Keep Great Britain and Northern Ireland distinct
The Ofgem reference in the library covers England, Scotland and Wales, averaged for direct-debit payment. It is not a Northern Ireland rate and not a personalized regional quote. Use the actual supplier tariff for a Northern Ireland bill or a different payment method.
Build the electricity calculation
Multiply electricity kWh by the applicable unit rate, then add standing charge times billing days. Separate gas charges on a dual-fuel statement. Compare the same VAT basis and check the effective dates rather than automatically adding a familiar tax percentage.
A fixed tariff still depends on usage
A fixed unit rate does not mean a fixed final bill. An EV or overnight plan also needs the price outside the cheap window and the standing charge. Check exit fees and the duration of each price guarantee before entering a competitor offer.