Betting Odds Explained: Fractional, Decimal and American Odds

Betting odds are a compact way of stating two things at once: the chance a bookmaker assigns to an outcome, and how much a winning bet pays. They appear in three formats, fractional (5/1), decimal (6.00) and American moneyline (+500), and all three describe the same price. This guide shows how to read each format, convert between them, turn odds into an implied probability, and spot the margin that keeps a bookmaker profitable.

Odds describe a market’s view of likelihood, not a promise. Whatever the format, a favourite carries lower odds and a smaller payout, while an underdog carries higher odds and a bigger payout.

What betting odds mean

An odd is a way of writing a price for an event. It carries two pieces of information at once: how likely the bookmaker thinks an outcome is, and how much a winning stake pays back.

Three numbers matter whenever you place a bet. Your stake is the amount you risk. Your profit is the amount you win on top of the stake. Your return is the two added together, the stake plus the profit.

Every format expresses the same relationship between those three numbers. A short price such as 1/4, 1.25 or -400 points to a heavy favourite and a small profit per unit staked. A long price such as 5/1, 6.00 or +500 points to an underdog and a larger profit per unit staked. Long odds pay more because the bookmaker judges the outcome less likely.

Imagine a two-outcome market, a home win or an away win. The stronger side might be priced at 1.60 and the weaker side at 2.40. A 1.00 stake on the favourite returns 1.60 if it wins, and a 1.00 stake on the underdog returns 2.40, because the bookmaker thinks the underdog is less likely to win.

The three odds formats

Fractional, decimal and American odds are three ways to write the same price. The table below shows one identical bet, 5/1, expressed in each format.

The three right-hand columns are the same no matter which format you read. The odds do not change the event, only the notation.

Fractional odds

Fractional odds are the traditional format in the UK and Ireland, and they appear on racing and betting markets around the world. They are written as a fraction such as 5/1 and read “five to one”. The left number is the profit you receive for every unit of the right number that you stake.

At 5/1 a winning 1.00 stake pays 5.00 profit, plus your 1.00 stake back, for a 6.00 total. At 1/1, called evens, you win the same amount you stake, so a 1.00 stake returns 2.00. When the left number is smaller than the right, the bet is odds-on: at 1/4 you stake 4.00 to win 1.00 profit.

The maths is two steps. Profit equals the stake multiplied by the fraction, and return equals the stake multiplied by the fraction plus one.

Profit = stake × (X / Y)

Return = stake × (1 + X / Y)

Example: a 10.00 stake at 5/1 pays 50.00 profit and returns 60.00 in total.

Odds-on and odds-against

Fractional odds describe an outcome as either odds-against or odds-on. When the left number is bigger than the right, as in 5/1, the bet is odds-against: you stand to win more than you stake. When the left number is smaller, as in 1/4, the bet is odds-on: you must stake more than you stand to win, because the outcome is judged likely.

Evens, written 1/1, sits exactly between the two. A winning evens bet pays back double the stake, with no price edge either way.

The same idea appears in decimal and American odds. A decimal price above 2.00 is odds-against, a decimal price below 2.00 is odds-on, and 2.00 is evens. A positive moneyline is odds-against, and a negative moneyline is odds-on.

Decimal odds

Decimal odds are the continental European standard, and they are the format you will most often see first on international and crypto betting sites. The number is the total a winning 1.00 stake returns, stake included.

At 2.50, a 1.00 stake returns 2.50 total: 1.50 profit plus your 1.00 stake. At 6.00, a 1.00 stake returns 6.00. At 2.00, evens, a 1.00 stake doubles to 2.00. Decimal prices are never below 1.00, because 1.00 means a return equal to the stake and no profit.

Decimal odds are the simplest to work with, because the whole calculation is one multiplication.

Return = stake × decimal odds

Profit = stake × (decimal odds – 1)

A decimal price is always one more than the fractional version. Fractional 5/1 is decimal 6.00, evens 1/1 is decimal 2.00, and 1/4 is decimal 1.25.

American moneyline odds

American odds, also called moneyline odds, are the dominant format in the United States. They are written as a positive or negative number measured against a 100 stake.

A positive number such as +250 is the profit on a 100 stake: a 100 bet wins 250 profit and returns 350 total. A negative number such as -125 is the amount you must stake to win 100 profit: a 125 bet wins 100 and returns 225 total.

The sign marks the favourite and the underdog. Negative odds mark the favourite, which returns a smaller profit for the same stake, and positive odds mark the underdog.

Moneyline odds often sit alongside a point spread, where the favourite gives up points and the underdog receives the same start. A moneyline bet ignores the spread and simply backs one side to win, with the price set by how strongly the market favours that side.

Two rules convert moneyline prices to decimal. For positive odds, divide by 100 and add 1. For negative odds, divide 100 by the number, ignoring the sign, and add 1.

Positive: decimal = (odds / 100) + 1. For +250, that is (250 / 100) + 1 = 3.50.

Negative: decimal = (100 / odds) + 1. For -125, that is (100 / 125) + 1 = 1.80.

How to convert between formats

You rarely need to convert by hand, because most platforms let you switch the display in the settings, and the same steps appear in operator guides such as William Hill’s. The rules are still short and worth knowing.

Fractional to decimal: divide the fraction and add 1. So 5/1 becomes 6.00 and 1/4 becomes 1.25.

Decimal to fractional: subtract 1 and write the result as a fraction. So 6.00 becomes 5/1 and 3.50 becomes 5/2. Some decimal prices do not land on a clean fraction, so you round to the nearest sensible one, such as 1.67 becoming 2/3.

Decimal to American: at 2.00 or higher, subtract 1 and multiply by 100 to get a positive number, so 6.00 becomes +500. Below 2.00, divide 100 by the price minus 1 and make it negative, so 1.25 becomes -400.

American to decimal: for positive odds, divide by 100 and add 1, so +400 becomes 5.00. For negative odds, divide 100 by the number and add 1, so -400 becomes 1.25.

Fractional to American: at 1/1 or higher, multiply the fraction by 100 and make it positive, so 5/1 becomes +500. Below 1/1, divide 100 by the fraction and make it negative, so 1/4 becomes -400.

Here is a quick reference for the prices that come up most often.

Odds and implied probability

Every price can be turned into a percentage that shows how likely the bookmaker thinks an outcome is. That percentage is the implied probability.

For decimal odds, divide 1 by the price. A price of 2.00 implies 50%, 3.00 implies 33.3%, and 6.00 implies 16.7%.

For fractional odds, divide the right number by the two numbers added together. At 5/1 that is 1 / (5 + 1) = 16.7%.

For American odds, positive and negative prices use different sums. At +500 the implied probability is 100 / (500 + 100) = 16.7%. At -400 it is 400 / (400 + 100) = 80%.

Implied probability is the bookmaker’s estimate with a margin already built in. It is not the true chance of the event, and it never guarantees an outcome.

How bookmakers set and move odds

A bookmaker prices a market by first estimating the true chance of each outcome, then shortening every price to build in a profit margin. The result is a book whose implied probabilities add up to more than 100%.

After the market opens, prices move. When money arrives on one side, the bookmaker shortens that price and lengthens the other, to encourage bets on the side with less money. The aim is a balanced book, where the bookmaker holds roughly equal payouts on every outcome and keeps its margin no matter what happens. A line move therefore reflects betting flow and news as much as a change in the true probability.

This is why a price you saw at 2.10 in the morning can be 1.95 by kick-off. The event has not changed; the weight of money behind each side has.

The bookmaker’s margin

Bookmakers do not price outcomes at their true probability. They shorten every price slightly so the implied probabilities of all outcomes add up to more than 100%. The amount over 100% is the overround, usually called the margin.

Here is a worked example. A two-way market, an over or under total, is priced at 1.90 on both sides. Each side implies 1 / 1.90 = 52.63%. The two sides add up to 105.26%, so the overround is 5.26 percentage points. Turned into the bookmaker’s profit rate, the vig, that is roughly 5.0% of total stakes, because 5.26 / 105.26 = 5.0%.

To see a market without its margin, divide each side’s implied probability by the total. In the example, 52.63% divided by 105.26% is 50.0% on each side, which is the market’s true estimate of a coin flip once the margin is stripped out.

The margin is the built-in edge that means the house wins over time, and no betting strategy removes it. Odds are always probability-based and never a promise, so treat betting as paid entertainment with a built-in cost. If it stops being fun, set deposit and time limits, and get support at gamblersanonymous.org or gamblingtherapy.org.

Regulated markets try to keep that cost fair and transparent. In the United Kingdom, the Gambling Commission sets remote gambling and software technical standards under sections 89 and 97 of the Gambling Act 2005, which govern how licensed operators must run their games. The margin itself is a normal part of how a licensed bookmaker prices a market, and checking it before you bet shows you the real cost.

Common mistakes when reading odds

The most frequent error is treating fractional odds as a total return. At 5/1 the total return on a 1.00 stake is 6.00, not 5.00, because the stake comes back too. Decimal odds do not have this problem, since the number already includes the stake.

Another common slip is mixing up the American sign. A positive number such as +300 is the profit on a 100 stake, while a negative number such as -300 is the stake needed to win 100. The negative side always points to the favourite.

Finally, readers sometimes take implied probability for the true chance of an outcome. It is the bookmaker’s price with a margin built in, and a 1.90 two-way market does not mean each side is 50% likely; it means each side is priced at 52.63% so the book can show a profit.

Betting odds in crypto

The maths does not change when you bet with cryptocurrency. You fund an account with Bitcoin or another coin, your balance and bets are shown in that coin, and the same three formats apply.

A decimal price is the simplest to use, because you multiply your stake by the price. Example, using illustrative amounts: you stake 0.001 BTC at 2.50. A win returns 0.001 × 2.50 = 0.0025 BTC, which is 0.0015 BTC of profit on top of your 0.001 BTC stake. A loss forfeits the 0.001 BTC.

Fractional odds work the same way in coin. Example, using illustrative amounts: you stake 0.002 BTC at 5/1, which is 6.00 in decimal. A win pays 0.002 × 5 = 0.010 BTC profit and returns 0.012 BTC in total.

Bitcoin divides into 100,000,000 satoshis, the smallest unit recorded on the blockchain, and the milli-bitcoin (mBTC) is 0.001 BTC. Those units help when prices are quoted in whole coins: a 0.0015 BTC profit is 150,000 satoshis, or 1.5 mBTC.

The same arithmetic holds in milli-bitcoins. Example, using illustrative amounts: a 0.002 BTC stake is 2 mBTC. At decimal 2.50 it returns 5 mBTC, or 0.005 BTC, a 0.003 BTC profit. Winnings settle in the coin you staked, so you receive the coin amount back, not a fiat figure.

Whatever coin you use, the format is cosmetic. Decimal odds are the continental European standard, so they are the price you will often see first on an international or crypto betting site, and most platforms let you switch to fractional or American in the settings. The margin you learned to spot above is built into those prices in exactly the same way.

If you want to see how odds apply to specific games, our guides to baccarat odds, blackjack odds and the roulette house edge work through the numbers. For crypto betting specifically, read our page on Bitcoin sports betting, see how games prove fairness with provably fair games, and browse Bitcoin casinos. More background sits in our betting and casino guides, and our responsible gambling page covers limits and support.

Quick recap

• Fractional odds (5/1) show profit per unit staked; add the stake back for the total return.
• Decimal odds (6.00) show the total return per unit staked, stake included.
• American odds (+500 or -200) are measured against a 100 stake, and the negative side marks the favourite.
• Implied probability is 1 divided by decimal odds, and a bookmaker’s quoted market usually sums above 100%.
• The gap above 100% is the margin, the built-in edge no strategy removes.

FAQ

What do betting odds mean?

Odds state a bookmaker’s view of how likely an outcome is, and how much a winning bet pays. They come in three formats, fractional, decimal and American, which describe the same price in different notation.

How do you read fractional, decimal and American odds?

Fractional odds such as 5/1 pay 5.00 profit for each 1.00 staked. Decimal odds such as 6.00 return 6.00 total per 1.00 staked, including the stake. American odds such as +500 show the profit on a 100 stake, while -200 shows the stake needed to win 100.

What does +200 mean in betting?

A positive American price such as +200 is the profit on a 100 stake. A 100 bet at +200 wins 200 profit and returns 300 total, equivalent to decimal 3.00 and fractional 2/1.

What does -150 mean in betting?

A negative American price such as -150 is the stake needed to win 100 profit. You must stake 150 to win 100, returning 250 total, equivalent to decimal 1.67 and fractional 2/3.

How do I convert decimal odds to American odds?

If the decimal price is 2.00 or higher, subtract 1 and multiply by 100 to get a positive number, so 3.50 becomes +250. If it is below 2.00, divide 100 by the price minus 1 and add a minus sign, so 1.25 becomes -400.

What is the bookmaker’s margin or overround?

A bookmaker’s margin is the amount by which the implied probabilities of all outcomes add up past 100%. A two-way market at 1.90 and 1.90 sums to 105.26%, a 5.26 percentage-point overround that is the bookmaker’s built-in edge.