Implied Probability Explained

The formula: American odds to implied probability

American odds split into two cases.

• Negative odds (favorites): implied probability = (−odds) / (−odds + 100). For −150: 150 / 250 = 0.60 = 60%.
• Positive odds (underdogs): implied probability = 100 / (odds + 100). For +150: 100 / 250 = 0.40 = 40%.

A few reference points worth memorizing:

• −110 → 110 / 210 = 52.38%
• −200 → 200 / 300 = 66.67%
• +100 (even money) → 100 / 200 = 50.00%
• +250 → 100 / 350 = 28.57%

The −110 case is the standard price on point spreads and totals across bet365, DraftKings, FanDuel, BetMGM, Caesars and every other US sportsbook. Notice it implies 52.38%, not 50% — that gap is where the house edge lives.

Decimal and fractional odds convert the same way

Most US books display American odds by default, but many let you switch to decimal, and futures markets sometimes surface fractional prices.

• Decimal odds: implied probability = 1 / decimal. Decimal 1.91 → 1 / 1.91 = 52.36%. Decimal 2.50 → 40%.
• Fractional odds: implied probability = denominator / (numerator + denominator). 6/4 → 4 / 10 = 40%. 10/11 → 11 / 21 = 52.38%.

All three formats describe the same market. −110, decimal 1.91 and 10/11 are effectively identical prices. Converting to implied probability is the neutral common language that lets you compare a spread line at one book against a decimal price at another.

Why the percentages add up to more than 100%

Add the two implied probabilities on a two-way market and you rarely get 100%. Take a point spread priced −110 / −110:

• Side A: 52.38%
• Side B: 52.38%
• Total: 104.76%

That extra 4.76% is the overround — the bookmaker's built-in margin, commonly called the vig or juice. It is the sum of implied probabilities minus 100%. On a two-way −110/−110 market the vig is about 4.55% expressed as a margin, or 4.76% as the raw overround. Either way, the book prices the two sides so their probabilities sum above 100%, guaranteeing a theoretical edge regardless of outcome.

The higher the sum, the more the book is charging. That's the single most useful number when comparing where to place a bet.

Removing the vig to find true probability

The raw implied probability includes the book's margin, so it overstates the real chance. To strip it out, divide each side's implied probability by the total.

Worked example, a moneyline priced −150 / +130:

• Favorite −150 → 150 / 250 = 60.00%
• Underdog +130 → 100 / 230 = 43.48%
• Sum = 103.48% (a 3.48% overround)

No-vig probabilities:

• Favorite: 60.00 / 103.48 = 57.98%
• Underdog: 43.48 / 103.48 = 42.02%

The favorite's "true" implied probability is closer to 58%, not 60%. If your own model puts the favorite at 62%, the market's 58% no-vig line gives you an edge. If your model says 55%, the market is pricing the favorite too high for you.

This two-step process — convert, then de-vig — is the core of finding value. The no-vig line is also the fairest single estimate of the real probability a sharp market is offering.

Turning probability into expected value

Implied probability lets you calculate expected value (EV) on any bet. EV per $100 staked = (your probability × profit if win) − (probability of loss × stake).

Example: a book offers +130 (implied 43.48%). You estimate the true chance at 48%.

• Profit if win at +130 on $100 = $130
• EV = (0.48 × $130) − (0.52 × $100) = $62.40 − $52.00 = +$10.40 per $100

A positive number means the bet is +EV at that price. Because +130 only needs you to be right 43.48% of the time to break even, your 48% estimate clears the bar comfortably. Flip it: if you thought the true chance was only 42%, the same +130 price would be −EV, and you'd pass.

The break-even win rate for any price is simply its implied probability. That's why memorizing that −110 requires 52.38% is so useful — it's the hit rate you need just to break even on standard spreads and totals.

Margins differ by sportsbook — and that changes the true line

The lower a book's margin, the closer its posted odds sit to the true probability, and the better the price you get. BETAXIO price sampling across US sportsbooks shows meaningful gaps in average margin:

• FanDuel: 4.46% average margin (596 markets sampled), best-price share 36.1%
• DraftKings: 4.25% average margin (1,068 sampled), best-price share 54.0%
• Fanatics Sportsbook: 4.25% average margin (466 sampled), best-price share 41.8%
• Caesars Sportsbook: 5.27% average margin (906 sampled), best-price share 36.2%
• BetMGM: 5.21% average margin (438 sampled), best-price share 19.9%
• BetRivers: 6.35% average margin (480 sampled), best-price share 28.3%

DraftKings and Fanatics post the tightest average margins in the sample at 4.25%, and DraftKings tops the best-price share at 54.0% — meaning it offered the highest available price on more than half the markets sampled. A 4.25% margin versus a 6.35% margin is roughly two extra percentage points of overround baked into every line at the wider book, which directly raises the break-even hit rate you need to profit.

Editorial read: for line shopping, the tightest-margin books (DraftKings, Fanatics, FanDuel) give you a de-vigged line nearest the true probability. Wider-margin books like BetRivers and BetMGM require a larger edge to overcome the extra juice. Note: bet365, ESPN BET and Hard Rock Bet are not included here because no margin sample was available; their odds ratings (bet365 8.8, ESPN BET 7.3, Hard Rock Bet 7.3) reflect broader scoring, not this margin study.

Using implied probability for line shopping

Because margins vary, the same game can carry different implied probabilities at different books. Convert each side to no-vig probability and the operator with the lowest de-vigged number on your side is giving you the longest true price.

A practical routine:

• Pull the price for your outcome at two or three books.
• Convert each to implied probability.
• De-vig each market by dividing by the two-way total.
• Bet where the no-vig implied probability of your side is lowest — that's the best price.

With DraftKings holding the top best-price share in the sample (54.0%), it's frequently the book to beat, but no single operator wins every market. That's the entire argument for shopping lines rather than betting one book. See live prices on the odds page and track how numbers move on market movers.