The goal of this page is to broaden the reader’s knowledge of sports betting — why bookmakers almost always win in the long run, and how it is possible to turn the game in your favour.
Many people think they can make money from sports betting just by sticking to leagues and sports they know well. Bookmakers are aware of this and constantly try to exploit it to their advantage.
Knowing about a sport or league doesn’t help if you don’t know how to use that information or how to avoid misusing it. Out of 1000 people who start betting, only a handful will beat bookmakers in the long run, even if many have deep knowledge of various sports.
To win long-term, you need to be able to assess the true probability of an outcome. Since bookmakers are often better at estimating these probabilities, hobby bettors frequently get poor odds and lose over time — even if they win more individual bets than they lose.
The most important concept in sports betting is expected value — the expected return on your stake over time.
If you bet without adequate data and theory, the expected value is negative, which means you’ll lose money in the long run. To make money, you need positive expected value.
In games like roulette, because the odds pay out less than true probability, the expected value is negative — and you will lose money long-term. The same logic applies to sports books: the bookmaker’s margin ensures they make money unless you find bets with positive expected value.
Imagine starting with a bankroll of £1,000 and placing 1,000 bets at odds of 1.83 on outcomes that each have a true 50% probability.
Over time, you’ll win roughly as many bets as you lose — but because of the bookmaker’s margin, your bankroll will steadily decline.
This is how bookmakers make their money. If they offered fair odds (2.00 vs 2.00 in a 50/50 match), they wouldn’t have a guaranteed edge. But even with their margin, there are still situations where the bookmaker gets it wrong.
When you bet at odds of 1.83, the bookmaker is effectively pricing each outcome as if it has about a 54.6% chance of winning, even if the true probability is only 50%. That difference is where their edge comes from. Using a simple expected value calculation, a bet like this returns –8.5% in the long run, meaning you lose money even if your win rate is perfectly average. In practical terms, that’s a loss of £8.50 for every £100 staked, or £85 for every £1,000. So even if you win just as often as you lose, you’ll still steadily go backwards — because you’re being paid less than the true odds of the outcome.
Now that we’ve covered how bookmakers profit, let’s shift focus to how you can profit.
You make money when the odds you bet are higher than the true probability of the outcome
That’s positive expected value.
For example, imagine you have a statistical model for table tennis that rates two players — Joe and Bob — as evenly matched, each with a 50% chance of winning.
If a bookmaker offers 2.20 on Bob to win, that’s a value bet.
If you stake £1,000 every time you find a similar opportunity — where a player has a 50% chance but is priced at 2.20 (10% EV) — you’ll make an average profit of £100 per bet over time.
However, it’s crucial to understand that you can’t confirm the EV of your model without a sufficient sample size. Models can be wrong. A sample size of around 500 bets is usually enough to validate your strategy.
If you place 1,000 bets at odds of 2.20 on outcomes with a true 50% probability you’ll win and lose roughly the same number of bets but because of the higher odds, you’ll generate profit over time.
That’s what positive expected value looks like in practice.
Look at the red line on the graph, for example. This shows a positive strategy that actually starts off losing money. The bets are still value bets but the value has not yet been actualised due to variance and a relatively small sample size.
These examples show just how important odds are.
People on Instagram or Twitter claiming they have “guaranteed bets” or that they know what will win are simply misleading you — usually to make money from you in some way.
There are no certainties in betting.
Every outcome has a probability attached to it.
Any team can lose
Any player can lose
The only question is: how often does this happen?
Next time someone says a price is “too high” because of injuries or news, ask yourself:
Is this information already public?
If Haaland is injured, of course it affects his team — but if everyone already knows, it’s already reflected in the odds.
Major betting markets — like the Premier League or NBA — are some of the most efficient prediction systems in the world.
The organisations and bettors moving the most money have more information and sharper models than the average person.
However, there are so many different leagues and sports on offer now and so many different markets within this that it is impossible for the bookmakers to cover everything with the same level of scrutiny. Exploiting these oversights is the crux of being a successful sports bettor.
At first glance, it might seem impossible to make money from betting.
But here’s the key insight:
In market’s with good liquidity you can learn from the market’s efficiency. In large markets, the odds at kickoff are generally the most accurate estimate of the true probability.
So if your bets consistently beat those closing odds, you’re likely profitable.
If you regularly place bets at 2.20 that later move to 2.00 before kickoff, you have an edge.
This concept is known as closing line value (CLV) — and it’s one of the strongest indicators of long-term profitability.
We focus on multiple bets (accumulators) because they allow you to combine value into a single bet. Think of each selection as having a small edge — the odds are slightly better than they should be. On their own, that edge is good, but when you combine several of these selections together, the value compounds. In simple terms, you’re multiplying one good bet by another good bet, which increases your overall advantage. While multis are naturally more volatile and won’t win as often, when they do land, they deliver a stronger return because the value has been stacked across every selection.
A bet represents the probability of a particular outcome occurring and shows how much you can win relative to your stake. Odds can be shown in different formats, the main formats are: fractional (2/1) decimal, and American.
You can also convert odds into a percentage to show the implied chance of an event happening. The implied probability is the probability that a given odd represents.
To calculate implied probability from decimal odds:
Implied probability (%) = (1 / odds) × 100
For example:
If a team has decimal odds of 2.00 to win a match, the implied probability is 50% (1 divided by 2.00, times 100). If you believe the team actually has a 60% chance, you have found value.
ROI stands for Return on Investment. It measures how profitable you are as a bettor. It’s not very meaningful until you’ve placed a larger number of bets (ideally over 100).
If your ROI is +5%, you win on average £5 for every £100 staked. Most successful sport bettors have an ROI between 5% and 15% but you can make a living off betting off as low as 2 or 3% ROI.
Two bettors might think the same bet is good, but if their bankrolls differ in size, their actual stakes will differ. That’s why the industry uses units — a universal measure of stake size relative to bankroll.
One unit typically equals 1-3% of your total bankroll. If you stake 3 units instead of 1 unit, it means you think this bet has more value. However, 1 unit can be a larger amount than 3 units for someone else with a bigger bankroll. Many tipsters share which unit system they use.
Common unit systems are 1-3 units, 1-5 units, and 1-10 units
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Bankroll management is key if you want to win long-term in betting.
It’s generally recommended to only bet 1-3% of your total betting bankroll per wager. That way you run very little risk of going bust, as long as your bets have positive expected value.
