Decimal, fractional, American odds: the three main formats
Published on 29 July 2026
The same probability can be written three main ways depending on the bookmaker's country. Nothing changes underneath — neither the payout nor the margin — but the reading changes completely.
The three notations
Decimal (continental Europe): the odd states the total return per unit staked, stake included. At 2.50, a €10 stake returns €25 in total, i.e. €15 of net profit. It is the easiest format to compute with.
Fractional (United Kingdom, Ireland): the fraction states the net profit relative to the stake. "6/4" means 6 units of profit for 4 staked — a €4 stake returns €6 of net profit, plus the stake. In decimal: 6÷4 + 1 = 2.50.
American (United States): a signed number pivoting around a 100 stake. "+150": a 100 stake yields 150 of net profit (decimal 2.50). "−200": you must stake 200 to win 100 of net profit (decimal 1.50). The sign flips either side of decimal odds 2.00, which equals "+100".
Other notations exist beyond these three standards — we will not cover prediction platforms here, whose "shares" trade at a price that corresponds directly to the implied probability.
Conversion table
| Decimal | Fractional | American | Implied probability |
|---|---|---|---|
| 1.20 | 1/5 | −500 | 83.3% |
| 1.50 | 1/2 | −200 | 66.7% |
| 2.00 | 1/1 (evens) | +100 | 50.0% |
| 2.50 | 6/4 | +150 | 40.0% |
| 3.00 | 2/1 | +200 | 33.3% |
| 5.00 | 4/1 | +400 | 20.0% |
The conversion formulas
Fractional to decimal: numerator ÷ denominator + 1. Positive American to decimal: odd ÷ 100 + 1. Negative American to decimal: 100 ÷ |odd| + 1. And in every case, the implied probability is read from the decimal form: 1 ÷ decimal odd.
The traps
Rounding: British fractions use a limited repertoire of traditional values; a round-trip conversion can slightly shift the result if you convert from the displayed value rather than the original one. The American sign: around 2.00, a simple sign flip (+105 / −105) corresponds to probabilities that are close but not equal — beware of quick readings. Cross-format comparison: comparing a fractional odd at a British operator with a decimal one at a French operator requires bringing everything to the same format first.
One useful reminder: the format has no effect on the RTP — the margin hides just as well in a fraction as in a decimal. The online calculator accepts all three formats, even mixed within a single analysis, and converts them instantly with no rounding drift.