How to Convert Odds
An odds converter applies a different calculation depending on the starting format and the result required. Fractional odds can be changed to decimal odds by dividing the numerator by the denominator and adding one. Starting with decimal odds, subtract one to recover fractional odds, or divide 100 by the decimal figure to calculate implied probability as a percentage. The steps below show each operation with exact calculations and the stated rounding where needed.
Fractional to Decimal
To convert fractional odds to decimals, use the formula decimal odds = numerator ÷ denominator + 1. The numerator is the figure above the slash; the denominator is the figure below it.
- Use the formula decimal odds = numerator ÷ denominator + 1. Divide first, then add one to the quotient.
- Identify the numerator and denominator, divide the numerator by the denominator, and keep sufficient decimal precision before adding one.
- For 5/2, divide 5 by 2 to get 2.50, then add 1; the resulting decimal odds are 3.50.
- For 7/4, divide 7 by 4 to get 1.75, then add 1; the resulting decimal odds are 2.75.
- For 1/4, divide 1 by 4 to get 0.25, then add 1; the resulting decimal odds are 1.25.
- For 10/11, divide 10 by 11 and add 1; the result is 1.909…, displayed as 1.91 to two decimal places.
The fractional-to-decimal calculation includes the returned stake, which is why one is added after division. For 10/11, rounding the repeating decimal to two places gives 1.91.
Decimal to Fractional
To convert decimal odds to fractions, subtract one to remove the returned stake, then express the remaining value as a fraction. Reduce that fraction to its simplest exact form.
- Begin with the decimal odds and subtract 1; the difference is the fractional value to convert.
- Write the difference over a power of ten that matches its decimal places, such as 10 for one place or 100 for two.
- Reduce the resulting numerator and denominator by their greatest common factor, keeping the ratio exactly equivalent.
- For 3.50, calculate 3.50 − 1 = 2.50, write 2.50 as 250/100, then reduce to the exact fraction 5/2.
- For 2.75, calculate 2.75 − 1 = 1.75, write 1.75 as 175/100, then reduce to the exact fraction 7/4.
Keeping the decimal places during the fraction step preserves the exact ratio: 250/100 and 175/100 reduce without changing their values. The simplified forms are easier to compare with fractional prices.
Decimal to Implied Probability
Calculate implied probability from decimal odds with the formula implied probability (%) = 100 ÷ decimal odds. The result is expressed as a percentage.
- Take the decimal odds as the divisor and set up 100 ÷ decimal odds; do not subtract one for this calculation.
- Divide 100 by the decimal figure, then express the quotient as a percentage using the same numerical value.
- For decimal odds of 2.50, calculate 100 ÷ 2.50; the implied probability is 40 per cent.
- For decimal odds of 1.25, calculate 100 ÷ 1.25; the implied probability is 80 per cent.
- Check the calculation by multiplying the decimal odds by the percentage written as a decimal; 2.50 × 0.40 and 1.25 × 0.80 each equal 1.
This result is the probability represented by the decimal price, not a separate prediction. Use the same formula for other decimal odds, retaining extra precision during division if the percentage does not end neatly.
Common Odds Conversion Table
A common odds conversion table lets you compare fractional odds, decimal odds and implied probability row by row. The entries below are grouped as short, middle and long odds, from 1/5 through 100/1. Each row presents three equivalent ways to express the same price, making it easier to scan for a particular fractional value or probability. The group labels describe the ranges represented in this table.
Short Odds
Short odds are represented here by fractional prices below evens: 1/5, 1/2 and 4/5. Their decimal equivalents run from 1.20 to 1.80, while the corresponding implied probabilities range from 83.3 per cent down to 55.6 per cent. The table continues with middle and long examples so that all three groups can be compared in one place.
| Fractional | Decimal | Implied probability |
|---|---|---|
| Short | ||
| 1/5 | 1.20 | 83.3 per cent |
| 1/2 | 1.50 | 66.7 per cent |
| 4/5 | 1.80 | 55.6 per cent |
| Middle | ||
| 1/1 | 2.00 | 50 per cent |
| 6/4 | 2.50 | 40 per cent |
| 2/1 | 3.00 | 33.3 per cent |
| Long | ||
| 5/1 | 6.00 | 16.7 per cent |
| 10/1 | 11.00 | 9.1 per cent |
| 20/1 | 21.00 | 4.8 per cent |
| 100/1 | 101.00 | 1.0 per cent |
Within the short group, 1/5 has the highest implied probability and 4/5 the lowest. The three columns make those equivalent values easy to compare without switching between separate lists.
Middle Odds
The middle group contains 1/1, 6/4 and 2/1. In the table, their implied probabilities are 50 per cent, 40 per cent and 33.3 per cent respectively. The range starts at evens, where the decimal price is 2.00, and extends through 2/1, shown as 3.00 in decimal format. These examples sit between the short entries below evens and the long prices above 2/1. Reading the fractional and probability columns together shows the progression across the group: as the listed fractional price increases from 1/1 to 2/1, the implied probability decreases from one-half to about one-third.
Long Odds
The long group consists of 5/1, 10/1, 20/1 and 100/1 in the table. Their implied probabilities are 16.7 per cent, 9.1 per cent, 4.8 per cent and 1.0 per cent, in that order. The examples begin above the middle group’s 2/1 entry and extend to the largest listed fractional price, 100/1. The corresponding decimal values rise from 6.00 to 101.00 as the implied probabilities fall. This sequence makes the relationship visible across several long prices: 20/1 represents 4.8 per cent, while 100/1 represents 1.0 per cent.
American (Moneyline) Odds
American odds, also called moneyline odds, use a signed number to express either the profit available or the stake required for a stated profit. A plus sign marks the amount won on a £100 stake, while a minus sign marks the amount that must be staked to win £100. The same prices can be represented as decimal or fractional odds, making the formats comparable. American odds are rare in the UK, where fractional and decimal formats are more familiar.
Positive and Negative Numbers
A positive moneyline number shows the profit from a £100 stake, with the original stake returned separately. For example, +200 means a £100 stake gives £200 profit. The equivalent price is 3.00 in decimal odds or 2/1 in fractional odds: the decimal figure represents the total return per pound staked, while the fraction states profit relative to the stake.
A negative number shows how much must be staked to make £100 profit. At -200, £200 must be staked to win £100, giving decimal odds of 1.50 and fractional odds of 1/2. The larger stake requirement is what the minus sign signals; it does not mean that the bettor loses £200 when the selection wins. In both cases, the moneyline figure describes the relationship between stake and potential profit, rather than using the stake-to-total-return format of decimal odds.
Read the sign before the number: plus identifies a quoted profit on a £100 stake, and minus identifies a quoted stake for £100 profit. That distinction explains why the numerical values cannot be compared directly with decimal prices without converting their format.
Converting to Decimal
Use a different formula according to the sign of the American price. For a positive number, decimal odds = 1 + number / 100. For a negative number, decimal odds = 1 + 100 / the absolute value of the number. The absolute value means using the number without its minus sign in the calculation.
For +200, substitute 200 into the positive formula: 1 + 200 / 100 = 3.00. This is the decimal equivalent of 2/1. For -200, first use the absolute value, 200, then apply the negative formula: 1 + 100 / 200 = 1.50, equivalent to 1/2. These calculations retain the stake in the decimal return, so the result is not simply the profit divided by the stake.
When converting a moneyline price, identify its sign before choosing the formula; using the positive formula for a negative price, or retaining the minus sign inside the denominator, changes the result. The positive calculation divides the quoted figure by 100 and adds one, whereas the negative calculation divides 100 by the figure’s absolute value and adds one.
Why Different Formats Exist
Odds formats reflect established betting habits in different regions, rather than different ways of describing the event itself. Fractional odds remain familiar in Britain and Ireland, particularly in racing, while decimal odds are widely used across several other markets and on exchanges. The main practical distinction is how the displayed price communicates a potential return: decimal odds include the stake, whereas fractional odds express profit in relation to the stake. Knowing which convention a display uses helps you read prices consistently when comparing betting options.
Fractional in Britain and Ireland
Fractional odds are a traditional format in British and Irish racing and betting. A price such as 5/1 is read as “five to one”: for every £1 staked, the potential profit is £5 if the bet wins. The original £1 stake is returned as well, making the total return £6. The fraction describes profit relative to the stake, not the full amount paid back.
This way of displaying a price is familiar to many racegoers and bettors in these markets. It appears in racing contexts where people commonly discuss a horse as being available at a fractional price, and the compact form can be read quickly on a betting display or racecard. Familiarity matters: someone used to thinking in terms of profit per unit staked can understand 5/1 without translating it into another format.
Fractional odds persist because they remain part of the customary language of betting in Britain and Ireland, especially around racing. They also make the profit component explicit: the numerator shows the potential profit and the denominator shows the stake used as its basis. When the stake changes, the same price still expresses that relationship; a £10 stake at 5/1 would mean £50 profit, with the £10 stake returned for a £60 total return. The format is therefore not simply a regional label: it presents the price in a way that reflects a long-standing local convention for describing betting returns.
Decimal in Europe and on Exchanges
Decimal odds are common in continental Europe, Australia and Canada, and they are also widely used on betting exchanges. Their defining feature is that the displayed number includes the original stake in the total return. For example, decimal odds of 2.50 mean a £1 stake would produce a £2.50 total return if the bet wins; that amount includes the £1 stake as well as the profit.
This presentation makes price comparison especially direct. If two selections are offered at 2.50 and 2.60, the higher decimal price represents the larger total return for the same stake, assuming each bet wins. A £10 stake at 2.50 returns £25 in total, while the same stake at 2.60 returns £26. The figures can be compared on sight because they use the same scale and include the stake, without first separating the profit from the amount returned.
That consistency suits betting exchanges, where users may scan several available prices for the same outcome, as well as markets where decimal notation is already familiar. It also helps when comparing offers across different events or providers: a decimal price of 3.00 has the same return meaning wherever it is displayed. Fractional prices remain common in Britain and Ireland, but decimal odds provide a straightforward shared format across many European, Australian and Canadian markets. For a quick comparison of potential returns on equal stakes, the decimal display is often easier to interpret.