Prop Bet Calculator
Calculate implied probabilities and expected value for over/under and prop bets. Enter values for instant results with step-by-step formulas.
Reviewed by Sher, Sports Science & Nutrition Specialist
Formula
EV = (Prob x Profit) - ((1 - Prob) x Stake)
For each side of a prop bet, calculate the implied probability (1/odds), remove the overround to find true probabilities, then compare against your estimated probability. Expected value is your estimated probability times the profit minus the loss probability times the stake. Positive EV indicates a value bet.
Worked Examples
Example 1: Player Passing Yards Prop Analysis
Problem:A QB passing yards over/under is set at 275.5. Over odds: 1.87, Under odds: 1.95. You estimate 58% chance of going over. $100 stake. Is the over a value bet?
Solution:Implied over = 1/1.87 = 53.5%\nImplied under = 1/1.95 = 51.3%\nTotal = 104.8%, Overround = 4.8%\nTrue prob over = 53.5/104.8 = 51.0%\nYour estimate: 58% (7% edge over true implied)\nEV over = (0.58 x $87) - (0.42 x $100) = $50.46 - $42.00 = $8.46\nEV% = 8.46%\nKelly = (0.58 x 0.87 - 0.42) / 0.87 = 9.7%
Result:Over is +EV: +$8.46/bet (8.46%) | Edge: 7% | Kelly: 9.7%
Example 2: Game Total Over/Under Analysis
Problem:Game total is set at 220.5. Over 1.91, Under 1.91. You estimate 47% over probability. Should you bet the under?
Solution:Implied each side = 1/1.91 = 52.4%\nTotal = 104.8%, Overround = 4.8%\nTrue prob each = 50%\nYour estimate under = 53%\nEV under = (0.53 x $91) - (0.47 x $100) = $48.23 - $47.00 = $1.23\nEV% = 1.23%\nSmall edge, borderline value\nKelly = (0.53 x 0.91 - 0.47) / 0.91 = 1.3%
Result:Under is marginally +EV: +$1.23/bet (1.23%) | Kelly: 1.3% (small bet)
Frequently Asked Questions
What is a prop bet and how does it differ from traditional bets?
A proposition bet, or prop bet, is a wager on a specific occurrence or non-occurrence within an event rather than on the final outcome itself. While traditional bets focus on who wins or loses, prop bets can cover anything from individual player statistics like passing yards or points scored, to game events like the first team to score, or even non-athletic events during major games. Props can be player props, team props, or game props. They are especially popular during major events like the Super Bowl where hundreds of prop markets are available. Props give bettors opportunities to exploit specialized knowledge about specific players or situations.
How are over/under lines set for prop bets?
Sportsbooks set over/under lines using a combination of historical data, statistical models, and market demand. For a player passing yards prop, the book analyzes the quarterback average performance, the opposing defense ranking against the pass, weather conditions, game pace projections, and other contextual factors. The line is initially set by odds compilers and then adjusted based on where the betting action flows. If heavy money comes in on the over, the book will move the line up to balance their liability. Sharp bettors who bet early often move the lines significantly. Understanding how lines are set helps identify potential value when your analysis disagrees with the market.
What does implied probability tell me about a prop bet?
Implied probability converts the decimal odds into a percentage that represents how likely the sportsbook believes the outcome is, including their built-in margin. For a prop with over odds of 1.91 and under odds of 1.91, each side has an implied probability of 52.4 percent, totaling 104.8 percent. The extra 4.8 percent is the bookmaker overround. By removing the margin, you find the true implied probabilities are roughly 50/50. If your own analysis suggests the over probability is actually 58 percent, you have found significant value. Always compare your estimated probability against the implied probability after removing the margin to identify genuine betting opportunities.
How do I find value in player prop bets?
Finding value in player props requires developing a systematic approach. Start by building a database of player performance metrics and identifying trends related to opponent matchups, home versus away splits, rest days, and weather conditions. Compare your projected stat lines against the posted lines to find discrepancies. Look for situational edges like a receiver facing a weak secondary, or a running back facing a team that allows high rushing yards. Track line movement across multiple sportsbooks to identify where the market may be mispricing a prop. Using a projection model that accounts for pace of play and game script is particularly effective for identifying over/under value.
References
Reviewed by Sher, Sports Science & Nutrition Specialist · Editorial policy