Fractional odds, explained from zero

A fractional price is a ratio of profit to stake, written as two numbers. 5/2 means five won for every two risked, and the stake comes back on top. Evens is 1/1. Anything where the first number is smaller than the second — 2/5, 1/4 — is a favourite, and is described as odds-on.

The format predates decimalisation and describes a physical transaction at a rail: you hand over the second number and, if you win, receive the first plus your own money back. That is why the stake is excluded — it never conceptually left, it was matched against the layer's stake.

The denominators are not standardised, which is what makes the format hard to scan. 11/8, 6/4 and 13/8 are three prices in ascending order and there is no way to see that at a glance, whereas the same three in decimal are 2.375, 2.50 and 2.625.

The problem arrives next. Comparing two fractional prices by eye is where the mistakes happen, particularly around evens. 8/11 and 4/6 look interchangeable and are not: 8/11 pays 0.727 per unit and 4/6 pays 0.667, so one is meaningfully better than the other on every bet.

What to do with it. Convert fractional prices to decimal before comparing any two of them: divide the first number by the second and add one.

Work it out. The odds converter turns any American, decimal, fractional or percentage price into the other three.