Best answer by Tim_OVO
Updated on 29/10/20:
That smart meter and In Home Display (IHD) estimated bill won't be a total for each month. It'll provide a running total of your usage costs since they were installed, or since your last tariff change.
They don't link up with your billing system. The smart meter and IHD communicate with each other, giving you live usage info and historic comparisons. The smart meter also sends us a load of readings, which our billing platform and your online account gobbles up, turning them into great usage info. If your smart meter sends us your readings every 30 minutes, the online usage section is great. See our guide on this here. We also have a guide on monthly charges here.