Odds Converter

Every conversion the tool performs reduces to a handful of formulas. Worked through for the two most common NFL prices:

• −110 (standard spread price). Decimal = 1 + 100/110 = 1.909. Fractional = 100/110 = 10/11. Implied probability = 110/(110+100) = 52.38%.
• +150 (a modest underdog). Decimal = 1 + 150/100 = 2.50. Fractional = 3/2. Implied probability = 100/(150+100) = 40.0%.

Going the other way: a decimal price d converts to American as −100/(d−1) when d < 2.00, or +100×(d−1) when d ≥ 2.00. So 1.909 → −100/0.909 = −110, and 2.50 → +150. Decimal is the cleanest format for compounding: a two-leg parlay of 1.909 and 2.50 pays 1.909 × 2.50 = 4.773, which is +377 in American terms. All exact formula math.

One habit worth building: think in implied probability, not in payouts. “−110” is the book saying “this happens 52.4% of the time.” Whether you agree is the entire bet.

Implied probabilities across both sides of a market add up to more than 100% — the excess is the book's margin. To see the market's actual opinion, normalize it away:

The 3.48-point overround is the price of playing. On a standard −110/−110 spread market the sum is 104.76%, and the no-vig probabilities are exactly 50/50 — the book is not predicting the favorite covers more often, it is charging you either way. Exact formula math throughout.

Converting odds tells you the bar; the bundled game log tells you how hard the bar is to clear. Across 7,276 completed NFL games from 1999–2025, neither side of the spread market comes close to the 52.38% needed at −110:

Data: nflverse games.csv bundled with this site (7,276 completed games, 1999–2025), computed by the author. Underdogs are the mirror image of favorites.

A useful exercise once conversions feel comfortable: translate an entire game listing into probabilities and check that the numbers agree with each other. An illustrative board in current format — Ravens −3 (−110), moneyline −155 / +135, total 47.5 (−110 both ways):

• Spread: −110 each way converts to 52.4% / 52.4% — after removing the vig, the market calls the cover a coin flip, as always.
• Moneyline: −155 implies 60.8% (155/255); +135 implies 42.6%. Sum 103.3%, so the no-vig win probabilities are 58.8% and 41.2%.
• Cross-check against history: in the bundled nflverse game log, teams that closed as 3-point favorites won 58.0% of 1,153 games (1999–2025) — almost exactly what the no-vig moneyline says. A fair moneyline for a −3 favorite is therefore about −138; the −155 sticker is that fair price plus the book's margin.

Data: nflverse games.csv bundled with this site (7,276 completed games, 1999–2025), computed by the author; conversions are exact formula math.

This is the practical payoff of fluent odds reading: the spread, the moneyline, and 27 years of results all encode the same opinion, and you can audit any one of them against the other two before putting money behind a misread.

• Implied probability includes the book's margin. Raw conversion overstates every outcome's chance; use the no-vig calculation when you want the market's real opinion.
• The historical table is descriptive, not a system. It shows that label-based blind strategies lose to the juice; it does not say anything about a specific game.
• Overround varies by market. Main spreads run near 4.8%; props, futures, and parlays carry far more — conversions are exact, but the cost of playing is not constant.
• Rounding conventions differ. Books round decimal odds to two places and fractional odds to traditional ladders (10/11, 20/21), so small display differences between formats are usually rounding, not value. When comparing across books, compare implied probabilities, not display strings.