Implied Probability Explained

The formula for American odds

US sportsbooks quote moneyline and spread prices in American odds — a plus or minus number. The conversion to implied probability depends on the sign.

For negative odds (favorites, e.g. -150): implied probability = (−odds) / (−odds + 100) So -150 = 150 / (150 + 100) = 150 / 250 = 0.60, or 60%.

For positive odds (underdogs, e.g. +130): implied probability = 100 / (odds + 100) So +130 = 100 / (130 + 100) = 100 / 230 = 0.435, or 43.5%.

A couple of reference points worth memorizing: - -110 = 110 / 210 = 52.4% - +100 (even money) = 50.0% - -200 = 66.7% - +200 = 33.3%

Once a line is a percentage, it stops being an abstract number. If you think a road underdog wins closer to 48% of the time but the book prices them at +130 (43.5%), that gap is your edge.

Decimal and fractional odds

You'll run into decimal odds on international soccer markets — Serie A, Ligue 1, the Champions League — and some sportsbook apps let you switch the display.

Decimal odds: implied probability = 1 / decimal odds So 2.50 = 1 / 2.50 = 0.40, or 40%. Odds of 1.91 (the decimal equivalent of -110) = 1 / 1.91 = 52.4%.

Fractional odds: implied probability = denominator / (denominator + numerator) So 6/4 = 4 / (4 + 6) = 4 / 10 = 40%. Even money (1/1) = 50%.

All three formats describe the same thing. -110, 1.91 and 10/11 are identical prices and all resolve to 52.4%. Converting to a percentage is the fastest way to compare a moneyline on an NHL game against a decimal price on a Champions League match.

A worked NFL example with the vig

Take a typical NFL point spread. Both sides are priced at -110:

• Team A -3.5 at -110 → 52.4%
• Team B +3.5 at -110 → 52.4%

Add them: 52.4% + 52.4% = 104.8%.

A fair market would total exactly 100%. The extra 4.8% is the vig (also called the juice, the hold or the overround) — the sportsbook's built-in margin. That's why you can't just bet both sides and break even.

To find the true, vig-free probability, divide each side by the total: - Team A: 52.4 / 104.8 = 50.0% - Team B: 52.4 / 104.8 = 50.0%

Now a moneyline example that isn't 50/50. Say an MLB game is priced: - Favorite -175 → 175 / 275 = 63.6% - Underdog +150 → 100 / 250 = 40.0%

Raw total: 63.6% + 40.0% = 103.6%, so the vig is 3.6%. Vig-free: favorite 63.6 / 103.6 = 61.4%, underdog 40.0 / 103.6 = 38.6%.

The no-vig line is what you actually compare your own estimate against. If your model says the underdog wins 42% of the time and the fair price implies 38.6%, the +150 is a bet worth making.

Why lower margins matter when you compare books

The vig is the reason line shopping pays. A book that charges 4.2% margin returns more of your stake over time than one charging 5.3% on the same games — even if both display the same headline odds on your team.

From our sampled US pricing data, average two-way margin varies meaningfully across books: - FanDuel: 4.46% average margin (596 markets sampled) - DraftKings: 4.25% (1,068 sampled) - Fanatics Sportsbook: 4.25% (466 sampled) - Caesars Sportsbook: 5.27% (906 sampled) - BetMGM: 5.21% (438 sampled) - BetRivers: 6.35% (480 sampled)

A lower margin means the implied probabilities across a market add up closer to 100%, which means the price on your side is a little more generous. The best-price share metric tells the same story from the other direction: across sampled markets DraftKings held the best available price 54.0% of the time and Fanatics 41.8%, while BetMGM topped the price only 19.9% of the time.

These are pricing samples, not a guarantee of the number on any single game. But they're why converting odds to probability and checking two or three books before you tap the bet slip is the single most repeatable habit a bettor can build. Compare live numbers on our betting odds page before committing.

Turning implied probability into a bet decision

The workflow is short:

1. Convert the line to implied probability using the formulas above. 2. Add both sides and note the total — that's your vig check. 3. Divide each side by the total to get the no-vig (fair) probability. 4. Compare the fair probability to your own estimate of the game. 5. If your estimate of a side is higher than the book's fair probability, there's value in that price.

Example: a Champions League match has the home side at +145 (40.8% raw) and you've assessed them at around 46% to win. Even after stripping vig, the book's fair number will sit below your 46%, so the price is in your favor. That gap — your number versus the implied number — is the entire game.

One caution: implied probability tells you what a price says, not whether the price is right. The book's number reflects sharp money and information you may not have. Treat your own estimate honestly, and don't assume every gap is real edge.

Where implied probability shows up across US sports

The math is identical whether you're pricing an NFL spread, an NBA moneyline, an NHL puck line, a UFC fight or a golf outright — only the format and the number of outcomes change.

Two-way markets (spreads, totals, most moneylines) add up to roughly 100% plus the vig. Multi-way markets — a UFC card with several fighters listed, a golf tournament with 150 names, or an outright futures market — will add up to a much larger overround because there are more outcomes for the book to margin. That's normal; the more selections, the more implied probabilities stack above 100%.

For futures especially, converting every price to a percentage is the only way to see how much juice is buried in a long list. Browse current futures odds and market movers to see how implied probabilities shift as money comes in and news breaks.