# How to Calculate Probability in Sports Betting

Probability is one of the key concepts in any form of gambling. Whether you are playing roulette at a high-stakes game or placing a bet on the next Premier League match, you will want to know the chances of each outcome. The chances of an event – be it a roll of the dice or a game of football – can be calculated using basic mathematics, which you can then apply using common sense. This blog post will introduce you to the various techniques used to measure probability and help you apply them in your own sport betting activities.

## Rerun and Reversal

The first method you will encounter if you are new to sports betting is, quite simply, retrying your bet. In the world of sports betting, this is known as a reverse laydown. Let’s take a look at an example:

You have made a £10 wager on Tottenham Hotspur to win at Leicester City. The match has ended in a stalemate and you are looking for an outcome that will allow you to win your bet. You decide to put another £10 on Leicester City to win at any cost. When the second match ends in a draw, you will still have your original £10 bet, but you also have an additional £20 on Leicester City. In a nutshell, you have doubled your money, but you also have to pay out £10 to the bookie for taking one step forward then two steps back. In most cases, this is a losing move, but in the right circumstances, it can be a lucrative one.

Often, you will hear people talking about backing a winner, which in this case would be Spurs. In general, you should always avoid backing a ‘winner’ when the outcome of the game is uncertain, as in this example. However, in some cases, where you think the odds are stacked against the opposition, you can make a profit from backing a ‘loser’. In other words, you will have to carefully consider whether or not backing a side that is losing, but in which you believe there is a good chance of them winning, is a good idea. After all, if they do end up losing, you will lose your original money, but you might also make a considerable profit from the winnings. This is the essence of backing a ‘loser’ – you believe they will lose, but you also think there is a good chance they will win. Calculating the probability of this happening is, however, extremely difficult, and it is usually better to play it safe by placing a safe limit on your bet. In this particular case, a profitable reverse laydown could be had by laying £30 on Tottenham Hotspur to win and backing Leicester City to draw; or lay £20 on Tottenham Hotspur to win and back a draw; or lay £10 on both sides to win at any cost.

## Layering and Exchanges

As you will have already guessed, the practice of layering is very relevant to sports betting. In layering, you are simply placing multiple bets on the same event, but at different prices. For example, if you are a long-shot enthusiast and believe that Manchester United have a one-in-four chance of winning at Chelsea, you might decide to lay £60 on United to win at Chelsea, and £30 on them to win any other game. Alternatively, you could lay £40 on United to win at any price and £20 on them to win at Chelsea. The principle behind layering is to reduce the variance of your wager – in this case, you are reducing the chances of losing. Bear in mind, however, that this could potentially multiply your winnings: if United do end up winning, you will have to pay out the full amount you were quoted, regardless of whether or not you made a profit on the other bets. In most circumstances, layering is a useful tool for betting sports, as it allows you to reduce the chances of losing, while increasing the chances of profit. It is always important to keep in mind the principle of risk and reward – by reducing your variance, you are reducing the chances of losing, but you are increasing the chances of profit. In the example above, layering United and placing a £10 wager on them would still leave you with a £10 profit, as opposed to risking £20 on a single bet.

There is another useful technique for betting that is often referred to as an exchange. With an exchange, you are simply taking one set of odds and exchanging them for another. For example, you might decide to lay £10 on Manchester United to win at any price, and also lay £10 on Chelsea to win at any price. If United do end up winning the match, you will have to pay out £20, but you will also have £20 in winnings. It is always preferable to lay the same odds on two consecutive games, or events, as exchanging one set of odds for another can sometimes lead to you losing more than you would have won had you not made the exchange. In the example above, it is preferable to keep the odds the same and not make any exchanges. If you have a preference for either team – either you think they have a better chance of winning or you want to lay more money on them – you can apply reason and make an educated guess, rather than lay multiple bets, which in many cases can be a profitable move. Calculating the chance of winning with exchanges is often very tricky, and in most circumstances, it is preferable to avoid making them altogether.

## The Law of Total Probability

When placing a bet on a sporting event, or any other form of wagering for that matter, it is imperative to keep in mind that you are ultimately placing a bet on a combination of events. In other words, the odds you are being offered are not the odds of just one event, but rather the chances of all the combined events. For example, if you are being offered 2-1 on Manchester United to win, that does not mean that their win odds are twice as high as those of the opposition. Rather, it is often the case that the odds of a draw are the same as or even lower than those of a win. In the same way, if Tottenham Hotspur are offering 2-1 odds on them to win the match, that does not mean their chances of winning are twice as great as those of Liverpool. In reality, your chances of seeing either result – whether you win or lose – are exactly the same. The key takeaway from this example is that the odds you are being offered should always be taken with a grain of salt. It is rarely the case that one event – be that a win, loss or draw – will completely determine the result of a game. Rather, in most cases, the combined outcomes of a series of events will determine the final result. For this reason, a key rule in any form of wagering is this: never put all your eggs in one basket. Always be sure to spread your bets over as many different events as possible, as this will greatly reduce the chances of any one outcome determining the outcome of the game. Knowing how probability works allows you to take a more considered approach to betting, rather than simply accepting whatever is thrown at you. This in turn will make you a better, more experienced sports bettor.