I use the online Portal to monitor my usage and costs each day for both electricity and gas. While there is, often a slight difference between the Day Tab Total and the Month Tab Total, it is not, usually as large as it was for my usage yesterday (23rd November 2025). I wonder if anyone can suggest a possible reason for this disparity?
The figures should be very nearly the same. However, they’re probably derived from different datasets, so if there’s a fault in one of them, a discrepancy could arise. Again, I can’t really say anything much about gas, but the missing usage data you’ve been drawing attention to could be the reason for the difference you see. There is something that is preventing some usage data packets being transmitted to the CH, but the midnight register readings are getting through reliably.
At a guess, one is the sum of the half-hourly quantities while the other is the difference between midnight register readings, all converted at some undisclosed CV.
I suspect that you are right as the sum of the half hourly readings is approximately the sum of the usage on the Day Tab. The sum on the Month Tab is approximately (using the crude approximation that 1 gas unit is equal to 11.2 kWh (for a metric meter)) what I would expect it to be from the difference in the midnight readings converted using a calorific value which OVO never see fit to share directly with its customers. This is the really useful (like a chocolate teapot) advice about converting metered units to kWh that appears on every gas bill.
… a calorific value which OVO never see fit to share directly with its customers.
OVO are rather proud of their ‘live billing’ system, which means that the account balance is updated every day to reflect the day’s usage and payments. I don’t know, but I suspect that this means that a day’s gas volume is converted to energy using the day’s CV as published the following day. Each day’s CV is thus different, so there’s no practical way of showing it on bills. You can always reverse engineer the average CV over a period from the given m³ and kWh figures for the period.
Some meters and IHDs show kWh values for gas usage. These will be converted using a constant average CV, something like 39.5 MJ/m³.
Again that discrepancy is something that I notices a couple of years ago.
Mne isn’t usually that much different though, for example the daily figure given for yeaterday is 32.97 kWh, whereas on the monthly chart it’s 32.39 kWh.
I put it down to different CV values being used to calculate the values shown in each of the modules.
(and then possibly when the actual value becomes available it being recalcuated for one but not the other?)
The webpages have been created in a modular fashion and there are visible discrepances in the calculations used, or the figures used in those calculations*, in each module at times.
Then there is a possibly foran extra discrepancy because the metering is to 3 DP’s whereas the figures displayed online are only 2 DP’s, so either a ‘rounding’ or a‘truncating’ error gets introduced.
And then possibly another discrepance may be introduced bt the metering offset that we have been discussing in your other thread.
After I got a new SMETS2 gas meter last November I did for a month of three get the CV values for each day and then using a spreadsheet calculate the ‘actual’ kWh for the start and end of the day meter readings (to 3 DP).
They were ‘close enough’ to only make a few pennies a year difference to billing, so I ceased doing it.
Yes the various discrepances can be annoying, but I’ve found (as Firedog also has) that trying to explain why they are happing and get someone to do something about correcting them just meets a dead end at OVO, if they can understand what we have found then they just don’t see it as being an issue worth spending resources on.
TBH with such modular coding it can be a PITA trying to get all the calculations in overlapping modules the same, particularly if they were done by different developers at different times.
Plus you always run the risk of ‘breaking’ something that currently runs OK, but not quite as joined-up as it could be.
This is what actually appears on our gas bills with the conversion “explanation” beside it. Many people only use their monthly bills to show whether their meter readings have been recorded correctly and that they are being charged correctly. Expecting customers to go to an outside website to find a CV and then decide which day, once they have worked out the area they live in, has actually been used to calculate their personal CV is, I feel, more complicated than it should be. Which date should I choose? Across the “life” of this bill, the CV in my area varied between 38.9 and 39.3.
There were probably 31 different CVs used to arrive at the figure of 267.872. You can work out the average over the period: 267.872 x 3.6/1.02264 x 24.089 = 39.146 ≈ 39.1. That fits nicely within your [ 38.9 | 39.3 ] bracket.
If you really needed to, you could in your worksheet record each day’s meter reading and each day’s CV from National Gas to work out each day’s usage of energy. The NG value can change from the one first published, so the day’s calculation can’t be done accurately until perhaps a day later. You could do this for a month just to satisfy yourself that OVO is doing its sums properly - or not, I suppose.
Morning
I hope you’re well and thanks for your post. I’m unsure as to the reasons behind the monthly usage not being accurate, and I’ve raised this internally.
I’ll let you know if I hear back about this.
I’m raising this to our IT team.
It seems like constant issues for everyone involved. I've given up at this point, as it's clear they have major internal problems and aren't being honest. My bills and readings are consistently incorrect, and the amounts on my emails and online account statements never match up. They’ve even claimed I didn’t have an account until September last year, despite having been with them since 2023, with statements to prove it. One previous statement even said I owed £5,000 for a single month! I live in a 3-bedroom house with one adult and two children—hardly the kind of usage that would result in that amount.
If, after two years of complaints and multiple attempts to contact them, they still can’t explain or provide accurate bills, then I simply don't understand how my direct debit has been stopped. This has been going on for far too long.
It’s enough to post once. I’ve responded in your other thread and asked the forum moderators to remove your post here and this reply to it to avoid duplication of effort on the part of those who try to help you.
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