Understanding Probability In Betting: What You Need To Know

If you’re looking to start betting on sport, then the first thing you’re going to need to understand is probability.

Not only will it help you back a winner, but it’s absolutely vital in calculating odds and understanding who a bookmaker is backing as favourites.

Here at thatsagoal we can help. In fact, this guide will explain exactly how you calculate probability from betting odds…


What Is Probability In Betting?

Probability is a relatively simple concept to understand. It’s a system that takes all the possible outcomes of an event and works out the chance of one of those outcomes occurring.

For example, a dice has six sides, all numbered. The chance of a number two being rolled on a dice is therefore one in six.

The same applies in sports betting, although probability is a little more subjective.

Let’s take football betting as an example and a Premier League fixture between Manchester City and Newcastle United.

When it comes to the Match Result market there are three possible outcomes:

Manchester City win


Newcastle United win

In theory, that would mean there’s a 33.3% chance of each event happening. Now, we all know that Manchester City would win more times than 1 in 3, and therefore bookmakers take into a whole heap of information before calculating their probabilities.

This is then calculated into odds, in which punters themselves can work out a bookmakers probability.


Calculating Probability With Fractional Odds

Calculating the probability of an outcome an online bookmaker is offering can be easily done through fractional odds.

This can be done across any sport and any market and it essentially just requires calculating the odds.

Let’s take a relatively simple set of odds such as 4/1. When it comes to fractional odds, a bookmaker is predicting that of the total number within the fraction (in this case five), the number on the right is how many times the outcome will happen, and the number on the left it won’t.

So, if you were to bet on Newcastle to beat Manchester City at 4/1, the bookmaker is essentially predicting that this would happen once in five attempts.

This is the case with any odds, whether it be betting on football, horse racing, roulette and any other betting market.

When it comes to fractional odds, you can also calculate your return from the probability offered by bookmakers.

Like probability, the numbers within the fraction hold significance. The figure on the right hand side is the amount of the bet required to win the figure on the left.

So, with odds of 4/1 you would be required to wager £1 in order to win £4, alongside your stake giving you a total return of £5.


Calculating Probability from Decimal Odds

You can also calculate the probability of an outcome from decimal odds.

Decimal odds essentially represent your return from a £1 bet, including stake. For example, if the odds were 1.33, you would make a profit of 33 pence. If the odds were 2.33, you’d get a return of £2.33.

Therefore to calculate your return you simply multiply your stake by the decimal odds.

In order to calculate probability, all you need to do is place the odds in a simple calculation:

Probability = 1 / Decimal Odds

Let’s say Paddy Power are offering odds of 1.33 on Manchester City to beat Newcastle United. If you wanted to calculate the probability, you would use the following formula:

1 / 1.33 = 0.75

That would mean that, in the eyes of the bookmaker, Manchester City have a 75% chance of winning the game.

You can select your preferences of odds with most bookmakers, so whichever formula you find easiest to calculate you’ll be able to work out the probability.


What Bookmakers Consider When Calculating Probability

Bookmakers use a wide range of information when calculating probability in their odds.

Just as our football betting tips take into account the likes of form, injuries and suspensions, and head-to-head stats, so do bookmakers’ oddsmaking.

They don’t leave any stone unturned and take everything into account from the number of shots a team regularly has on target to how a player generally performs against the opposition.

Unlike the roll of a dice, it is deeply subjective with some of the finest heads in the game calculating odds. And, let’s face it, they don’t often get it wrong do they?!


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