# Implied Probability Calculator

Free implied probability calculator. Convert American, decimal, or fractional betting odds to implied probability. Find value bets by comparing to true probability.

## What this calculates

Convert betting odds from any format to implied probability. Enter American, decimal, or fractional odds to see the bookmaker's implied probability of the outcome, plus conversions to all three formats.

## Inputs

- **Odds Format** — options: American (e.g., -150 or +200), Decimal (e.g., 2.50), Fractional (numerator/denominator) — Select the format of your betting odds.
- **American Odds** — Negative for favorites (e.g., -150), positive for underdogs (e.g., +200).
- **Decimal Odds** — min 1.01 — Decimal odds (must be greater than 1.00).
- **Fractional Odds (Numerator)** — min 1 — The numerator of the fractional odds (e.g., 3 in 3/1).
- **Fractional Odds (Denominator)** — min 1 — The denominator of the fractional odds (e.g., 1 in 3/1).

## Outputs

- **Implied Probability** — formatted as percentage — The implied probability from the given odds.
- **American Odds** — formatted as text — The odds in American format.
- **Decimal Odds** — The odds in decimal format.
- **Fractional Odds** — formatted as text — The odds in fractional format (approximate).
- **Payout on $100 Bet** — Total payout (stake + profit) on a $100 wager.
- **Breakdown** — formatted as text — Step-by-step conversion.

## Details

Every set of betting odds implies a probability. Understanding implied probability helps you compare odds across sportsbooks and spot value bets where the true probability exceeds what the odds suggest.

**Conversion Formulas:**

**American to probability:**
- Negative odds (favorite): p = |odds| / (|odds| + 100)
- Positive odds (underdog): p = 100 / (odds + 100)

**Decimal to probability:**
- p = 1 / decimal odds

**Fractional to probability:**
- p = denominator / (numerator + denominator)

**Example:** American odds of -150 mean the bookmaker implies a 60% chance. If your analysis says the true probability is 65%, that is a value bet. If you think it is only 55%, the odds are not in your favor.

**What About the Vig?**

Bookmakers build in a margin (the "vig" or "juice"). When you add the implied probabilities of all outcomes in a market, the total exceeds 100%. The excess is the bookmaker's edge. To find the "fair" probability, divide each implied probability by the total of all outcomes.

## Frequently Asked Questions

**Q: What is the difference between implied and true probability?**

A: Implied probability is what the betting odds suggest the chance of an outcome is. True probability is the actual likelihood of the event happening. If implied probability is lower than true probability, you have a value bet. The gap between the two (plus the vig) is how bookmakers make money.

**Q: Why do implied probabilities from all outcomes add up to more than 100%?**

A: The excess over 100% is the bookmaker's margin (vig or overround). For example, a coin flip might be priced at -110 on both sides. Each side implies 52.4% probability, totaling 104.8%. That extra 4.8% is the bookmaker's built-in edge. To get 'no-vig' probabilities, divide each by the total.

**Q: How do I convert between American, decimal, and fractional odds?**

A: Start with decimal odds as the common base. American to decimal: if negative, decimal = (100/|odds|) + 1; if positive, decimal = (odds/100) + 1. Fractional to decimal: decimal = (numerator/denominator) + 1. Decimal to American: if >= 2.00, American = +(decimal-1)*100; if < 2.00, American = -100/(decimal-1).

---

Source: https://vastcalc.com/calculators/statistics/implied-probability
Category: Statistics
Last updated: 2026-04-08