Smart meter In Home Display puzzle

Staffordian11

Can anyone explain the logic used by in home displays when it comes to showing tariffs and costs?

I have a Geo display provided a few years ago when EDF fitted a smart electricity meter.

My current supplier is Octopus and my tariff has a standing charge of 49.3p and a unit cost of 21.89p

However the display says my standing charge is 54.37p and unit cost 22.99p

I have also noticed, and this is what I don't understand, that it calculates the cost incorrectly.

As an example I noticed this morning we had used (according to the display) 2.00kWh of electricity which it said was 97p. But if I calculate 2kWh on the true tariff, it comes to 93p and if I calculate it on the tariff the display thinks I'm on, that isn't 97p either, it is 95p (95.18p to be precise).

So can anyone explain what figures the display uses to calculate costs if not either the true or the displayed tariff?

It's only a matter of interest, as I don’t rely on the data for anything, I read the actual meters and use a spreadsheet to track my usage and costs, but it's just puzzling me.

Thanks for any enlightenment.

QrizB

The IHD gets its tariff data from the smart meters themselves. You should be able to find the same info in the meter menus by pressing whatever buttons your meters require pressing.

If the IHD data doesn't match your current tariff, it's because your supplier hasn't sent the tariff changes out to your meter (or possibly they sent it but your meter didn't receive it correctly). If this was important to you, you could ask your supplier to re-send it.

I can't explain the IHD's maths!

Scot_39

The IHD as above gets it's cost information from the meter - that should be set by the supplier to match your tariff - not that the likes of Octopus can realistically do that from many of their smart TOU 1/2 hourly billed tariffs anyway.

Does your meter communicate reliable with Octopus - I'd certainly maybe ask them to update the tariff prices if wrong.

But the really important thing to note is that the meter prices are not used for billing per se - even if register billed(**) - the kWh figures are the masters.

[Aside

Since I have had my smart meter and IHD - about 8 years - the pricing on it has changed several times

initially the suppliers rates were all ex VAT

the IHD price calc ignored the standing charge (I cannot see it on my old smets1 meter - it has very limited user information) but iirc could on the ihd

it then included the SC - so total correct ex VAT

the rates were then set to include VAT

(**) the rates were then sent wrongly - to me and 10,000s of other Eon customers when they renamed some tariffs like my legacy E10 - but the bills were still correct (I was sent non DD rates - so my £s figures on IHD over by c7% - took them 4 months - after yet another cap price revision to restore true DD rates)

the rates since again currently match and add up to true costs give or take odd penny - and are updated every 3 months with the new cap within days

(I have a spreadsheet that calculates my day / night split use back from it - which I have in past done daily / weekly and monthly and have checked against meter total registers in the past - so its close enough for my purposes)]

And your errors - could in part be just rounding - my IHD shows my at least historic daily use to nearest 0.05kWh - others may be different - but even thats c1.15p at your c23p rate. It also only shows my rates to 2 decimal places - not the 3 as per my suppliers bills and price notices.

The bottom line is the £s figure is best only ever seen as advisory.

However it might be worth querying with Octopus - why they haven't - at least yet - sent your meter your true rates. When did you actually switch ?

Staffordian11

Thanks for the comments.

I have always been billed correctly based, of course, on the reading from the meter itself, which I always check. And the meter reading is accurately picked up by the IHD which I look at from time to time.

I have been on my current tariff since March 2025 so it's not as if they've not had chance to update it, but as it's not causing any issues, I'm not inclined to query it.

The only thing I use the IHD for is an occasional glance at the kWh usage per day, not cost, so any tariff anomalies are irrelevant.

Still puzzled by the IHD's inability to do basic maths though :)

squirrelpie

Do the tariff rates you quote include or exclude the 5% VAT? What about the rates displayed by the IHD?

The difference would account for the disparity in unit rate, but not exactly for the standing charge.

edit to add:

if I calculate it on the tariff the display thinks I'm on, that isn't 97p either, it is 95p (95.18p to be precise

Could you show your workings for this?

Staffordian11

https://forums.moneysavingexpert.com/discussion/comment/81895144#Comment_81895144

You've cracked it, and spotted my mistake.

The Octopus figures I quoted in the original post were ex VAT.

If I multiply the IHD kWh used by my actual tariff figures the IHD cost is correct.

BUT the tariff shown on the IHD is half right and half wrong. It correctly states the unit cost as 22.99, which is the correct value including VAT but shows the standing charge as 54.37 whereas it is actually 51.77 inc. VAT.

So the IHD is calculating correctly but not using the tariff figures displayed on the IHD...

Edited to add:

Just checked the tariff details on the Landis + Gyr E470 smart meter. It gives 22.99p unit charge and 51p standing charge. Yet the linked Geo IHD shows 22.99 and 54.37. It's obviously not talking to the meter properly...

mikrt

Easy way to get octopus usage and cost is to request an "Octopus Home Mini". It'll show everything you need live on app or online.

squirrelpie

https://forums.moneysavingexpert.com/discussion/comment/81895532#Comment_81895532

For as long as you stay with Octopus anyway …

Scot_39

https://forums.moneysavingexpert.com/discussion/comment/81895319#Comment_81895319

is it just coincidence that 54.37/51.77 = 1.05 - i.e the ihd is actually adding vat itself to the displayed SC in tge meter - which is at 51p displayed vs 51.77 p possibly just the truncated sc but now sent inc vat.

i dont think the ihd snapshots tge data so might say need a power reset to relearn the new rate (my ihd doesnt appear to and updates typically a day or two after cap changes when sent fresh costs by supplier).

And the meter is actually calculating the cost the ihd displays - doing so in the meter using meter values - all vat inclusive - correctly - so ihd not doing the maths at all.

my ihd doesnt ever display my 2 unit rates or peak / offpeak registers - but it displays a total cost for the day using the mix of the two - so i assumed just gets the cost from meter itself. And its that cost i then work back to get unit split peak off peak.

I never watch it on cost say just after midnight - when daily energy use resets - maybe I should.

Staffordian11

https://forums.moneysavingexpert.com/discussion/comment/81895532#Comment_81895532

True, but I get all the data I need from my spreadsheet, or more granular detail from the Bright app. I never rely on the IHD for anything; I keep it on daily energy use and merely glance at it occasionally to judge our daily usage.

squirrelpie

https://forums.moneysavingexpert.com/discussion/comment/81899783#Comment_81899783

Everybody's use is going to be different. In my case I think the IHD is important to give my wife a better idea of what uses most power. She doesn't use apps etc.