Fractional to decimal, decimal to American, and the implied probability behind any price. Type it however you have it — 5/2, 3.50, or evens.
Implied probability is what the price says the chance is — but every bookmaker price carries a margin, so the three implied probabilities in a football match add up to more than 100%. The overround is the difference.
Fractional to decimal: divide, then add one. 5/2 → 2.5 + 1 = 3.50.
Decimal to implied probability: 1 ÷ decimal. 4.00 → 25%.
Decimal to American: above 2.00 it is (decimal − 1) × 100 as a positive number; below 2.00 it is −100 ÷ (decimal − 1).
| Fractional | Decimal | American | Implied |
|---|---|---|---|
| 1/5 | 1.20 | −500 | 83.3% |
| 1/2 | 1.50 | −200 | 66.7% |
| 4/5 | 1.80 | −125 | 55.6% |
| Evens | 2.00 | +100 | 50.0% |
| 6/4 | 2.50 | +150 | 40.0% |
| 2/1 | 3.00 | +200 | 33.3% |
| 5/2 | 3.50 | +250 | 28.6% |
| 4/1 | 5.00 | +400 | 20.0% |
| 10/1 | 11.00 | +1000 | 9.1% |
| 33/1 | 34.00 | +3300 | 2.9% |
Convert all three prices in a football match and the implied probabilities will total something like 105%. That extra 5% is the overround — the bookmaker’s margin, and the reason the house does not need you to be wrong to make money.
Comparing the overround between bookmakers is the quickest way to see who is pricing a match tightly and who is not. The lower the total, the better the prices.
Acca calculator — accumulator returns, including void legs.
Lucky 15 calculator — system bets and what they really cost.
Matched betting calculator — lay stake and liability.
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