Implied Probability

Note

The app interface is in Spanish. This guide references the actual labels you will see.

The Implied Probability tool serves two purposes: it converts odds between the three major formats instantly, and it strips the sportsbook’s built-in margin (vig) to reveal the fair probability of an outcome. Use it whenever you need to translate odds or compare what a sportsbook thinks will happen versus what you think will happen.

This tool is available to all users at Tools > Implied Probability (/tools/implied-probability). All calculations run entirely in your browser.

Odds Converter

The top section displays a grid with four fields, all visible at once:

Field	Description
American Odds	Standard US format (e.g., -110, +150). Negative means favorite, positive means underdog.
Decimal Odds	European format (e.g., 1.91, 2.50). Represents total return per dollar wagered including the stake.
Fractional Odds	UK format (e.g., 5/1, 10/11). Two input fields separated by a / divider. Represents net profit relative to stake.
Implied Probability (%)	The win probability embedded in the odds. This field has an accent border to highlight it as the key output.

Editing any one of these four fields instantly updates the other three. You can work in whichever format you are most comfortable with and the tool handles all conversions.

De-Vig Calculator

Below the converter grid, a collapsible section labeled Show De-Vig Calculator lets you remove the sportsbook’s margin from a two-way market.

Enter both sides of the market:

Input	Description
Over / Yes Odds (American)	The American odds for the Over or Yes side of the market.
Under / No Odds (American)	The American odds for the Under or No side of the market.

The de-vig section produces three outputs:

Output	What It Means
Total Juice (Overround)	The sportsbook’s total margin on this market. For example, a 4.5% overround means the two implied probabilities sum to 104.5% instead of 100%.
Fair Over Probability	The true probability of the Over/Yes outcome after removing the vig.
Fair Under Probability	The true probability of the Under/No outcome after removing the vig.

How It Works

Odds conversion follows standard formulas between American, Decimal, and Fractional formats. All formats ultimately express the same thing: the ratio of profit to stake and the implied probability.

De-vig uses the multiplicative method:

Fair Probability = Raw Probability / (Raw Over Prob + Raw Under Prob)

For example, if a -110/-110 market gives raw probabilities of 52.38% each (summing to 104.76%), the fair probability for each side is 52.38 / 104.76 = 50.0%.

Tips

Use De-Vig to Find Fair Probabilities

Sportsbook odds always include a margin. A -110/-110 market looks like a coin flip, but the implied probabilities sum to 104.76%, not 100%. The de-vig calculator strips that margin so you can see the sportsbook’s true opinion of each outcome. Feed the fair probability into the EV Calculator for a more accurate expected value.

• When comparing odds across sportsbooks, convert everything to the same format first. Decimal is often the easiest for mental math.
• The overround percentage tells you how much the sportsbook is charging. Lower overround means a more competitive market. Standard player prop markets run around 4-6% overround.
• Implied probability from raw odds overstates the true chance of each outcome. Always de-vig before using the probability as an input for EV or Kelly calculations.
• Fractional odds are most common in UK markets. If you follow American sports, you will primarily work with American odds but may encounter Decimal from international books.