thank you all !!!!! now everything is clear.

Shorter version :)

(annual allowance divided by 365) to get a daily Tier 1 allowance

multiply by the number of days your bill actually spans

On an imperial gas meter 1 unit is about 32 kWhs
On a metric gas meter 1 unit is about 11.2 kWhs
On an electricity meter 1 unit is 1 kWh

Convert your meter readings to kWhs as above (those are approximate numbers for gas - exact sum is on your bill.)

For gas, your 2680 kWh is per annum. In a quarter, that will be 2680 / 4 or 670 kWh. So the first 670 kWh cost 7.145p the rest cost 3.396p. 7.145p - 3.396p = 3.749p. So that's an extra 3.749p for the first 670 kWhs each quarter. 670 x 3.749p is £25.12 per quarter or £8.37 per month.

So the cost of your gas is ( 8748.93 x 3.396p ) + £25.12 or £297.11 + £25.12 or £322

But to answer your actual question: as it is a 94 day quarter, the number of Tier 1 units will be a bit more. (2680/365) per day times 94 days or (2680/365) x 94 = 690. So for this bill, about 690 kWhs will be charged at the higher rate.

Hi!!! can somebody please help me understand how utility companies calculate the kwh in 1st/2nd rate price. im with BG and my tarriff is

Gas - 7.145p up to 2680kwh then 3.396p for the rest

Electric - 26.081p up to 500kwh then 11.715p for the rest

its says we've used 8748.93 kwh over 94 days for gas and 1290.00 kwh over 94 days for electric.how do they get the no. of kwh on the 1st rate??? hope to hear from anybody. thank you in advance.