Free calculator library

Betting and prediction-market calculators

Check probability, fair price, expected value, payout, and position-sizing math with clear inputs and live results.

Outputs are informational estimates based on your inputs, not predictions or guarantees.

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Core calculators

Market pricing

No-Vig

Remove market margin to estimate fair probabilities, prices, and hold.

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Multi-leg payout

Parlay

Combine multiple prices to estimate total odds, payout, profit, and implied probability.

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Bankroll sizing

Kelly Criterion

Review full or fractional Kelly sizing from your bankroll, price, and probability estimate.

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Value analysis

EV / Edge

Compare your probability estimate with the available price and calculate estimated EV.

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Balanced allocation

Arbitrage

Size every side of a compatible market and compare projected returns before costs.

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Risk management

Hedge

Estimate an opposing position and compare the projected result under either outcome.

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Promotions

Bonus Conversion

Estimate hedge sizing and conversion value for a stake-not-returned promotional credit.

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Market pricing

Implied Odds

Convert odds into implied probability—or probability back into equivalent odds.

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More math tools

Converters, market-margin checks, round robins, and sports models.

Market Pricing

Prediction Market

Convert a contract price into probability and odds, then estimate cost, payout, and profit after optional fees.

Market Pricing

Odds Converter

Convert prices between American, decimal, and fractional odds formats.

Market Pricing

Hold

Calculate the combined implied probability and margin in a two-sided market.

Market Pricing

Vig

Estimate the margin embedded in a two-sided market and compare each side's no-vig probability.

Payout & Risk

Round Robin

Count combinations and estimate total stake and payout ranges for round-robin entries.

Sports Models

Poisson

Estimate count-based outcome probabilities from an expected scoring average.

Sports Models

Half Point

Compare the estimated value of moving a spread by half a point at a different price.

Sports Models

Point Spread

Estimate a moneyline-equivalent price from a point spread and sport-specific assumptions.

A cleaner workflow

Move from price to position in order

01

Understand the price

Start with implied probability or the odds converter when you need to translate a quoted market price.

02

Estimate a fair baseline

Use no-vig, hold, or vig calculations to separate the quoted margin from a two-sided market.

03

Compare value and payout

Use EV, hedge, parlay, or bonus conversion once your price and probability assumptions are clear.

04

Review position size

Use Kelly only after deciding which probability estimate you trust and how much uncertainty you can accept.

Calculator questions

Which calculator should I use first?

Use implied probability or the odds converter to understand a quoted price. Use no-vig when you have both sides of a market. Move to expected value or Kelly only when you have a probability estimate you can explain.

Are Monster.bet calculators free?

Yes. The calculators in this library are public and free to use for educational and decision-support purposes.

Do calculator results predict what will happen?

No. Calculators apply formulas to the inputs you provide. They do not verify your probability assumptions, guarantee an outcome, or replace checking the current market and partner rules.

Can I use these for prediction markets?

Yes, when the calculator’s inputs match the contract structure. A price such as 62¢ can be read as a 0.62 decimal probability input, while payout, fees, and settlement rules still need to be checked on the platform.