $100 x (0.55 x 2.00 - 1) = $100 x 0.10 = $10. This means you expect to profit $10 on average per bet. The edge percentage is (true probability x decimal odds - 1) x 100.

What is a good EV percentage in sports betting?

Any positive EV percentage means a bet is profitable long-term. In practice, sharp bettors often target edges of 1-5%. Edges above 5% are considered excellent but are rare and often close quickly. In prediction markets like Kalshi and Polymarket, edges of 2-8% are more common due to less efficient pricing. Even a 1% edge is valuable when applied consistently with proper bankroll management.

How do you estimate the true probability of an outcome?

There are several methods: (1) Use no-vig (fair) odds from sharp bookmakers like Pinnacle or PS3838, which have the lowest margins. (2) Use closing line odds, since the market at close is the most efficient estimate of true probability. (3) Build your own statistical models using historical data. (4) Average implied probabilities across multiple sharp bookmakers and remove the vig. Most professional bettors combine multiple methods for the best estimate.

Is positive EV betting enough to be profitable?

+EV betting is necessary but not sufficient for long-term profit. You also need proper bankroll management (such as the Kelly Criterion), a large enough sample size to overcome variance, and discipline to avoid tilting after losses. A single +EV bet can still lose; the edge only materializes over hundreds or thousands of bets. Tracking your closing line value (CLV) is the best way to confirm your edge is real.

How does expected value relate to arbitrage betting?

Arbitrage betting guarantees a positive EV on every opportunity by covering all outcomes across different bookmakers. While standard +EV betting relies on your probability estimate being more accurate than the market, arbitrage locks in profit regardless of the result. In prediction markets like Kalshi and Polymarket, arbitrage opportunities arise when prices across platforms sum to less than 100%, creating a guaranteed edge without needing to estimate true probabilities.