Beginner's guide4 min read
How Betting Odds Work: Fractional, Decimal, Implied Probability and the Overround
A beginner's reference for reading a Cheltenham price — fractional and decimal odds, a conversion table, what the overround is and how to calculate it, SP, Best Odds Guaranteed, favourite notation, and what steamers and drifters are.
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Fractional odds
British racing quotes prices as fractions. The first number is the profit, the second is the stake needed to earn it:
- 5/1 ("five to one"): stake £1, profit £5, total return £6.
- 5/2: stake £2, profit £5 — or stake £1, profit £2.50, return £3.50.
- 4/6 ("four to six", odds-on): stake £6, profit £4 — or stake £1, profit 67p, return £1.67.
- Evens (EVS, 1/1): stake £1, profit £1, return £2.
When the first number is smaller than the second, the horse is odds-on: you risk more than you stand to win. Odds-on prices are read with the stake first in speech ("six to four on" means 4/6).
Decimal odds
Decimal odds show the total return per £1 staked, stake included. Convert from a fraction by dividing and adding 1:
- 5/1 → 5 ÷ 1 + 1 = 6.00
- 5/2 → 2.5 + 1 = 3.50
- 4/6 → 0.667 + 1 = 1.67
- Evens → 1 + 1 = 2.00
Decimal odds are easier to compare and to multiply for accumulators. Our odds pages show both.
Implied probability
Every price implies a probability: 1 ÷ decimal odds. It is the chance the horse would need of winning for the bet to break even in the long run.
| Fractional | Decimal | Implied probability |
|---|---|---|
| 1/5 | 1.20 | 83.3% |
| 2/5 | 1.40 | 71.4% |
| 4/6 | 1.67 | 60.0% |
| Evens | 2.00 | 50.0% |
| 6/4 | 2.50 | 40.0% |
| 2/1 | 3.00 | 33.3% |
| 11/4 | 3.75 | 26.7% |
| 3/1 | 4.00 | 25.0% |
| 4/1 | 5.00 | 20.0% |
| 11/2 | 6.50 | 15.4% |
| 8/1 | 9.00 | 11.1% |
| 10/1 | 11.00 | 9.1% |
| 16/1 | 17.00 | 5.9% |
| 25/1 | 26.00 | 3.8% |
| 33/1 | 34.00 | 2.9% |
| 50/1 | 51.00 | 2.0% |
| 66/1 | 67.00 | 1.5% |
Two 2026 Festival results as illustrations: Gaelic Warrior won the Gold Cup at 11/4 joint-favourite — an implied chance of 26.7% at SP. Martator won the Grand Annual at 66/1 — 1.5%. Neither number tells you the "true" chance; it tells you what the market was prepared to pay.
The overround: a three-runner example
Add up the implied probabilities of every runner and, in any real market, the total is more than 100%. The excess is the overround — the bookmaker's margin.
| Runner | Price | Implied probability |
|---|---|---|
| A | Evens | 50.0% |
| B | 2/1 | 33.3% |
| C | 3/1 | 25.0% |
| Total | 108.3% |
The overround here is 8.3 percentage points. In money terms: if the bookmaker took stakes in exactly those proportions, they would take £108.33 for every £100 paid out, whichever horse won. A "fair" book totals exactly 100%; a book under 100% would let a backer of every runner guarantee a profit, which is why you will not find one.
Bigger fields usually carry bigger overrounds, and the each-way place part has its own overround, which is often larger than the win part's. Comparing overrounds across bookmakers is the simplest way to see who is pricing a race most competitively.
SP, Best Odds Guaranteed and price-taking
- Starting price (SP): the official price at the off. Results are returned with the SP, which is why every winners table on this site shows it.
- Taking a price: betting at the fixed odds shown at the time. If the horse's price then shortens, you keep the bigger price; if it lengthens, you are stuck with the smaller one — unless the bet is covered by Best Odds Guaranteed (BOG), under which the bookmaker pays the bigger of your price and the SP.
- Ante-post prices are taken months in advance and carry a different risk: the stake is lost if the horse does not run, unless non-runner no bet applies.
Favourite notation
| Mark | Meaning |
|---|---|
| f or fav | The single shortest-priced horse in the race |
| jf | Joint-favourite: two horses share the shortest price (Gaelic Warrior, 11/4 jf, 2026 Gold Cup) |
| cf | Co-favourite: three or more share the shortest price |
The favourite is not a prediction of the winner — it is the market's view. In our verified 2026 Festival results, four of the 14 races with a recorded winning SP went to the favourite or joint-favourite; see the 2026 review.
Steamers and drifters
- A steamer is a horse whose price is shortening — money is coming for it and the bookmakers are cutting the price.
- A drifter is a horse whose price is lengthening — support is thin, or money is going elsewhere.
A move tells you something about where the money went, not about the result: a price can shorten because of informed support or because of a well-publicised tip, and the two look identical on a screen. Our market movers view shows the direction and size of moves; until a licensed feed is connected those moves are simulated and labelled DEMO.
Quick reference
- Fractional 5/1 = decimal 6.00 = 16.7% implied.
- Odds-on means the first number is smaller than the second.
- Implied probability = 1 ÷ decimal odds.
- Overround = sum of implied probabilities − 100%.
- SP is the official price at the off; BOG pays the bigger of your price and SP.
- f, jf, cf mark the favourite, joint-favourites and co-favourites.
18+. Betting involves risk. BeGambleAware.org.
SourcesSporting Life — betting glossary (SP, BOG) (opens in a new tab)accessed 14 September 2026Wikipedia — odds and implied probability (CC BY-SA) (opens in a new tab)accessed 14 September 2026Wikipedia — 2026 Cheltenham Gold Cup (SP example, CC BY-SA) (opens in a new tab)accessed 14 September 2026
Frequently asked questions
What does SP mean?
Starting price — the official odds at which a horse starts the race, returned at the off. Results are recorded with the SP, which is why our winners tables quote it.
What is Best Odds Guaranteed?
A bookmaker concession under which a bet taken at a fixed price is settled at the bigger of that price and the starting price. If you take 8/1 and the horse goes off at 12/1, you are paid at 12/1. Terms and eligible markets vary by bookmaker.
How do I convert fractional odds to decimal?
Divide the first number by the second and add 1. 5/2 is 2.5 plus 1, so 3.50. 4/6 is 0.667 plus 1, so 1.67. Decimal odds show the total return per unit staked, including the stake.
What is an overround?
The amount by which the implied probabilities of all runners in a market add up to more than 100%. If three runners are priced at evens, 2/1 and 3/1 their implied chances are 50%, 33.3% and 25%, a total of 108.3%; the overround is 8.3 percentage points and is the bookmaker's built-in margin.
What does jf mean next to a price?
Joint-favourite: two horses share the shortest price in the race. When three or more share it the notation is cf, co-favourite. A single favourite is marked f or fav. Gaelic Warrior won the 2026 Gold Cup at 11/4 jf.
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