Betting Calculators

Every calculator does one job and shows every step: free, no signup, no black box. Each has a full lesson in the Learn course.

De-vigNo-Vig CalculatorStrip the vig, find the fair price. EdgeExpected Value (+EV) CalculatorPrice your edge before you stake it. SizingKelly Criterion CalculatorSize the stake your edge supports. ArbitrageArbitrage CalculatorSplit stakes when two books disagree. GradingClosing Line Value CalculatorGrade every bet against the close. PromosFree Bet & Bonus Bet CalculatorWhat a bonus token is really worth. CombosParlay CalculatorCombined odds, payout, and compounded vig.FeesKalshi Fee CalculatorYour true break-even after exchange fees. CombosRound Robin CalculatorEvery parlay combination, total risk, payout per hit level. CombosTeaser CalculatorCombined price, and what the bought points must be worth. CombosMiddle CalculatorStake split, loss if it misses, and the required hit rate. ConvertOdds ConverterAmerican, decimal, fractional and cents, every direction. ConvertImplied Probability CalculatorWhat percentage a posted price is actually claiming. ConvertVig & Hold CalculatorThe overround on a market, and what the book keeps. ConvertBreak-Even Win Rate CalculatorHow often a price has to win just to break even. ConvertBet Payout CalculatorStake and odds to profit, return and total back. ManageHedge CalculatorThe stake that equalises profit across both outcomes. Prediction marketsPrediction Market Odds ConverterContract cents to moneyline, decimal and probability. Prediction marketsPrediction Market Arbitrage CalculatorCross-venue gaps, after each side’s fees.

How the calculators chain together

They are a shelf, not a syllabus: pick the one that answers your question. Five of them do happen to chain, though, in the sense that each consumes the previous one’s output.

  1. De-vig turns both sides of a posted market into a fair probability: −110 / −110 implies 104.76% between them, and removing the surplus leaves 50/50. Nothing downstream works without it, because a posted price is not a probability. Guide: How to De-Vig Odds.
  2. Expected value takes that fair probability and a softer price and returns EV = p·b − (1−p) per dollar. If the two agree, the answer is $0, printed as $0 and not rounded into something that looks actionable. Guide: Expected Value (+EV) Betting.
  3. Kelly takes the same probability and price and returns a stake fraction. Half Kelly is the default, because edge estimates are noisy and overbetting punishes harder than underbetting. Guide: The Kelly Criterion.
  4. Arbitrage is the discontinuous cousin: two venues disagree enough that both sides can be covered. It needs no probability estimate at all, only the two prices. Guide: Arbitrage Betting.
  5. Closing line value closes the loop, comparing the price you recorded against the de-vigged close, the fastest honest read on whether the expected value was real. Guide: Closing Line Value.

The rest stand alone: the free bet calculator prices a promotional token, the parlay calculator shows what the margin does when it compounds (Betting Mistakes), and the Kalshi fee calculator converts an exchange price into the probability a position actually needs (Books vs. Exchanges).

Starting cold? Start at no-vig: almost every wrong answer in betting math traces back to treating a posted price as a probability. The beginner lesson assumes nothing.

Why every step is shown

These pages print the derivation, not just the answer: the de-vig method, the intermediate probabilities, the timestamps. If a number can’t be derived on screen, it doesn’t ship. They print $0 when there is no edge rather than rounding up, and they issue no picks.

The math is open source in the MIT-licensed teachersbettextbook package, so any number here reproduces in four lines of Python. See open source, methodology and the formula sheet.