The minimum win rate needed to break even at given odds, accounting for platform fees.
Break-even probability is the minimum win percentage you need to avoid losing money at a given set of odds or contract price. It accounts for platform fees, which raise the bar above the raw implied probability.
In sports betting, the standard -110 line requires a 52.4% win rate to break even. In prediction markets, fees push the break-even probability above the contract price — a $0.50 contract on Kalshi might need 52-53% to break even after fees.
Understanding your break-even gives you a clear hurdle: if you believe the true probability exceeds the break-even, the bet has positive expected value.
breakEvenProb = effectiveCost / effectivePayout (where effectiveCost and effectivePayout include all fees)
Kalshi Yes at $0.50, taker fee = $0.0175. Effective cost = $0.5175, payout = $1.00. Break-even = 51.75%.
The probability of an outcome implied by the odds. Includes the bookmaker's margin (vig).
Expected Value (EV)The average profit or loss per bet if you made the same wager thousands of times. Positive EV means long-term profit.
VigThe bookmaker's built-in commission. The difference between true odds and what you're offered.