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Free odds & probability calculators

Free odds and probability calculators

Five free, private, in-browser calculators for prediction-market and betting-odds maths: odds converter, implied probability and no-vig calculator, arbitrage stake splitter, Kelly criterion and expected value.

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Last updated: · Written and reviewed by Ken Lin

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Quick answer

Five small calculators for the maths behind prices: convert odds formats, strip the bookmaker margin, check an arbitrage and split stakes, size a position with Kelly, and work out expected value. They run entirely in your browser, accept comma or dot decimals, and every page shows the formula so you can check the result. Educational only — not betting or financial advice.

Odds converterConvert betting odds between decimal, American (moneyline) and fractional formats and see the implied probability instantly. Free, private, works with comma or dot decimals.Implied probability & no-vig calculatorEnter the odds for every outcome of a market (2 to 10 outcomes) to see the implied probabilities, the bookmaker overround and margin, and the no-vig fair probabilities and odds.Arbitrage calculatorCheck whether the best odds across bookmakers or prediction markets form an arbitrage, and split a total stake across 2 or 3 outcomes for an equal return. Free and private.Kelly criterion calculatorCalculate the Kelly fraction from the odds and your probability estimate, with full, half or quarter Kelly and an optional bankroll. Shows the edge and expected value too.Expected value (+EV) calculatorEnter the odds offered and your fair probability (or fair no-vig odds) to see expected value per unit, edge over the break-even probability and expected profit on a stake.

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Pred-Data publishes independent, source-linked explainers about prediction markets and the AI tools used around them. Every factual claim on this page links to a primary or reputable secondary source, checked on the date shown above. We do not run a trading venue, take bets, or give personal advice.

Author: Ken Lin · Corrections: if you spot an error, we review it and date-stamp the fix.

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