Hi @anders - Slippage factor is used, almost as an arbitrary integer, to work as a scaling factor for calculating margin. In theory the higher the slippage factor (usually 25%, 50%, 75% or 100% - however can in theory be any percentage) the riskier the trade as it would feed into the calculations below to increase margin requirements.
The three calculations are
No Stop: Bet size x price (in points) x deposit factor (%)
Stop: (Deposit requirement for no stop x slippage factor %) + (bet size x stop distance from current level)
G Stop: The larger figure of the two calculations below:
Bet size x stop distance (in points) + limited risk premium
Bet size x price (in points) x deposit factor (%)
If you have any other questions please let me know. You can also check out our article on IG.com "What is slippage and how do you avoid it in trading?" which may be useful.