Just received my final electricity account & DD rebate from SWALEC having switched suppliers.They now bill every 6 months so they estimate reading after 3 months - normally this wouldn't matter but as there have been 4 different tariffs between 1st March and 4th September when I left it does make a difference!

Basically they have worked it so that I have used more units in 86 days since the June estimate date than I used in the 95 days from March to June, about 400 units more;what this means is that I'm paying for a greater proportion at the new (higher) rates.I estimate that this has cost me ~£5 vs an even split - they have already sent me a cheque for the DD overpayments so I think I'm on a hiding to nothing - but I'll ring their C/Services to see if I can get a bigger rebate.

In general, this estimating at a midpoint between actual billing points is a b....r because the customer doesn't see the estimate until he receives his 6 monthly bill - highly unlikely that you would have read the meter at the right time (altho' I had read the meter on July 1st and it was much higher than their estimate earlier in June)

I would suggest everyone checks how many units they have allowed at old rates -I bet they have set it up to be a nice little earner!!!

It's all worked out pro rata; they divide the number of units on the bill by the number of days in the bill itself, and then work out how many days before the price rise and charge that at the old rate, and then the remaining days at the new rate. It's a very fair way of working it out, I think.

Sorry Kev7891 - the point I was trying to make is that they don't do it that way for the whole 6 months .

They had actually estimated higher usage in the summer period(11 +WEEKS) than in the Spring(13+ WEEKS) so that when they then proportioned it separately for the two 3 month periods I ended up paying for more units at the final highest rate in August than I had for the lowest rate in March. It all hangs on the June "estimate".I agree that there is nothing wrong with the methodology PROVIDED THAT the estimated value for the midpoint was correct.

I got a further rebate of £1.83 which I still thought was wrong but decided enuf was enuf!