A Guide to Odds

Odds do two jobs at once. They tell you what a bet pays, and they hint at how likely the bookmaker thinks the outcome is. Learn to read both and most betting markets stop looking mysterious. This page is for adults aged 18 and over.

Three ways to write the same price

The same bet can be shown in three formats. They describe the same thing.

Decimal

Multiply your stake by the number. The result is your total return, stake included. Easiest to compare at a glance.

Fractional

The first number is profit, the second is stake. At 4/1 you win 4 for every 1 you bet, plus your stake back.

American

A plus sign shows the profit on a 100 stake. A minus sign shows what you must stake to make 100 profit. So +200 pays 200 on 100, and -200 needs 200 staked to win 100.

From price to chance

Any price can be turned into an implied probability. With decimal odds the sum is simple:

Implied probability = 1 ÷ decimal odds

• 2.00 means 1 ÷ 2 = 50%.
• 4.00 means 1 ÷ 4 = 25%.
• 1.25 means 1 ÷ 1.25 = 80%.

This is the chance the price suggests, not the true chance. Nobody knows the true chance of a football match. The price is the bookmaker's estimate, adjusted for how money is coming in, with a margin added.

Where the margin hides

Add up the implied probabilities for every outcome in a market. In a fair world they would total exactly 100%. They never do.

Take a match with three outcomes priced at 2.40 for the home win, 3.30 for the draw and 3.00 for the away win:

• 1 ÷ 2.40 is about 41.7%
• 1 ÷ 3.30 is about 30.3%
• 1 ÷ 3.00 is about 33.3%

Total: about 105.3%. That extra 5.3% is the overround. It is how the bookmaker builds in its profit. The higher the total, the more you pay for each bet.

What odds cannot tell you

• They do not tell you who will win. Favourites lose all the time.
• Short odds are not "safe". A price of 1.20 still loses about one time in six, on its own terms.
• Long odds are not "value" just because the payout looks big.
• A price that moves does not mean someone knows the result.

Casino games use odds too

A casino payout is a price as well. When a game pays slightly less than the true odds of a bet, the gap is the house edge. The same idea runs through a sportsbook margin and a slot's return to player. For a walk through live markets, see our piece on using live scores for in-play betting.

Before you bet

Understanding odds helps you see the price. It does not make a bet profitable. Betting is for adults only, the rules differ widely between countries, and some places ban online betting. Check the rules where you live, and set a limit first using the steps on Setting Limits.