Free Tools

Sports Betting Calculators & Tools

Every tool here applies the same mathematics professional bettors use. No registration, no paywall. Run the numbers before you place the bet.

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Kelly Criterion Calculator
f* = (bp − q) / b

Calculate the mathematically optimal stake size for any bet. Enter your edge and the calculator returns the exact fraction of bankroll Kelly theory recommends — with full Kelly, half Kelly, and quarter Kelly options.

American / Decimal / Fractional odds Win probability % Bankroll (optional) Kelly fraction
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Free Tool
Expected Value Calculator
EV = (p × W) − (q × L)

Find out whether a bet has positive or negative expected value before placing it. Enter the odds, your estimated win probability, and your stake — the calculator shows your edge and long-run expectation per 100 bets.

Odds (any format) Estimated win probability Stake amount
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Free Tool
Odds Converter
American ↔ Decimal ↔ Fractional

Convert between American, Decimal, Fractional, and implied probability in one step. Enter both sides of a market to see the vig-free break-even probability — the market's real assessment stripped of the bookmaker's margin.

American odds Decimal odds Fractional odds Implied probability Vig-free probability
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What the tools calculate
Each tool applies a specific mathematical principle
1
Edge first
Every calculation starts with your estimated win probability versus the market's implied probability. No edge, no bet.
2
Size the bet correctly
Kelly tells you what fraction of your bankroll to risk based on the size of your edge. Overbetting is as damaging as betting negative EV.
3
Check the math
Odds conversions let you work across bookmaker formats without arithmetic errors. A conversion mistake is a free source of negative EV.
4
Repeat at scale
These tools are most useful when applied consistently across a large sample of bets. Single-bet results prove nothing; process over 200+ bets does.
Common questions
About these tools
Are these tools free?
Yes. All three tools are fully free and run in your browser. No account is required. Your inputs are not saved or transmitted anywhere.
Do I need to use all three tools for every bet?
Not necessarily, but they address different problems. The EV Calculator tells you whether a bet is worth placing. The Kelly Calculator tells you how much to stake. The Odds Converter removes format confusion when comparing lines across sportsbooks — including vig-free probability when you enter both sides of a market. Together they cover the three core decisions every value bettor faces.
What win probability should I enter?
Your own honest estimate, derived from your model or analysis — not the implied probability in the odds. If you don't have an independent probability estimate, the EV calculation is circular and meaningless. Read the Expected Value guide for worked examples on how to arrive at a calibrated probability.
How is this different from a sports betting app or tipster service?
These tools do not give picks or tell you who to bet on. They give you the mathematics to evaluate a bet you have already identified. The judgment about which games to bet, and what probability to assign, remains yours.
What is Kelly Criterion used for in sports betting?
The Kelly Criterion determines the theoretically optimal fraction of a bankroll to wager on a bet where you have a positive expected value. Staking exactly Kelly maximises long-run bankroll growth. Most practitioners use half-Kelly to reduce variance, accepting slightly lower expected growth in exchange for reduced drawdown risk. The Kelly Calculator lets you run both scenarios.

Learn the concepts behind the tools

The calculators are more useful once you understand what they measure. Start with the guides, or go straight to the complete strategy framework.

Sports betting involves financial risk. No strategy, system, or AI tool guarantees profit. Past results do not predict future performance. Never bet more than you can afford to lose. If betting is causing problems, contact NCPG, BeGambleAware, or Gambling Therapy.

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