It is but wouldn't you be better off adjusting the DD to take the overpayment into account and reviewing it in say 8 or 9 months?
Calculation as follows
(Normal units of electric before the cars+extra units the cars are expected to use)x unit rate (inc vat)+2x the amount you're in debit+one average months use with the cars)+ Membership feex12 =projected one year, you could add a bit to take you through summer clearing the debit as payments are lower (I suggest about one month) and that's your annual.
Summer 40% of that divided by 6 , winter 60% divided by 6.
If you get it about right it will even out at around 9 months, and you'll have a very good idea of your usage going forward.
Also you get to keep more of your money for longer.
Originally Posted by Dozer302