@rich-apis/polymarket-odds

Convert Polymarket probabilities to decimal, fractional, and American odds formats. Zero dependencies, pure JavaScript.

Part of the PolySignals toolkit for Polymarket analytics. See also: @rich-apis/polymarket-sdk

Install

npm install @rich-apis/polymarket-odds

Usage

const odds = require('@rich-apis/polymarket-odds');

// Polymarket shows "Yes" at 65% probability
const result = odds.convert(0.65);
console.log(result);
// {
//   decimal: 1.5385,
//   fractional: "7/13",
//   american: -186,
//   impliedProbability: 0.65
// }

// Individual conversions
odds.toDecimal(0.65);    // 1.5385
odds.toFractional(0.65); // "7/13"
odds.toAmerican(0.65);   // -186

// Convert back to probability
odds.fromDecimal(2.0);      // 0.5
odds.fromAmerican(-150);    // 0.6

API

convert(probability) → { decimal, fractional, american, impliedProbability }

All-in-one conversion. Takes a probability between 0 (exclusive) and 1 (inclusive).

toDecimal(probability) → number

Returns decimal odds (e.g. 1.5385). Standard in Europe and exchanges.

toFractional(probability) → string

Returns fractional odds as a string (e.g. "3/2"). Standard in the UK.

toAmerican(probability) → number

Returns American/moneyline odds (e.g. -186 or +233). Standard in the US.

• Negative = favourite (bet that much to win $100)
• Positive = underdog (win that much on a $100 bet)

fromDecimal(decimalOdds) → number

Convert decimal odds back to implied probability.

fromAmerican(americanOdds) → number

Convert American odds back to implied probability.

Why?

Polymarket displays probabilities as percentages (e.g. 65%), but many traders think in odds formats they already know from sports betting. This tiny utility bridges that gap.

Related

• PolySignals Whale Bot - Real-time Polymarket whale movement alerts
• @rich-apis/polymarket-sdk - Full Polymarket API client (coming soon)

License

MIT