updated regularly – latest review: June 2026
Betting odds tell you two things — the probability of an outcome happening, and how much you stand to win if it does. Understanding odds is the single most important skill in sports betting, and this guide explains everything UK players need to know before placing their first bet.
Key Facts
- Betting odds represent both the probability of an outcome and your potential winnings
- UK bookmakers display odds in fractional format (5/1) or decimal format (6.0) — both mean the same thing
- The lower the odds, the more likely the outcome — the higher the odds, the less likely but the bigger the potential return
- Every set of odds includes a built-in bookmaker margin — meaning the true probability is always slightly better than the odds suggest
- Casino Compare covers all major UK bookmakers — browse easy sports offers and medium sports offers for current free bet deals
What do betting odds mean?
Odds represent the bookmaker’s assessment of how likely an outcome is to happen. They also determine your payout if that outcome occurs. In simple terms — shorter odds mean a more likely outcome with a smaller return, while longer odds mean a less likely outcome with a bigger potential return.
For example, if a bookmaker offers odds of 1/1 (evens) on a coin toss, they are saying the outcome is a 50/50 proposition. If they offer 1/4 on a heavy favourite to win a football match, they are saying that team is very likely to win — but your return on a winning bet will be modest.
Fractional odds explained
Fractional odds are the traditional UK format and are still widely used by British bookmakers, particularly for horse racing. They are expressed as two numbers separated by a slash — for example 5/1, 3/2 or 1/4.
The first number tells you how much profit you receive for every unit of the second number staked.
Examples:
- 5/1 — stake £1, win £5 profit. Total returned: £6 (profit plus stake back)
- 2/1 — stake £1, win £2 profit. Total returned: £3
- 1/2 — stake £2, win £1 profit. Total returned: £3
- Evens (1/1) — stake £1, win £1 profit. Total returned: £2
The key point is that your stake always comes back with your winnings on a winning bet — fractional odds show profit only, not total return.
Decimal odds explained
Decimal odds are increasingly common on UK betting sites and are the default format on most exchanges and European bookmakers. They are simpler to calculate than fractional odds because the number shown already includes your stake in the return.
Examples:
- 6.0 — stake £1, total return £6 (equivalent to 5/1)
- 3.0 — stake £1, total return £3 (equivalent to 2/1)
- 1.5 — stake £1, total return £1.50 (equivalent to 1/2)
- 2.0 — stake £1, total return £2 (equivalent to evens)
To calculate your profit from decimal odds, simply subtract 1 from the odds and multiply by your stake. For example, odds of 4.0 on a £10 bet: (4.0 – 1) × £10 = £30 profit.
Fractional vs decimal — which is better?
Both formats show the same information — it is purely a matter of preference. However, decimal odds are generally easier to compare at a glance, particularly when comparing prices across bookmakers. Furthermore, decimal odds make it easier to calculate accumulator returns since you simply multiply all the odds together.
Most UK bookmakers let you switch between formats in your account settings. If you find fractional odds confusing, switching to decimal is a simple fix.
What are American odds?
American odds — also called moneyline odds — are less common in the UK but appear on some international betting platforms. They are expressed as either a positive or negative number.
A positive number shows how much profit a £100 stake returns — for example +500 means a £100 bet returns £500 profit (equivalent to 5/1).
A negative number shows how much you need to stake to win £100 profit — for example -200 means you must stake £200 to win £100 profit (equivalent to 1/2).
As a result, most UK bettors stick to fractional or decimal formats and convert American odds when necessary rather than working in them directly.
How do you calculate probability from odds?
Odds imply a probability — the higher the odds, the lower the implied probability of that outcome. Here is how to convert odds to probability:
From fractional odds: Divide the second number by the sum of both numbers. Example: 4/1 → 1 ÷ (4+1) = 0.20 = 20% implied probability
From decimal odds: Divide 1 by the decimal odds. Example: 5.0 → 1 ÷ 5.0 = 0.20 = 20% implied probability
However, implied probability from bookmaker odds always adds up to more than 100% across all outcomes in a market. This surplus is the bookmaker’s margin — also called the overround or vig. It ensures the bookmaker makes a profit regardless of the outcome.
What is the bookmaker margin?
Every set of odds a bookmaker offers includes a built-in margin that tilts the odds slightly in their favour. This is how bookmakers make money over the long run.
For example, in a coin toss with true 50/50 odds, a fair price would be 2.0 (evens) on both outcomes. However, a bookmaker might offer 1.91 on both — meaning if you bet on both outcomes, you stake £200 but only receive £191 back. The £9 difference is the bookmaker’s margin.
In practice, the bookmaker margin varies between markets. Major football leagues and top horse races carry smaller margins due to high competition between bookmakers. In contrast, less popular markets carry larger margins. As a result, sticking to well-traded markets gives you better value than betting on obscure events.
What does it mean to find value in betting?
Value betting means identifying odds that are higher than the true probability of the outcome suggests. If you believe a team has a 60% chance of winning but the bookmaker offers odds implying only a 50% chance, that represents value — the odds are higher than they should be given the actual probability.
Finding value consistently over time is what separates profitable sports bettors from recreational ones. However, beating bookmaker margins consistently is very difficult — bookmakers employ teams of analysts to set accurate prices. For most UK bettors, focusing on value is more about avoiding poor-value bets than finding guaranteed winners.
How do odds change?
Bookmaker odds are not fixed — they move in response to betting activity and new information. If a lot of money comes in on one outcome, bookmakers shorten the odds on that outcome and lengthen the odds on others to balance their liability.
Furthermore, team news, injuries, weather conditions and market sentiment all influence odds movements. Odds also typically shorten as an event approaches, particularly for horse racing, where late money often compresses prices significantly.
Frequently Asked Questions
What does it mean when odds are evens?
Evens (1/1 fractional, or 2.0 decimal) means the bookmaker considers the outcome equally likely to happen as not. A winning evens bet returns exactly double your stake — stake £10, receive £20 back (£10 profit plus your £10 stake returned).
What does SP mean in betting?
SP stands for Starting Price — the official odds at which a horse is trading at the off (the moment the race starts). If you take SP rather than a fixed price when placing your bet, your return is calculated at whatever the starting price turns out to be. SP can be higher or lower than the price available when you placed your bet.
What does each way mean?
Each way is a two-part bet — one bet on the selection to win, and one bet on the selection to place (finish in the top 2, 3, 4 or 5 depending on the race). Each way bets cost twice the unit stake. The place part pays at a fraction of the win odds — typically 1/4 or 1/5 depending on the race size. For more detail see our betting basics guide.
Why do odds vary between bookmakers?
Different bookmakers set their own prices independently and carry different liabilities on different outcomes. As a result, odds on the same event can vary between bookmakers — sometimes significantly. Comparing odds across multiple bookmakers before placing a bet — a practice called odds shopping or line shopping — is a simple way to improve your returns over time.
What does it mean when a bet is odds on?
Odds on means the implied probability of the outcome is greater than 50% — in other words, the outcome is considered more likely to happen than not. Odds on bets return less profit than the stake if they win. For example, odds of 1/2 on a £10 bet return £5 profit — you stake more than you win. However, the outcome is considered likely, which is why the price is short.
What is a price boost?
A price boost — also called an enhanced odds or odds boost offer — is a promotional price improvement offered by a bookmaker on a specific selection. For example, a bookmaker might boost the odds on a team to win from 2/1 to 4/1 as a promotion. Price boosts are usually capped by a maximum stake and available for a limited time. They represent genuine value when the boosted price is higher than the fair market price.
Summary
Betting odds are the foundation of everything in sports betting — they tell you how likely an outcome is and how much you stand to win. Fractional odds (5/1) and decimal odds (6.0) are the two main formats used by UK bookmakers, and both communicate the same information in slightly different ways.
Understanding odds also means understanding the bookmaker margin — the built-in advantage that ensures bookmakers profit over the long run. As a result, the best approach for casual UK bettors is to use free bet offers to get started, compare odds across bookmakers, and focus on well-traded markets where margins are thinnest.
For a broader introduction to sports betting, see our sports betting basics guide and betting basics guide. For current free bet offers from UK bookmakers, see our best free bet offers UK guide and browse all rated sports offers at casinocompare.uk.
Always read the full terms on the bookmaker’s website before placing any bet. Sports betting involves real money gambling. For support with responsible gambling, visit GambleAware.