Rule 4 deductions are made because when a horse is withdrawn it means that every other horse has a better chance of winning. To balance this up a deduction is made to the winnings and the level of that deduction is dependent upon the horses chances that was withdrawn. This chance is determined by the odds of the horse that was withdrawn.
The level of deduction is outlined in our 'Rules' page but is also shown below:
The table shows the amount of the deductions based on the price of individual selections. These deductions are the amount of money that is taken from each £1 in winnings. If you win £10 and there is a 20p Rule 4you will receive £8 winnings.