Odds converter
Fractional, decimal, American and implied probability, all linked. Type or paste into any field; the others follow.
A short word on the four formats
British racing still runs on fractional odds because the fraction tells you the profit clearly — 5/2 means you get five back on top of every two risked. Decimal odds, favoured by the exchanges and by almost everyone else in the world, quote the full return per unit staked, so 5/2 becomes 3.50 (profit plus your stake). American odds, which no-one in this country ever warms to, indicate either the profit on 100 units at plus prices (5/2 is +250) or the stake required to win 100 at minus prices.
The final column is the one that actually matters when you are deciding whether a price is worth taking: the implied probability. A 5/2 shot has a 28.57% chance of winning according to the price alone — before any overround is stripped out. If your own assessment of the horse's chance comes in noticeably higher than that, the price is a value bet. If it comes in lower, it is not, regardless of how compelling the form figures look.
Two shortcuts worth remembering. Decimal minus one, over one, gives you fractional (2.50 → 1.50/1 → 3/2 → 6/4). And one hundred divided by decimal odds gives the implied percentage in a single step. Beyond that, the calculator will do what is needed.
How to read an implied probability honestly
The temptation with implied probability is to treat it as the horse's actual chance of winning. It is not. The price already has the bookmaker's margin baked into it, which means the true probability is always a little lower than what the fraction alone suggests. If you want the fair probability — the one stripped of the overround — you need to divide by the book percentage of the whole race. The overround calculator does this for you.
For quick in-the-head work, though, implied probability from the raw price is close enough. The exercise of comparing your own tissue figure to the market's implied figure is the single most productive habit in value betting. Do it consistently, across many races, and over time the pattern of where the edges lie in your own judgement will start to become clear.