By the OpenBookies team · Updated July 2026 · 7 min read
Every price on a betting shop wall — 5/1, 6/4, 11/8 — is telling you two things at once: how much you'd win, and how likely the bookmaker thinks the outcome is. Once you can read odds, everything else about betting makes sense. This guide covers fractional odds (the UK shop standard), decimal odds, implied probability, and the bookmaker's margin, with worked examples throughout.
Fractional odds
Fractional odds are the traditional UK and Irish format, and what you'll see on the printed racing pages in any betting shop. The fraction shows profit relative to stake: at 5/1 ("five to one"), you win £5 for every £1 staked, and you get your stake back too.
Worked example: £10 on a horse at 5/1. If it wins, your profit is £10 × 5 = £50, plus your £10 stake back — a total return of £60. At 6/4 ("six to four"), you win £6 for every £4 staked, so £10 returns £15 profit plus the £10 stake: £25 in total.
When the first number is smaller than the second — 1/2, 4/6, 8/11 — the selection is odds-on: it's considered more likely to win than lose, so the profit is smaller than the stake. £10 at 1/2 returns just £5 profit. "Evens" (1/1) means you double your money.
Decimal odds
Decimal odds show the total return per £1 staked, including the stake. 5/1 in fractions is 6.00 in decimals: £1 staked returns £6. The conversion is simple — divide the fraction and add 1. So 6/4 = 1.5 + 1 = 2.50, and 1/2 = 0.5 + 1 = 1.50. Anything below 2.00 is odds-on.
Decimals dominate online, on betting exchanges and across Europe because they're easier to compare and multiply (which matters for accumulators). UK shops still lean on fractions, but self-service terminals often let you switch formats, so you can use whichever reads more naturally to you — the payout is identical either way.
Odds conversion table
| Fractional | Decimal | Implied probability |
|---|---|---|
| 1/5 | 1.20 | 83.3% |
| 1/4 | 1.25 | 80.0% |
| 1/2 | 1.50 | 66.7% |
| 4/5 | 1.80 | 55.6% |
| 1/1 (evens) | 2.00 | 50.0% |
| 6/4 | 2.50 | 40.0% |
| 2/1 | 3.00 | 33.3% |
| 3/1 | 4.00 | 25.0% |
| 4/1 | 5.00 | 20.0% |
| 5/1 | 6.00 | 16.7% |
| 8/1 | 9.00 | 11.1% |
| 10/1 | 11.00 | 9.1% |
| 16/1 | 17.00 | 5.9% |
| 25/1 | 26.00 | 3.8% |
| 50/1 | 51.00 | 2.0% |
| 100/1 | 101.00 | 1.0% |
Implied probability
Odds are just probability written a different way. For fractional odds A/B, the implied probability is B ÷ (A + B). At 5/1 that's 1 ÷ 6 ≈ 16.7%; at evens it's 50%. For decimals, divide 1 by the odds: 4.00 implies 25%.
This is the single most useful idea in betting: when you back a selection, you're implicitly saying you think its real chance is better than the implied probability. If you think a team priced at 3.00 (33.3%) actually wins that match 40% of the time, that's what bettors call value — regardless of whether the bet wins on the day.
The bookmaker's margin (overround)
Add up the implied probabilities of every outcome in a market and you'll get more than 100%. A tennis match priced at 4/6 and 11/10 implies 60% + 47.6% = 107.6%. That extra 7.6% is the overround — the bookmaker's built-in margin. It's how bookmakers aim to profit whatever the result, and it's why comparing prices across bookmakers matters: the same horse can be 4/1 in one shop and 9/2 next door.
Converting odds yourself
You don't need the table for prices it doesn't list — the arithmetic is quick enough to do on your phone, or in your head with practice:
- Fractional → decimal: divide the fraction, add 1. 11/8 = 1.375 + 1 = 2.375. 4/9 = 0.444 + 1 = 1.44.
- Decimal → fractional: subtract 1, then express as a fraction. 3.50 − 1 = 2.5, which is 5/2.
- Fractional → implied probability: bottom ÷ (top + bottom). For 11/8 that's 8 ÷ 19 ≈ 42.1%.
- Decimal → implied probability: 1 ÷ decimal odds. 1 ÷ 2.375 ≈ 42.1% — same answer, as it should be.
Two prices trip almost everyone up at first. 6/4 and 4/6 sound alike but are very different bets: 6/4 (2.50) is odds-against, 4/6 (1.67) is odds-on. And "6/4 on" is shop slang for 4/6 — when a price is quoted "on", flip the fraction. If a cashier or a racing pundit says a horse is "five-to-four on", the actual price is 4/5.
How odds multiply in accumulators
Decimal odds earn their keep when you combine selections. The combined odds of a double, treble or accumulator are simply each leg's decimal odds multiplied together. Three selections at 2.00, 1.50 and 3.00 make a treble at 2.00 × 1.50 × 3.00 = 9.00 — so £10 returns £90 if all three win. Doing the same sum in fractions (evens × 1/2 × 2/1) is far more awkward, which is why even fraction-first shops settle multiples in decimals behind the scenes. For what those bets are and when to use them, see types of bets explained.
Rule 4: when winning odds get trimmed
One racing quirk worth knowing before it surprises you at the counter: if a horse is withdrawn after you've taken a price, the remaining runners' chances improve, so winning bets struck at the old prices are reduced by a standard Rule 4 deduction. The deduction is a fixed scale set by the price of the non-runner at withdrawal — anywhere from 5p in the pound for a big outsider up to 90p in the pound if the favourite comes out. Your stake is never touched, only the winnings. If your £10 at 5/1 wins but a 2/1 shooter was withdrawn (a 30p deduction), your £50 profit becomes £35. SP bets placed after the withdrawal aren't affected because the market has already been re-formed.
Starting Price vs taking a price
On horse and greyhound racing you have a choice. Take the current board price when you bet ("taking the price") and that's what you're paid at, win or lose the market move. Or let the bet settle at the Starting Price (SP) — the official odds at the off. If you back a horse at 5/1 early and it starts at 3/1, taking the early price was worth an extra £20 profit on a £10 bet. Some bookmakers offer "best odds guaranteed" on racing, paying the bigger of your taken price and the SP — check in shop whether it applies.
Reading odds in the shop
In practice: the screens and printed pages show fractional prices next to each selection. Prices shorten (get smaller) when money comes for a selection and drift (get bigger) when it's unfancied. A "steamer" is a horse whose price is collapsing; a "drifter" is the opposite. None of this movement changes a price you've already taken.
Why do prices move at all? A bookmaker's opening odds are a forecast, and the market corrects it. If far more money arrives for one runner than the price justified, the bookmaker shortens it to limit their exposure and pushes out the others to attract balancing money. News moves prices too — a key player ruled out an hour before kick-off, a going change at the racecourse, a stable's runners hitting form. By the off, the Starting Price usually reflects the sharpest collective judgement available, which is exactly why beating the SP consistently is the classic test of whether a bettor is finding genuine value.
A last bit of shop vocabulary, since the jargon can be half the battle: the favourite (marked "F" or "Fav" on screens) is the shortest-priced runner, and a joint favourite ("JF") shares that honour. An outsider is a big-priced runner, and "rag" is the affectionate term for the biggest price in the race. "Odds-against" simply means bigger than evens. You'll pick the rest up quickly — most of it is arithmetic wearing a flat cap.
New to the shop routine itself? Start with how betting shops work, then see types of bets explained for what you can actually do with these odds.