What’s the difference between decimal and fractional odds?

Mathematically, there is no difference, whatsoever, between decimal and fractional odds and the choice between them is purely a matter of personal preference. Odds are expressions of the likelihood, or implied probability, of a particular outcome of a horse race; decimal and fractional odds are simply different ways of expressing the same market prices. Nowadays, most online bookmakers allow customers to switch back and forth between decimal and fractional odds at will.

Decimal odds, a.k.a. European odds, are expressed as decimal values, which represent the total payout, rather than the profit, for each unit stake wagered. In other words, the stake is incorporated into the odds offered; at decimal odds of 3.00, a winning £1 bet returns £3. Decimal odds are arguably the easiest way of comparing odds between bookmakers, but may appear, at least to the uninitiated, more favourable than equivalent fractional odds.

By contrast, fractional odds, a.k.a. British odds, are expressed as proper or improper fractions or, in other words, the ratio of two numbers separated by a slash, or hyphen, in the form 2/1, or 2-1. Unlike decimal odds, they do not incorporate the stake, so represent the profit on a winning bet for each unit stake wagered, rather than the total payout; at fractional odds of 2/1, a winning £1 bet returns £3, including the £1 stake, which is returned.