Fundamentals
How betting odds work
Odds are just probability with a fee attached. Once you can convert a price into a percentage in your head, most betting advice becomes either obvious or obviously wrong.
The three formats
Decimal odds are the Canadian and European default. The number is your total return per dollar staked, stake included. A price of 2.50 returns $2.50 on a $1 bet, meaning $1.50 profit.
American odds use a plus or minus. A minus number is how much you must stake to win $100. Minus 150 means risk $150 to win $100. A plus number is how much you win from a $100 stake. Plus 130 means a $100 bet returns $130 profit.
Fractional odds, common in the UK and in horse racing, show profit over stake. 5/2 means five dollars profit for every two staked.
Turning a price into a probability
For decimal odds, divide 1 by the price. A price of 2.50 implies 1 / 2.50, or 40 percent. A price of 1.50 implies 66.7 percent.
For American odds on a favourite, the maths is the negative odds divided by that number plus 100. Minus 150 gives 150 / 250, or 60 percent. For an underdog, it is 100 divided by the odds plus 100. Plus 130 gives 100 / 230, or 43.5 percent.
This one calculation is the whole skill. If you think a team wins 50 percent of the time and the book is offering 2.20, that is a bet worth making. If the book is offering 1.80, it is not, no matter how confident you feel.
Where the vig lives
Add the implied probabilities of both sides of a market and you will get more than 100 percent. A standard football spread priced at minus 110 on both sides implies 52.4 percent each, totalling 104.8 percent. That 4.8 points is the book’s margin, called the vig, juice or overround.
It means a coin flip market requires you to win about 52.4 percent of the time just to break even. That is the hurdle. Everything else is detail.
Why line shopping is the only free money in betting
Books disagree. One might have a total at 6 and another at 6.5 on the same hockey game. Taking the better side of that disagreement costs nothing and compounds over hundreds of bets.
This is the strongest practical argument for holding two or three accounts. In thin markets like the CFL, where fewer books set numbers, the disagreements are larger.
Common questions
What do plus and minus mean in betting odds?
Minus indicates a favourite and tells you how much you must stake to win $100. Plus indicates an underdog and tells you how much profit a $100 stake returns.
How do I convert decimal odds to a probability?
Divide 1 by the decimal price. A price of 4.00 implies a 25 percent chance. A price of 1.25 implies 80 percent.
What is the vig and how much is it?
The vig is the sportsbook’s built-in margin. On a standard two-way market priced at minus 110 both sides, it is about 4.8 percent, meaning you need to win roughly 52.4 percent of your bets to break even.
Before you deposit anywhere
Set a deposit limit the day you open an account, not the day you need one. Every regulated Canadian sportsbook has limit and self-exclusion tools built in, and the provincial help lines on our responsible gambling page are free and confidential.