Sports Betting Odds Explained
Placing a bet at an online bookmaker can look daunting when you are new to sports gambling. Every bet carries odds, and those odds tell you two things at once: what the bookmaker thinks the probability of that outcome is, and how much your stake will return if the bet wins. This guide walks through fractional, decimal, and American odds, with real examples and the maths worked out so you can read a betting slip with confidence.
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By the end you will be able to spot the favourite in a match, work out the implied probability of any price, and calculate what your stake returns before you tap “place bet”. We also cover Evens, Odds-On, and how the bookmaker’s overround affects the prices on offer.
A real example: Liverpool vs. Everton
Before we break down the maths, here is a set of odds taken from a real Merseyside derby.
Liverpool are the favourite. You can tell because the number on the left (17) is smaller than the number on the right (20), meaning they return less than your stake if they win. Draw at 29/10 and Everton at 10/3 are both priced above Evens, so they return more than your stake. The shorter the price, the more the bookmaker thinks it will happen.
How to Calculate Probability From Fractional Odds
Fractional odds can be converted into an implied probability using a simple formula. For odds written as X/Y, the probability is Y divided by (X + Y), expressed as a percentage.
- 1/6: 6 ÷ (1 + 6) = 85.7% chance
- 1/1 (Evens): 1 ÷ (1 + 1) = 50% chance
- 6/1: 1 ÷ (6 + 1) = 14.3% chance
Applying the same formula to the Liverpool vs Everton example:
- Liverpool 17/20: 20 / (17 + 20) = 54.1% implied chance
- Draw 29/10: 10 / (29 + 10) = 25.6% implied chance
- Everton 10/3: 3 / (10 + 3) = 23.1% implied chance
Notice those three percentages add up to 102.8%, not 100%. That 2.8% is the bookmaker’s overround, sometimes called the vig or margin. It is how bookmakers make money over time, and we cover it in more detail below.
Try Our Betting Odds Calculator
If you would rather skip the mental arithmetic, our betting odds calculator converts any fractional odds into decimal, American, implied probability, and potential returns for a given stake. Enter the two numbers and it does the rest.
How to Calculate Your Winnings From Fractional Odds
Remember that when a winning bet settles, you get your original stake back on top of your profit. There are two ways the number is usually quoted: profit only, or total return including stake. We will show both.
Profit per £1 staked is simply the first number divided by the second (X ÷ Y).
- 1/6: £1 stake returns 17p profit, £1.17 total
- 1/1 (Evens): £1 stake returns £1 profit, £2 total
- 6/1: £1 stake returns £6 profit, £7 total
Using the Liverpool vs Everton derby:
- Liverpool win 17/20: £1 stake returns 85p profit, £1.85 total
- Draw 29/10: £1 stake returns £2.90 profit, £3.90 total
- Everton win 10/3: £1 stake returns £3.33 profit, £4.33 total
So 17 ÷ 20 = 0.85, which tells you 85p profit for every £1 staked. The same method works for any fractional price, whether it is 2/5, 11/10, or 100/1.
Evens, Odds-On and Odds-Against
You will often hear odds described by name rather than by number, especially on TV coverage and inside the shop.
- Evens (sometimes written 1/1 or EVS): you win the same amount as your stake. A £10 bet at Evens wins £10 profit and returns £20 in total. Implied probability is exactly 50%.
- Odds-On: anything shorter than Evens, where the profit is less than your stake. 1/2, 2/5, and 4/9 are all odds-on prices. These are short-priced favourites that the bookmaker expects to win.
- Odds-Against: anything longer than Evens. 2/1, 5/1, 10/1 are all odds-against prices. Your profit is larger than your stake, but the outcome is less likely.
A useful shortcut when scanning a betting slip: if the left number is smaller than the right, the price is odds-on. If they are equal, Evens. If the left is bigger, odds-against.
Decimal Odds Explained
Some betting sites display prices in decimal format instead of fractions. Decimals are easier to work with because the number already includes your stake. Multiply the decimal price by your stake and you get the total return, no mental arithmetic needed.
- 6.0 × £1 stake = £6 total return (£5 profit, £1 stake)
- 3.15 × £1 stake = £3.15 total return (£2.15 profit, £1 stake)
- 1.15 × £1 stake = £1.15 total return (15p profit, £1 stake)
To find the implied probability from decimal odds, divide 1 by the decimal price. A price of 2.00 (Evens) gives 1 / 2.00 = 50%. A price of 4.00 gives 1 / 4.00 = 25%. Simpler than the fractional formula once you get used to it.
Most UK bookmakers let you switch between fractional and decimal in your account settings. If you bet on European matches or use an exchange like Betfair, decimal is usually the default.
Fractional and Decimal Conversion Table
Some common prices side by side:
- 1/5 (Odds-On) = 1.20 decimal = 83.3% probability
- 1/2 (Odds-On) = 1.50 decimal = 66.7% probability
- 4/5 (Odds-On) = 1.80 decimal = 55.6% probability
- 1/1 (Evens) = 2.00 decimal = 50% probability
- 6/5 = 2.20 decimal = 45.5% probability
- 2/1 = 3.00 decimal = 33.3% probability
- 5/2 = 3.50 decimal = 28.6% probability
- 3/1 = 4.00 decimal = 25% probability
- 5/1 = 6.00 decimal = 16.7% probability
- 10/1 = 11.00 decimal = 9.1% probability
- 20/1 = 21.00 decimal = 4.8% probability
- 50/1 = 51.00 decimal = 2% probability
- 100/1 = 101.00 decimal = 1% probability
You can derive any decimal from a fractional price by calculating (X ÷ Y) + 1. So 7/2 becomes (7 ÷ 2) + 1 = 4.50. Going the other way: decimal minus 1 gives you X/Y, so 3.50 – 1 = 2.50, which is 5/2.
American (Moneyline) Odds Briefly
If you follow NFL, NBA, or MLB betting, you will see a third format: American odds, also called moneyline. They come in two flavours.
- Positive odds (+150, +300, +500): the number shows the profit on a £100 stake. +300 means a £100 bet wins £300 profit. These are the equivalent of fractional odds-against.
- Negative odds (-120, -200, -500): the number shows how much you need to stake to win £100 profit. -200 means a £200 bet wins £100 profit. These are the equivalent of fractional odds-on.
Quick conversion: +100 American = 1/1 fractional = 2.00 decimal = Evens. Anything positive is odds-against; anything negative is odds-on. UK bookmakers rarely use American odds by default, but most offshore and global sportsbooks offer it as a display option.
Implied Probability vs True Probability
Every price a bookmaker offers has an implied probability baked into it. But those implied probabilities across all outcomes in a single event always add up to more than 100%. That difference is the overround, and it is how sportsbooks turn a profit over thousands of bets.
In the Liverpool vs Everton example earlier the three outcomes summed to 102.8%. That 2.8% margin is the bookmaker’s edge on that match. On a 1-horse-race style favourite market you might see 105%+. On a Champions League final with two evenly matched teams you might see 102% or even 101%.
What this means practically: if you want to beat the bookmaker long-term, you need to find prices where you believe the true probability is higher than the implied probability. A Premier League match where you rate the home team as a 55% chance to win, but the bookmaker is pricing them at 2/1 (implied 33.3%), is a value bet. Most punters do not do this calculation. It is also the reason seasoned bettors shop around for the best price on any given market, because even a small edge on one side of the line can tip a losing position into a break-even or profitable one.
How Odds Move Before Kick-Off
Opening prices are a starting point. Between market open and kick-off, odds move in response to team news, weather, public money, and professional bettors taking positions. A price that opens at 11/8 on a Friday might drift to 6/4 by Saturday lunchtime if team news is unfavourable, or shorten to 5/4 if the backing is heavy.
Best Odds Guaranteed (BOG) on horse racing protects you from favourable moves: if you bet at 5/1 and the horse is sent off at 7/1, you are paid at the bigger price. BOG is rare on football and other sports, but price boosts on selected matches serve a similar function by bumping specific markets above the standard price. If you are the type to bet early, BOG-style protections are worth factoring into which bookmaker you use for which sport.
How to Switch Odds Format at Your Bookmaker
Every major UK betting site lets you choose between fractional and decimal, usually under Account Settings or Preferences. A few also offer American as a third option. There is no right answer: fractional is the traditional UK way, decimal is quicker for mental calculation and standard on exchanges, and American is useful if you bet on US sports.
If you plan to shop for the best price across two or three bookmakers regularly, picking one format and sticking with it across every site makes comparison much faster. Decimal wins that contest for most people because you can compare prices at a glance without converting in your head.
Summary
Fractional odds (17/20, 5/1, 100/1) tell you the profit relative to your stake. Decimal odds (1.85, 6.00, 101.00) include your stake in the number, so multiplying by the stake gives the total return. American odds (+150, -200) are a different display convention mainly used for US sports.
Any of the three can be converted to an implied probability, which tells you how likely the bookmaker thinks the outcome is. The implied probabilities in any given market add up to slightly more than 100% because of the bookmaker’s overround. If you believe the true probability of an outcome is higher than the implied price, that is the definition of a value bet.
When you are ready to put the theory into practice, compare the best football betting sites, check our horse racing guide, or run any price through the betting odds calculator.
