Guide

How implied probability works

Odds are prices. Implied probability is the break-even frequency encoded by that price, before you decide whether the price is informative or fair.

Reviewed

From price to probability

American odds describe profit relative to a $100 reference. Positive odds show the profit on a $100 stake; negative odds show the stake required to win $100. Decimal odds show the total return for each unit staked. Each can be converted to the same probability scale.

For +150, the formula is 100 / (150 + 100), or 40%. For -150, it is 150 / (150 + 100), or 60%. Decimal 2.50 is 1 / 2.50, also 40%.

Break-even is not a forecast

If you repeatedly accepted +150 on independent events, ignoring practical costs, you would need to win 40% of them to break even. That statement describes the price. It does not establish that a specific event has a 40% real-world chance. To make that claim, you need a separate, well-calibrated estimate and matching settlement rules.

Why markets exceed 100%

Convert both sides of a typical market and the probabilities usually sum above 100%. Two sides at -110 imply 52.38% each, totaling 104.76%. The excess is the sportsbook's displayed margin under a simple proportional interpretation. Comparing one raw side directly with a normalized probability mixes two different scales.

Common mistakes

  • Treating 60% as certainty. It still implies failure four times in ten.
  • Ignoring vig when comparing opposite sides of one market.
  • Comparing prices from different timestamps after news has moved the market.
  • Mixing markets with different overtime or settlement rules.
  • Assuming a shorter price always means a better opportunity; price and probability must be assessed together.

A reproducible workflow

  1. Record the exact market, price, sportsbook, and timestamp.
  2. Convert every mutually exclusive outcome to raw implied probability.
  3. Inspect the total overround and normalize if a no-vig estimate is required.
  4. Keep the raw price and normalized estimate separately labeled.
  5. State uncertainty and avoid turning a distribution into a guarantee.

Try the arithmetic in the implied-probability calculator, then normalize a two-way market with the no-vig calculator.