WhichBookmakerCalculator · 2026-10-23
Odds converter
Type a price into any box — decimal, fractional, American or implied probability — and the other three update as you type. Below it, enter the prices for every outcome in a market to see how much margin the bookmaker has built in, and what the fair odds would be without it.
18+.
Book margin calculator
Every price includes the bookmaker's fee. Enter all the outcomes of one market — home, draw, away — and the calculator adds up their implied probabilities. The amount over 100% is the margin.
Any format: 2.10, 11/10, +110. Leave the third box empty for a two-way market (tennis, over/under).
Odds conversion table
The traditional fractional ladder with its decimal, American and implied probability equivalents. Probabilities are rounded to two decimal places; American odds to the nearest whole number.
| Fractional | Decimal | American | Implied probability |
|---|---|---|---|
| 1/5 | 1.20 | −500 | 83.33% |
| 1/4 | 1.25 | −400 | 80.00% |
| 2/7 | 1.29 | −350 | 77.78% |
| 3/10 | 1.30 | −333 | 76.92% |
| 1/3 | 1.33 | −300 | 75.00% |
| 4/11 | 1.36 | −275 | 73.33% |
| 2/5 | 1.40 | −250 | 71.43% |
| 4/9 | 1.44 | −225 | 69.23% |
| 1/2 | 1.50 | −200 | 66.67% |
| 8/15 | 1.53 | −188 | 65.22% |
| 4/7 | 1.57 | −175 | 63.64% |
| 8/13 | 1.62 | −163 | 61.90% |
| 4/6 | 1.67 | −150 | 60.00% |
| 8/11 | 1.73 | −138 | 57.89% |
| 4/5 | 1.80 | −125 | 55.56% |
| 5/6 | 1.83 | −120 | 54.55% |
| 10/11 | 1.91 | −110 | 52.38% |
| 1/1 (evens) | 2.00 | +100 | 50.00% |
| 21/20 | 2.05 | +105 | 48.78% |
| 11/10 | 2.10 | +110 | 47.62% |
| 6/5 | 2.20 | +120 | 45.45% |
| 5/4 | 2.25 | +125 | 44.44% |
| 11/8 | 2.38 | +138 | 42.11% |
| 6/4 | 2.50 | +150 | 40.00% |
| 13/8 | 2.63 | +163 | 38.10% |
| 7/4 | 2.75 | +175 | 36.36% |
| 15/8 | 2.88 | +188 | 34.78% |
| 2/1 | 3.00 | +200 | 33.33% |
| 9/4 | 3.25 | +225 | 30.77% |
| 5/2 | 3.50 | +250 | 28.57% |
| 11/4 | 3.75 | +275 | 26.67% |
| 3/1 | 4.00 | +300 | 25.00% |
| 10/3 | 4.33 | +333 | 23.08% |
| 7/2 | 4.50 | +350 | 22.22% |
| 4/1 | 5.00 | +400 | 20.00% |
| 9/2 | 5.50 | +450 | 18.18% |
| 5/1 | 6.00 | +500 | 16.67% |
| 11/2 | 6.50 | +550 | 15.38% |
| 6/1 | 7.00 | +600 | 14.29% |
| 7/1 | 8.00 | +700 | 12.50% |
| 8/1 | 9.00 | +800 | 11.11% |
| 9/1 | 10.00 | +900 | 10.00% |
| 10/1 | 11.00 | +1000 | 9.09% |
| 12/1 | 13.00 | +1200 | 7.69% |
| 14/1 | 15.00 | +1400 | 6.67% |
| 16/1 | 17.00 | +1600 | 5.88% |
| 20/1 | 21.00 | +2000 | 4.76% |
| 25/1 | 26.00 | +2500 | 3.85% |
| 33/1 | 34.00 | +3300 | 2.94% |
| 50/1 | 51.00 | +5000 | 1.96% |
| 100/1 | 101.00 | +10000 | 0.99% |
How odds conversion works
All three formats describe the same thing: what you get back for each unit staked. Decimal odds include the stake, so 2.50 returns £2.50 for every £1. Fractional odds show profit only, so 6/4 means £6 profit for every £4 staked; add 1 to the fraction to get decimal: 6 ÷ 4 + 1 = 2.50.
American odds work from 100. A plus number is the profit on a 100 stake, so +150 means 150 profit on 100, which is decimal 2.50. A minus number is the stake needed to win 100, so −150 means staking 150 to win 100, which is decimal 1.67. Evens is 1/1, 2.00 or +100.
Implied probability is 1 ÷ decimal odds. 2.50 implies 40%, 1.67 implies 60%. It is the chance the price says the outcome has — not the chance it actually has. If you think an outcome is more likely than its implied probability, the price is generous; if less likely, it is not.
Converting decimal back to fractional is not always exact, because bookmakers use a fixed ladder of traditional fractions. The converter shows the nearest one, and the exact fraction when they differ.
Worked example: finding the margin in a football match
A bookmaker prices a match at 2.10 home, 3.40 draw and 3.60 away. The implied probabilities are 1 ÷ 2.10 = 47.62%, 1 ÷ 3.40 = 29.41% and 1 ÷ 3.60 = 27.78%. Exactly one of the three must happen, so a fair book would add up to 100%. This one adds up to 104.81%.
The 4.81% excess is the overround. The margin — the share of every pound staked that the bookmaker keeps if it takes balanced money on all three — is 1 − (1 ÷ 1.0481) = 4.59%.
To find the fair odds, multiply each price by the total: 2.10 × 1.0481 = 2.20, 3.40 × 1.0481 = 3.56 and 3.60 × 1.0481 = 3.77. Those are the prices the bookmaker would offer with no margin. The gap between 2.10 and 2.20 is the fee you pay on a home bet, and it is why comparing prices across bookmakers matters more than any single bet.
Link to this calculator
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Related
Frequently asked questions
How do you convert fractional odds to decimal?
Divide the first number by the second and add 1. 6/4 is 6 ÷ 4 + 1 = 2.50; 11/10 is 2.10; evens (1/1) is 2.00; 4/6 is 1.67. The 1 you add is your stake coming back, which decimal odds include and fractional odds do not.
What does +150 or −110 mean in American odds?
A plus number is the profit on a 100 stake: +150 pays 150 profit on 100, decimal 2.50. A minus number is what you need to stake to make 100 profit: −110 means staking 110 to win 100, decimal 1.91. +100 and −100 both mean evens.
How do you work out implied probability from odds?
Divide 1 by the decimal odds. 2.00 implies 50%, 4.00 implies 25%, 1.25 implies 80%. For fractional odds, convert to decimal first; for American, use the converter above. Implied probability includes the bookmaker's margin, so it is slightly higher than the price would be in a fair market.
What is a good bookmaker margin?
On the main football markets — match result, both teams to score, over/under 2.5 goals — 2% to 4% is low, 5% to 7% is typical and anything above 8% is expensive. Margins are wider on less popular markets, outright winners and in-play. Enter the prices into the book margin calculator above to check any market yourself.