I think I can address this one although it's only a guess and I don't think it's too in depth, although I like nice rounded figures too.(I'm talking about money not body shapes...)
The level of direct debit depends on two things, your expected use over the next 12 months, and the amount of credit or debit in your account.
The former can only really be assessed accurately after 12 months have passed, for obvious reasons, but at the 6 month point, roughly speaking, if the usage level is assumed to be as it was when you started, that leaves whatever excess credit or debit is left after subtracting an average payment once it's made (annual divided by 12 is my guess).
So for example if you were paying £120 a month in winter, your annual would be £1200
You've just made a payment up front and your statement balance is now, say, £220 in credit.
Subtract one average payment of £100 (winter 120, summer £80), leaving an excess of £120 for the coming 12 months.
So if you were to leave the account in credit by 120
, but you could ask for a refund, with no refund that would give you 6 credits of £12 winter and 6 of £8 summer =£120 thus your DD would reduce by £12 in winter to £108 and £8 in summer to £72.
At the 12 month renewal if the annual had changed you'd effectively start again, only taking a refund if it was a significant amount.
I could of course be completely wrong, like I said it's only a guess...
Originally Posted by Gray4276