Payment hike does not align to Bulb estimated reading and my own readings

I am assuming I am doing this correctly for both gas and electicity (been in the property only 6 months):
Cost = (Current Reading - first reading * KWh rate) + (Standing charge * number of days)

If the above is right, then I do not understand why Bulb have asked for £41 more per month on my DD. All their estimated readings are less than my submitted readings, and I calculated my overall cost using the above on my manual readings.

anyone have an idea?

Edit: My current DD amount probably needs to go up a bit, maybe £10 to cover the shortfall to date and rest of the year, but certainly not £41

Hi @Richuk - thanks for your post!

Your suggested payment amount is based on your average annual usage figures along with the amount of debit on your account. I see its now set to £60, but I’d suggest making some top ups if your bills are ever more than this for the month to ensure your debit amount doesn’t build.

Georgie