The Three Odds Formats: American, Decimal, and Fractional
Every sportsbook displays odds in at least one of three formats. Ontario books default to American odds but most allow you to switch. Understanding all three lets you compare lines across platforms quickly.
Negative numbers show how much you risk to win $100. Positive numbers show how much you win on a $100 stake. Standard at all Ontario books. The most common format in North America.
Positive: risk $100, win $150
Your total return per $1 staked, including your stake. Decimal 1.91 equals American -110. Common in Europe and on Pinnacle. Easiest format for quick expected value calculations.
$100 x 1.91 = $191 total ($91 profit)
Shows profit relative to stake. 10/11 means win $10 for every $11 risked. Common in UK markets. Less intuitive for North American bettors but you will encounter it on horse racing boards.
(3/2) x $100 = $150 profit
| American | Decimal | Fractional | Implied probability | Common context |
|---|---|---|---|---|
| -110 | 1.909 | 10/11 | 52.38% | Standard spread/total |
| -104 | 1.962 | 25/26 | 50.97% | Pinnacle totals |
| -145 | 1.690 | 20/29 | 59.18% | Moderate favourite ML |
| +125 | 2.250 | 5/4 | 44.44% | Moderate underdog ML |
| +200 | 3.000 | 2/1 | 33.33% | Heavy underdog |
| -200 | 1.500 | 1/2 | 66.67% | Heavy favourite |
Implied Probability: The Number Inside Every Odd
Every set of odds contains an implied probability. This is the win percentage the book is pricing in for that outcome. Being able to calculate it instantly is the single most important mathematical skill in sports betting.
Vig (Juice): What the Book Takes on Every Bet
Vig is the book's built-in commission. It is why the house always has a mathematical advantage regardless of which side wins. Understanding exactly how it works is non-negotiable for serious bettors.
Value Betting: When Odds Are Wrong
A value bet is any bet where your assessed probability of the outcome is higher than the book's implied probability. This is the entire intellectual foundation of profitable sports betting.
Step 1: Convert the odds to implied probability using the formulas above. Step 2: Form your own estimate of the true probability of the outcome. Step 3: If your estimate is meaningfully higher than the implied probability, you have a value bet. The book is underpricing the outcome relative to what you believe the true odds are. This is the only mathematically sound reason to place any bet.
Book offers +150 on Team A. Your model says Team A wins 45% of the time.
Book offers -145 on Team B. You think Team B wins 58% of the time.
Book offers -110 on Team C. You think Team C wins 53% of the time.
Line Shopping: Getting the Best Price on Every Bet
Different Ontario books post different odds on the same game. Shopping for the best number is the lowest-effort, highest-return habit any bettor can develop. It requires no handicapping ability whatsoever.
Payout Maths You Should Know Cold
These are the numbers every experienced bettor has memorised. You should not need to calculate these mid-session.
Six Odds Mistakes Canadian Bettors Make Constantly
Higher odds just mean lower implied probability. +400 is not a "better" bet than -110. Whether either bet is good depends entirely on whether the true probability exceeds the implied probability. A -200 favourite can be a great value bet. A +400 underdog can be terrible value. The odds themselves tell you nothing about value.
When Book A offers -110 and Book B offers -104 on the same side of the same game, most bettors do not notice. They bet at whichever book they opened first. The -104 at Pinnacle requires a 50.97% win rate to break even. The -110 requires 52.38%. Over 200 bets that 1.41% difference compounds into a substantial bankroll difference.
Knowing that -145 implies 59.18% tells you nothing about whether to bet without an independent estimate of the true probability. Bettors who skip this step and simply bet because odds "look good" are gambling, not betting. The only valid reason to bet is a genuine belief that true probability exceeds implied probability.
In NFL betting, the difference between -2.5 and -3 is not 0.5 points. It is the most common winning margin in the sport. Half-point differences around key numbers (3, 7 in NFL; 1 goal in NHL) are worth significant expected value. Never treat half points as cosmetic.
A bettor comparing American -110 at one book with decimal 1.87 at another without converting is operating blind. These are different prices: -110 = decimal 1.909. The 1.87 book is actually offering worse odds. Always convert to the same format before comparing lines across platforms.
The public consistently over-bets favourites. Books shade favourite lines to account for this. The result is that underdogs are systematically underpriced in markets with high recreational volume. Heavy public favourite lines are frequently poor value. The favourite is not smart money by definition - it is often the most expensively priced side on the board.