calculations — Bulb Community

# calculations

Please can you explain calculations as displayed on the bills please. E.G. if it says a customer has used '90 kWh @ 12.91 p/kWh', does that mean you multiply 90 by 12.91? If so the total should be 11.62 but on my bill I have been charged £11.66. Please explain as all the calculations on all my bills don't seem to match the results of your equation.

• BJS_704A said:

Please can you explain calculations as displayed on the bills please. E.G. if it says a customer has used '90 kWh @ 12.91 p/kWh', does that mean you multiply 90 by 12.91? If so the total should be 11.62 but on my bill I have been charged £11.66. Please explain as all the calculations on all my bills don't seem to match the results of your equation.

I can almost guarantee it is because Bulb don't provide the correct number of decimal places which they use in their calculation of your bill. This is an issue which a number of us fellow customers have raised on this forum.
• BJS_704A said:

Please can you explain calculations as displayed on the bills please. E.G. if it says a customer has used '90 kWh @ 12.91 p/kWh', does that mean you multiply 90 by 12.91? If so the total should be 11.62 but on my bill I have been charged £11.66. Please explain as all the calculations on all my bills don't seem to match the results of your equation.

Just to second what @Allanr said - yes you're doing the calculation correctly. The problem is you're not provided with figures to the necessary precision for Bulb's calculations to be reproducible.
• edited July 12
@BJS_704A Maybe you can persuade Bulb to display on bills and tariffs the actual figure they use.
@Allanr, @Hooloovoo, @scudo and I, plus others, have thus far failed.
• edited July 12
@Eleanor

I searched and searched and found the relevant community thread regarding the previous decimal places discussion.

It still isn't included in the Roadmap (last issued 10 May 2019) although I think it was promised to be updated monthly?

• edited July 12
No doubt additional decimal places and rounding conventions do play a part but I suspect that Bulb might also add an arbitrary fraction of a kWh to the usage to reflect that most meters will actual lybe between whole numbers when readings are taken. I can reconcile my own discrepancy if I add 0.2 kWh to my metered usage. At any rate it is deeply unsatisfactory for Bulb to show what appears to be an obvious arithmetical error on the face of customer statements.
• No doubt additional decimal places and rounding conventions do play a part but I suspect that Bulb might also add an arbitrary fraction of a kWh to the usage to reflect that most meters will actual be between whole numbers when readings are taken. I can reconcile my own discrepancy if I add 0.2 kWh to my metered usage.

I find it totally inconceivable that Bulb would add any arbitrary fraction of a kWh?

There would be no need to do this since meter reading over time would cancel out any "in between readings"

I'm willing to be proved wrong, but the problem is due to the number of places used internally by Bulb compared to what is shown on the statements.
• Allanr said:

I find it totally inconceivable that Bulb would add any arbitrary fraction of a kWh?

I agree I very much doubt Bulb are doing this.

Interestingly I did have a sort-of related problem. As we know meter readings are all rounded down by the action of taking only the integer component of the reading. However it turns out readings from my smart meter are logged at the full floating point precision supplied by the meter AND my statement usage is calculated to this precision. But the readings on the statement are shown rounded to integers, and this leads to the inconsistent values @Eleanor at Bulb described for me here where 1254-1070 apparently equals 183.

I can't remember if @christos_1 is using smart meter readings.
• edited July 12
I can't remember if @christos_1 is using smart meter readings.
Actually all my recent readings are estimated - but I do have a Bulb smart meter. These discrepencies are not always in Bulb's favour. Last December I used 378 kWh at a rate of 12.63p per kWh. Bulb's charge was £47.69 which should have been £47.74 to be arithmetically correct using the figures given. To get £47.69 for 378 kWh implies a rate of 12.6164p per kWh but that rounds to 12.62 not 12.63.
• I can't remember if @christos_1 is using smart meter readings.
Actually all my recent readings are estimated - but I do have a Bulb smart meter. These discrepencies are not always in Bulb's favour. Last December I used 378 kWh at a rate of 12.63p per kWh. Bulb's charge was £47.69 which should have been £47.74 to be arithmetically correct using the figures given. To get £47.69 for 378 kWh implies a rate of 12.6164p per kWh but that rounds to 2.62 not 2.63.
How it rounds is also affected by whether you add the VAT first or at the end. Bulb correctly do all the calculations and then add 5% VAT. But all the prices are listed inclusive of VAT and at insufficient precision to begin with, never mind after dividing by 1.05, so you never really know the true price. Does that account for the missing penny on your unit rate?
• Not really
• My latest statement is shown as 173 kWh x 12.63 p per kWh = £21.84 (which I calculate as 2184.99p or £21.85 - 1 penny favourable to me)
My previous statement showed 182 kWh x 12.63 p per kWh = £23.01 (which I calculate as 2298.66p or £22.99 - 2 pence adverse to me)

I get that 12.63 p per kWh is a simplification of a more exact figure with more decimal places, but I don't understand why the resulting discrepancies are in opposite directions? This part of the statement is above the point where VAT is added so I can't see how that would come into it..

It is possible, I suppose, that the quantities of kWh are simplifications of more exact decimal numbers but they are Bulb estimates not actual smart meter readings.

The differences are trivial of course, but I would like to understand them.