Three Alphabets, One Number
Every sportsbook price is written in one of three formats — decimal, American (moneyline), or fractional — different notations for the same underlying probability. Canadian-facing operators mostly default to decimal, the format used across the rest of the world, but American odds show up constantly thanks to U.S. sportsbook influence. Fractional odds are rarer online in Canada but still appear on horse racing and legacy British-style markets. None of the three changes the bet — just how the same payout is written down.
How Each Format Actually Works
Decimal odds show your total return per $1 staked, including your stake: odds of 2.50 mean a $10 bet returns $25 total — $15 winnings plus your $10 back. American odds use a plus or minus number keyed to $100: -150 is how much you’d stake to win $100; +200 is how much a $100 stake would win. Fractional odds, written like 5/2, show profit relative to your stake — $2 at 5/2 wins $5 profit, plus your $2 back.
Converting Between Formats and Reading Implied Probability
Every price also implies a probability — the sportsbook’s built-in estimate of how likely that outcome is. For decimal odds, implied probability is 1 divided by the decimal price: a price of 2.00 implies a 50% chance; 1.33 implies roughly 75%. That’s the building block for understanding the vig, covered next.
| Decimal | American | Fractional | Implied Probability |
|---|---|---|---|
| 1.50 | -200 | 1/2 | 66.7% |
| 1.91 | -110 | 10/11 | 52.4% |
| 2.00 | +100 | 1/1 | 50.0% |
| 2.50 | +150 | 3/2 | 40.0% |
| 4.00 | +300 | 3/1 | 25.0% |
Try It: Live Odds Converter
Drag the slider and watch all three formats — plus the implied probability — update together.
The Vig: Why a Two-Sided Market Never Adds Up to 100%
Add up the implied probability of both sides of a standard two-way market and the total is always a little over 100% — that extra sliver is the vig, also called the overround or juice, and it’s how the sportsbook builds in a margin regardless of who wins. A textbook example: a spread market priced -110 on both sides implies 52.4% per side, or 104.8% combined, a roughly 4.8% overround. That’s not a hidden fee, just the structural cost of betting through a bookmaker. Vig size varies by market and sportsbook; lower-vig markets are better value.
Why Odds Move Before an Event Starts
Prices shift constantly between when a market opens and when the event starts, for two reasons: new information (a lineup change, an injury report, weather at an outdoor venue) shifts a sportsbook’s model of who’s likely to win, and money itself — sportsbooks adjust prices as bettors wager, shortening the price on a side attracting heavy action and lengthening the other, to manage risk and keep both sides balanced. That’s why “closing line” prices are often treated as the sharpest, most information-complete version of a market.
Putting the Format Together With a Real Bet Type
Odds notation is the vocabulary; the bet types built on it are where the real decisions happen. A straight bet on who wins outright is a moneyline bet, a bet on margin of victory is point spread betting, and bundling several bets into one ticket is a parlay. Sportsbooks such as Bet365 ↗ and BetMGM ↗ let you toggle the display format in account settings — a good way to practice converting between them. Remember the vig means the sportsbook has a structural edge on every market; our responsible gambling page has free tools if wagering starts feeling less like entertainment.