Odds Converter Guide: Fractional, Decimal, American and Implied %

To convert fractional odds to decimal, divide the top number by the bottom number and add 1, so 5/2 becomes 3.50. To convert back, subtract 1 and write the result as a fraction. Implied probability is 1 divided by the decimal price, so 3.50 implies 28.6%. The rest of this guide gives the formulas, a conversion table and worked examples, and our odds converter will do any of it for you instantly.

UK bookmakers traditionally show fractions, such as 5/2 or 4/6. Betting exchanges use decimal, many UK bookmakers let you switch to it in their settings, and American odds are standard in the US. They are three ways of writing the same price.

Fractional to decimal#

Decimal = (top ÷ bottom) + 1

The fraction shows your profit relative to your stake. At 5/2 you win £5 for every £2 staked, so £10 wins £25. Decimal odds include the stake, which is why you add 1.

Any fraction below 1/1 (such as 1/2 or 4/6) is "odds-on": you stake more than you can win, and the chance implied is above 50%. Evens is 1/1, or 2.00. Anything bigger is "odds-against".

Decimal to fractional#

Fractional = decimal − 1, written as a fraction

3.50 − 1 = 2.5, which is 5/2. 1.80 − 1 = 0.8, which is 4/5. UK bookmakers do not use any fraction they like, though. They round to a standard ladder, so the decimal you compute may not match a fraction exactly:

A slip priced in fractions can therefore return slightly different pounds from the same bet priced in decimals, once accumulators multiply the rounding.

Stake and return#

• Fractional: profit = stake × fraction. Return = profit + stake.
• Decimal: return = stake × decimal. Profit = return − stake.

A £10 stake at 5/2 makes a profit of £25 and returns £35. At 3.50, £10 × 3.50 = £35 return. Same bet.

American odds#

American (moneyline) odds use a number with a sign, based on a 100 unit.

• Positive (+): the profit on a 100 stake. +150 means 150 profit, which is 2.50 in decimal.
• Negative (−): the stake you need to win 100. −200 means staking 200 to win 100, which is 1.50 in decimal.

Formulas

• Positive: decimal = (American ÷ 100) + 1
• Negative: decimal = (100 ÷ |American|) + 1

The −110 line you see on US spreads and totals is the same as 10/11, a 52.4% implied chance on each side. We will come back to that, because it shows the bookmaker's margin.

Odds to implied probability#

Implied probability is the chance a price suggests.

• Decimal: 1 ÷ odds. So 2.50 implies 1 ÷ 2.5 = 40%.
• Fractional (a/b): b ÷ (a + b). So 6/4 implies 4 ÷ 10 = 40%.
• American positive: 100 ÷ (odds + 100). So +150 implies 100 ÷ 250 = 40%.
• American negative: |odds| ÷ (|odds| + 100). So −150 implies 150 ÷ 250 = 60%.

All four examples above are the same 40% price, from four different formats.

Worked example 1: a match result market#

A Saturday 3pm match is priced 11/10 home, 5/2 draw and 13/5 away.

The three chances add up to 104.0%, not 100%. The extra 4.0% is the bookmaker's margin, known as the overround. Divide each by 1.04 to get fair chances of 45.8%, 27.5% and 26.7%. Our guide to implied probability and removing the margin covers that step.

Worked example 2: an accumulator in fractions#

Four legs priced 4/6, 5/4, 11/10 and 2/1, and a £10 stake.

1. Convert each to decimal: 1.667, 2.25, 2.10 and 3.00.
2. Multiply: 1.667 × 2.25 × 2.10 × 3.00 = 23.63 (more precisely 23.625).
3. Return: £10 × 23.625 = £236.25. Profit: £226.25.
4. In fractions the combined price is 22.625/1, or 181/8.
5. Implied chance of the whole bet: 1 ÷ 23.625 = 4.2%.

You cannot multiply fractions directly and read off a fraction. Convert to decimal, multiply, then subtract 1 to go back. The acca calculator works out combined odds and returns, and how acca odds are calculated shows the logic.

Worked example 3: American odds and margin#

A two-way market quoted −110 on both sides. Each implies 110 ÷ 210 = 52.4%. Together they add up to 104.8%, so the overround is 4.8%. Strip it out and each side is a fair 50.0%, with fair odds of 2.00 (+100, evens). The bookmaker pays 1.91 where fair is 2.00. Over several legs, that gap compounds, as shown in the hidden cost of accumulators.

Common mistakes#

• Treating the implied chance as true. It includes margin. A 2.10 price implies 47.6%, and the fair chance may be nearer 45.8%.
• Forgetting the stake in decimal. Decimal 3.50 returns 3.5 times the stake, but the profit is 2.5 times.
• Reading −110 as a loss. The minus sign means you stake 110 to win 100. It is an odds-on price.
• Mixing formats in one calculation. Convert everything to decimal first.
• Rounding too early. Keep three decimal places until the end, especially with accumulators.

Quick mental conversions#

• Evens is 1/1 and 2.00. If the top number is smaller than the bottom, the price is odds-on and the decimal is below 2.00.
• 1/2 = 1.50, 2/1 = 3.00, 3/1 = 4.00, 4/1 = 5.00. Decimal is the fraction plus 1.
• 6/4 = 2.50 and 5/2 = 3.50, which many people mix up. 6/4 is 1.5-to-1, 5/2 is 2.5-to-1.

Using conversions to build better accas#

Once prices are in decimal, the arithmetic of an acca is simple: multiply the prices and multiply the chances. Prices in any format become a chance with one step, and that chance is the thing to compare. See how to build a football accumulator for the full process. For picks priced in the format you prefer, the generator shows odds, de-vigged probability and reasoning for each leg, and the daily picks on the acca tips page do the same.

18+ only. Converting odds does not change your chances. Accumulators lose more often than they win, and implied probabilities are estimates, not promises. Gamble only with money you can afford to lose. Free, confidential support is available from BeGambleAware.org and the National Gambling Helpline (GamCare) on 0808 8020 133. You can block yourself from UK-licensed online gambling sites with GAMSTOP.