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.
Punters pricing each-way bets will find the each-way calculator handles the conversion of fractional odds to place terms automatically.
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.
Worked example
Take 11/4, a familiar-looking price for a well-backed horse in a competitive handicap. Enter it in the fractional field and three things happen immediately. The decimal equivalent reads 3.75 — the total return on a £1 winning stake, stake plus winnings. The American odds read +275 — the profit on a $100 winning stake. The implied probability reads 26.67% — the break-even chance the horse needs of winning for the bet to be a zero-expected-value proposition at those odds. All four representations describe exactly the same price; which one you prefer is a matter of convention and comfort.
Common mistakes
The commonest error is to confuse fractional odds with decimal odds of the same numbers. A horse at "2" is 2.00 in decimal terms (Evens, a fair coin) but 2/1 in fractional terms (33.33% chance, decimal 3.00). The second error is to forget that fractional odds quote profit only — so a £10 stake at 3/1 returns £40, not £30. Decimal odds, by contrast, are gross; 4.00 × £10 = £40 straight out, stake included. The third error is treating "implied probability" as a real probability; it is the bookmaker's price expressed as a percentage, and it always sums to more than 100% across a field because of the overround.
What to watch for
Odds-on prices (where the horse is expected to win) look odd when you first encounter them. A 1/2 shot is a 66.67% chance, decimal 1.50 — you stake £2 to win £1, for a total return of £3. American odds flip from positive to negative at Evens: -200 rather than +200. "Evens" and "1/1" mean the same thing; the converter will accept whichever you type. For very short prices (1/10, 1/20 and shorter) or very long ones (100/1 and upwards), the ragged edges of converting back and forth can introduce rounding differences of a penny or two; the decimal figure is the authoritative one.
Frequently asked questions
What's the difference between fractional and decimal odds?
Fractional odds (like 5/2) express the profit on a winning stake relative to the stake itself — 5/2 means five units of profit for every two units staked. Decimal odds (like 3.50) express the total return, stake plus profit, per unit staked. A horse at 5/2 fractional is at 3.50 decimal; both describe exactly the same price.
Why do my implied probabilities add to more than 100%?
Because bookmakers build a margin into every market. The sum of the implied probabilities across a race is called the overround, and it is the bookmaker's mathematical edge. The overround calculator adds them up for you and shows the size of the margin on any race.
What does "Evens" mean?
Evens is the same as 1/1 in fractional terms or 2.00 in decimal terms. A winning stake at Evens returns double your stake — a £10 bet at Evens pays £20 back. The implied probability is 50%.
How do American odds work?
American odds come in two forms. A positive number (e.g. +250) tells you how much profit a $100 stake would win — $250 in that case, for a total return of $350. A negative number (e.g. -150) tells you how much you must stake to win $100 — $150 staked to win $100, for a total return of $250. American odds are standard in the US but used rarely in UK racing.