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EV and Edge Calculator
Compare a fair probability against market odds to compute edge, , , and expected value per dollar wagered. The first filter on every bet: if is not positive, do not place it.
EV and Edge Calculator
Compare a fair probability against market odds to estimate edge, fair price, and expected value.
Expected value: the only number that matters
EV = (true_prob × win_payout) − ((1 − true_prob) × stake). The win_payout uses decimal odds minus 1 — at -110 the win_payout per $100 stake is $90.91. A 55% true probability at -110 yields EV = 0.55 × 90.91 − 0.45 × 100 = +$5.00 per $100, or a 5% return. Notice that hit rate alone does not capture this: 70% at -300 yields EV = 0.70 × 33.33 − 0.30 × 100 = −$6.67. Pros optimize for EV, not win rate.
Edge: the gap between your probability and the market's
Edge in percentage-point form is edge = (true_prob − implied_prob) × 100. A -110
line implies 52.38%; a true probability of 55% gives 55.00 − 52.38 = 2.62 percentage points of
edge. The offered price's is the break-even threshold for EV at
that price, including the bookmaker's . Removing vig
from both sides of the market gives a no-vig fair chance: an estimate of the market's view.
Use that as a comparison for your probability estimate, but keep the offered-price break-even
threshold when judging EV at -110.
Worked example: 55% true probability at -110
Implied probability of -110 = 52.38%. Probability gap = 55.00 − 52.38 = 2.62 percentage points. Fair price at 0.55 implied = decimal 1 / 0.55 = 1.818, American ≈ -122. The market is offering -110 when fair price is -122 — a 2.62 percentage-point model-market difference. EV per $100 stake = 0.55 × $90.91 − 0.45 × $100 = +$5.00. Full Kelly stakes (0.55 × 0.9091 − 0.45) / 0.9091 = 5.5% of bankroll; at quarter Kelly with a $10,000 bankroll that is 1.375%, or $137.50.
FAQ
What is expected value (EV) in sports betting?
EV is the average dollar return per wager if you placed the same bet at the same price thousands of times. The formula is EV = (true_prob × win_payout) − ((1 − true_prob) × stake). Positive EV means the formula returns an average above zero; negative EV means it returns an average below zero. Win rate alone does not include price — a 70% hit rate at -300 and a 53% hit rate at -110 produce different calculated values.
How is edge calculated and what counts as a "good" edge?
Edge is the gap between your true probability and the market's implied probability, expressed in percentage points: edge = (true_prob − implied_prob) × 100. The calculator reports that difference without judging its quality. A large gap can reflect a stale line, an error, or a misestimated probability, and small gaps can be within the probability estimate’s uncertainty.
Why does the calculator show a "fair price"?
The fair price is the American odds equivalent of your true probability. If your model says a bet is 55% to win, the fair price is roughly -122 (decimal 1.82). If the book is offering -110 (decimal 1.91), the offered odds differ from the calculated fair price. This comparison describes the difference between the entered probability and the offered odds; it does not predict the result.
How should I interpret the calculated probability gap?
The result is the entered probability minus the offered-price break-even probability. The no-vig fair chance estimates the market view, while the offered price sets the EV break-even threshold. Treat the result as an input-dependent estimate because probability estimates have error bars.
How is this different from the Kelly calculator?
The EV calculator estimates an average return from the entered probability, odds and stake. The Kelly calculator uses the same probability and odds with a bankroll to calculate a stake fraction. Both outputs depend on the inputs and do not predict an outcome.
Recover the book's true probability before computing edge or EV.
Use the same inputs to calculate a stake fraction.
Verify the bet beat the close — the leading indicator of long-run EV.