ODDS MATH
Informational tool only — not betting, financial, or legal advice. Market outcomes remain uncertain; no result is a guarantee.
-110 is the standard price on an NFL spread or total. As a decimal it is 1.9091, as a fraction 10/11, and it implies a 52.4% win probability — you have to win 52.4% of -110 bets just to break even. A +250 underdog is 3.50 decimal, 5/2 fractional, and 28.6% implied. The converter above opens on -110.
The honest part: implied probability is the break-even rate built into the price, vig included — not the true chance the bet wins. Add both sides of a real market and the implied probabilities total more than 100%; the excess is the book's margin.
WORKED EXAMPLE
The standard NFL spread price, -110, is 1.9091 in decimal and 10/11 in fractional, and it implies a 52.4% win probability: at -110 you risk $110 to win $100, so you must win 52.4% of those bets to break even. A +250 futures price — a mid-range longshot — is 3.50 decimal and 5/2 fractional, implies 28.6%, and turns a $100 stake into a $350 payout ($250 profit).
Every format is the same price in different clothes, and decimal is the hub. A negative American price says what you risk to win $100; a positive one says what you win on a $100 risk. Decimal odds are your total return per $1 staked, stake included. Fractional odds are profit over stake. The implied probability is 1 ÷ decimal odds — the break-even win rate at that price, with the book's margin still inside it.
AMERICAN → DECIMAL: -110 → 1 + 100/110 = 1.9091; +250 → 1 + 250/100 = 3.50. DECIMAL → AMERICAN: 3.50 → +(3.50 − 1) × 100 = +250; 1.9091 → −100 ÷ (1.9091 − 1) = −110. FRACTIONAL: decimal − 1 written as a fraction — 1.9091 → 10/11. IMPLIED PROBABILITY: 1 ÷ decimal — 1 ÷ 3.50 = 28.6%.
The honest part: implied probability is a break-even rate, not a forecast. Add the implied probabilities of both sides of a real market and they total more than 100% — the excess is the book’s margin (the vig). A price can convert perfectly and still be a bad price; conversion is arithmetic, not an edge.
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