Betting odds explained: decimal, fractional and American
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Odds are the language of betting. They tell you two things at once: how much a successful bet pays, and how likely the bookmaker thinks the outcome is. Once you can read them in any format, every other topic in betting becomes easier to follow.
What odds actually describe
A team priced at 2.00 to win is, according to the price, about as likely to win as to not win. A team priced at 10.00 is considered a long shot. The price is not a prediction that something will happen. It is the payout rate for taking the risk, adjusted by the bookmaker's margin.
Decimal odds
Decimal odds are the most common format in Europe, Australia and Canada, and they are the easiest to use. The number is what you get back for every unit you stake, including your stake.
- Stake 10 at 2.50: the return is 25, of which 15 is profit.
- Stake 10 at 1.50: the return is 15, of which 5 is profit.
The formula is simply return = stake x odds, and profit = return - stake. Decimal odds are always above 1.00, because a price of 1.00 would return only your own stake.
Fractional odds
Fractional odds are traditional in the United Kingdom and Ireland, especially for horse racing. A price of 5/2 (read "five to two") means you win 5 for every 2 staked, so profit = stake x 5 / 2. Stake 10 and you win 25 profit, for a total return of 35.
Two quick rules help. When the first number is bigger than the second (5/2), the selection is the underdog and pays more than your stake. When it is smaller (2/5), the selection is the favourite and the profit is less than the stake. "Evens" or 1/1 means profit equals stake.
American (moneyline) odds
American odds use a positive or negative number around a base of 100.
- A positive number such as +150 shows the profit on a 100 stake: stake 100 and win 150.
- A negative number such as -200 shows the stake needed to win 100: stake 200 to win 100.
Negative numbers belong to favourites and positive numbers to underdogs. Because the two sides work differently, mixing them up is the most common beginner mistake.
Converting between formats
All three formats carry the same information, so conversion is mechanical.
- Fractional to decimal: divide, then add 1. For 5/2, 5 / 2 = 2.5, plus 1 gives 3.50.
- Positive American to decimal: divide by 100, then add 1. +150 becomes 2.50.
- Negative American to decimal: divide 100 by the number (ignoring the minus), then add 1. -200 becomes 1.50.
Our odds converter handles every format and also shows the implied probability.
From odds to implied probability
Decimal odds convert to a probability with one division: implied probability = 1 / decimal odds. A price of 2.00 implies 50%, 4.00 implies 25%, and 1.25 implies 80%. This is the bridge between "what does it pay" and "how likely is it", and it is the single most useful idea in the whole subject. We cover it in detail in our article on implied probability.
The bookmaker's margin
If you add up the implied probabilities of every outcome in a market, the total is above 100%. For a coin-flip match priced 1.90 on both sides, each side implies about 52.6%, so the market sums to roughly 105.3%. The extra 5.3 points are the bookmaker's margin, sometimes called the overround or the vig. It is how the bookmaker earns a living.
A lower margin means better value for the bettor. Comparing prices for the same outcome across providers is a straightforward way to see where the margin is smaller.
Common mistakes
- Treating a short price as a guarantee. A price of 1.20 still loses roughly one time in six or seven.
- Comparing prices in different formats without converting them first.
- Forgetting that the decimal return includes the stake, which makes profit look larger than it is.
Key takeaways
Odds describe payout and probability together. Decimal is the simplest format to calculate with, fractional and American are just different notations, and the implied probability is what lets you compare prices on equal terms. Nothing about reading odds helps you predict results, and no price guarantees a win.
Betting is for adults only (18+). Only stake money you can afford to lose, set limits before you start, and stop if it stops being fun. If gambling is causing you problems, contact a local support organisation.