# Overround and probability calculator

## How to use the calculator

• The “Selection” column is optional and does not affect the calculation.
• Choose your preferred odds format; decimal, fractional or American.
• The odds for all possible outcomes must be included.
Book % 103.09%
Overround 3.09%
Book % 103.09%
Overround 3.09%
Selection
Probability
1
Must be a number greater than 1. Must be a fraction, for example 2/1. Must be "+" or "-" and a whole number over 100.
51.55%
2
Must be a number greater than 1. Must be a fraction, for example 2/1. Must be "+" or "-" and a whole number over 100.
51.55%
3
Must be a number greater than 1. Must be a fraction, for example 2/1. Must be "+" or "-" and a whole number over 100.

With the above calculator you can work out the book % and sportsbook’s overround for any betting market. This means you can check if a sportsbook is giving you good value odds and you can check whether arbitrage opportunities exist across different sportsbooks.

## How much overround should there be?

The below table is for 2 selection betting markets. It’s normal for the overround to rise as the number of selections rise, because some overround has to be added to the odds of each selection.

It is almost impossible to make long term profit if your sportsbook gives you odds with more than a 5% overround. See our best odds sportsbook rankings to find out if that is the case with your sportsbook.

## Overround of 50/50 odds

A 50/50 bet is one that has an equal chance of winning or losing. Totals and spreads are often 50/50 markets. If there was no overround the odds would be 2. Below is the overround for different 50/50 odds.

1. #### Tictacman

Just to emphasis a point on percentages, top 5 finish on betfair in the Scottish open was overround by, stand by, 3822% can you believe that!!!

2. #### Tictacman

You really need to understand overround markets in order to use the exchanges. This is a great tool for working out the book margins.
“know when to hold em, know when to fold em” I wouldn’t be without it.

3. #### Megan

How many sportsbooks actually have an overound of 0-3.5% on big events? Why do they increase it for smaller events???

• #### BitEdge

Sportsbooks have larger edges on less popular events because they get less bets on them so they are less profitable, and because they are more uncertain.

4. #### Anonymous

this is a great tool, thanks. i can now see which sportsbooks are trying to rip me off!

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