Energy back-billing rules: you can't be billed for energy used over 12 months ago

Great Britain · Rules checked 24 October 2026 · Not legal advice

Free tool: Back-billing calculator. Enter the bill date and the period charged to find the 12-month line.

If your gas or electricity supplier hasn't billed you correctly and then sends a big "catch-up" bill, the back-billing rule limits how far back it can go. It is Standard Licence Condition (SLC) 21BA in every supplier's supply licence, for gas and for electricity, and has applied since 2018.

What the rule says

When a supplier bills you, or otherwise tries to recover charges (including through a prepayment meter), it can only charge for:

• energy that could reasonably be considered to have been used within the 12 months before the date of that bill or action; and
• standing charges and other supply charges built up in those same 12 months.

So for a bill dated 10 March 2026, the supplier can usually only charge for energy used from 10 March 2025. Anything older should be written off. Use the back-billing calculator to find your line.

When the rule doesn't help

• You were billed correctly before and didn't pay. The supplier can keep chasing a bill it sent properly at the time.
• Obstructive or manifestly unreasonable behaviour stopped it billing you correctly. Ofgem's back-billing page gives examples: blocking access to your meter, ignoring requests for payment, or stealing energy. See what counts as unreasonable.

What Ofgem has told suppliers

In a 2020 open letter, Ofgem said the rule applies to every payment method and meter type, including prepayment and smart meters, that customers aren't responsible for spotting billing errors, and that a customer not giving a meter reading does not, on its own, take the supplier outside the rule. It listed common causes of back-bills: no bills at all, inaccurate or estimated bills, a Direct Debit set too low, and prepayment meters not updated.

What to do

1. Find the bill date and the earliest date it charges for.
2. Work out the 12-month line with the calculator.
3. Write to the supplier quoting SLC 21BA. Ask it to remove the older charges, give a breakdown by reading, and pause collection of the disputed part.
4. Keep paying for current use and the part you accept.
5. If it refuses, make a formal complaint, then go to the Energy Ombudsman after 8 weeks.

Questions