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How to read odds

Odds are a price, and every price is a chance in disguise. Here is how to read any line in a minute, with worked examples.

The short version

Odds are a price. Every price can be turned into a chance: the share of the time a bet at that price has to win just to break even. A favourite at −150 needs to win 60.0% of the time; an underdog at +130 needs 43.5%.

Add both sides and you get more than 100% (103.5% here). The extra 3.5% is the margin the price-setter keeps. Take it out and you get each side's fair chance: 58.0% and 42.0%. That fair chance is the "market's chance" SportLark shows on a game.

Three ways to write the same price

American odds (common in the US and Canada) are written around $100. A minus sign marks the favourite and says how much you risk to win $100; a plus sign marks the underdog and says how much $100 wins.

Decimal odds (common in Europe and Australia) are the total you get back for each $1 staked, stake included. Fractional odds (common in the UK and Ireland) are the profit over the stake.

  • +150 American = 2.50 decimal = 3/2 fractional. A $10 bet wins $15 and returns $25.
  • −150 American = 1.67 decimal = 2/3 fractional. A $30 bet wins $20.00 and returns $50.00.
  • +100 American = 2.00 decimal = Evens ("even money"). A $10 bet wins $10.

Turning a price into a chance

The chance a price implies is the break-even rate. For decimal odds it is simply 1 ÷ the price. For American odds:

  • Minus price: risk ÷ (risk + 100). −150 → 150 ÷ 250 = 60.0%.
  • Plus price: 100 ÷ (price + 100). +130 → 100 ÷ 230 = 43.5%.
  • Decimal: 1 ÷ price. 2.50 → 40.0%.

The margin, and the fair chance

Prices are set so both sides add up to more than 100%. In the example above the two sides add to 103.5%, so the margin is 3.5%. That margin is why betting both sides of the same game loses money over time.

To read what the market really thinks, scale both sides back to 100%: 60.0% ÷ 103.5% = 58.0% for the favourite and 42.0% for the underdog. SportLark takes the margin out this way before it shows any market chance, so the two sides of a game always add to 100%.

The main markets

Most games are priced three ways. The same chance-and-margin reading works for all of them.

  • Moneyline: who wins the game. In hockey and baseball this usually includes overtime or extra innings; check the market's rules.
  • Spread: the favourite must win by more than a set number of points, or the underdog must not lose by more than it. In hockey it is called the puck line (usually 1.5 goals) and in baseball the run line (usually 1.5 runs).
  • Total (over/under): the two teams' combined score, over or under a set number such as 6.5 goals or 221.5 points.
  • Parlay: several bets joined into one. Every leg must win. The prices multiply, so the chance of the whole ticket falls fast: three legs at 60% each win together only about 22% of the time.
  • Props: bets on one player or one event inside a game (a player's points, the first goal).

Why prices move

A line opens, then moves as news and money arrive: an injury, a starting goalie or pitcher being named, the weather, or simply more money on one side. The last price before the game starts is the closing line. A moving line is the market changing its mind, not a signal on its own.

How SportLark reads a game

Every game shows each side's win chance. Where a sport is shown as a market view, that chance is the market's fair chance with the margin taken out. Where we run our own model, its forecast is blended with the market and calibrated, so a 60% is meant to come true about 6 times in 10.

When our chance clearly beats what the price needs, the game shows a lean (Strong or Slight); when it does not, it says No lean. Most games have no lean, and that is the honest answer when the numbers agree with the market.

Forecasts are chances, not promises. A 70% side loses about three times in ten, and nothing on the site is a guarantee or financial advice.

Play it safe

SportLark shows scores, odds and model forecasts for information only. It does not take bets or handle money. If you bet elsewhere, you must be 21+ (or the legal age where you are) and betting must be legal where you live. If gambling stops being fun, call 1-800-GAMBLER.

Questions

What does −150 mean?
−150 marks the favourite: you risk $150 to win $100. The price implies a 60.0% chance, which is how often it has to win to break even.
What does +130 mean?
+130 marks the underdog: $100 wins $130. The price implies a 43.5% chance.
How do I convert odds to a percentage?
For a minus price, divide the number by itself plus 100 (−150 → 150 ÷ 250 = 60%). For a plus price, divide 100 by the number plus 100 (+130 → 100 ÷ 230 = 43.5%). For decimal odds, divide 1 by the price.
Why do both sides add up to more than 100%?
The price-setter builds in a margin (also called the vig or juice). In a −150 / +130 game the sides add to 103.5%, a 3.5% margin. Scale both back to 100% to get each side's fair chance.
What is the puck line or run line?
It is the spread in hockey and baseball: usually 1.5 goals or runs. The favourite at −1.5 must win by two or more; the underdog at +1.5 covers if it wins or loses by one.
Can I place bets on SportLark?
No. SportLark shows scores, odds and win chances for information only. It does not take bets or handle money.
Are the win chances guaranteed?
No. They are forecasts. A side shown at 70% is expected to lose about three games in ten.

Try it

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