Any discounts that are dependent on your behaviour are not factored into your bill calculation. For example some suppliers may give you a discount for “prompt payment”, i.e. if you pay your bill shortly after receiving it. We don’t factor that in our calculation as you could pay later one month, and then your bill would be higher.
We factor all the other discounts, i.e. the ones you will receive automatically. For example some suppliers may give you a “dual fuel” discount for getting both gas and electricity from them. We factor that in our calculation because it is not dependent on your behaviour and will not change from a month to another.