Energy Back-Billing Rules: The 12-Month Rule Explained

If your energy supplier suddenly sends a large bill for gas or electricity used over a year ago, Ofgem's back-billing rule may protect you. Here is how the 12-month rule works, when it does not apply, and how to challenge an unfair back bill.

The 12-Month Back-Billing Rule

The back-billing rule is a condition of every domestic energy supplier's licence, set by the energy regulator Ofgem for Great Britain. It means a supplier cannot bill you for gas or electricity you used more than 12 months ago if it failed to bill you correctly at the time and the error was not your fault.

The rule exists because suppliers sometimes go a long time without sending an accurate bill, then land the customer with a large "catch-up" bill covering a year or more of energy use all at once. The 12-month rule caps how far back that catch-up bill can reach, so you only have to pay for the most recent 12 months of the energy covered, not the whole backlog.

The rule applies to domestic customers and microbusinesses (very small businesses) supplied by a licensed gas or electricity supplier in Great Britain.

When the Rule Applies

The back-billing rule is triggered by a supplier's own failure to bill you correctly, not by any fault of yours. Typical situations include:

• The supplier billed you using estimated readings for an extended period and never corrected them against your actual usage.
• There was a long delay between meter reading visits or contacts, so the supplier only realised its records were wrong much later.
• An administrative error meant you were never sent an accurate bill for energy you had already used, and the mistake only came to light when the supplier reviewed your account.
• You were not told what you owed through a statement of account, or your Direct Debit was set too low to cover what you needed to pay.

In all of these cases, if the supplier's own failure means it is only now trying to bill you for energy used more than 12 months ago, you only have to pay for the energy used in the 12 months before the back bill was issued. Anything older than that falls outside what the supplier is allowed to charge.

Exceptions: When You Can Still Be Back-Billed Beyond 12 Months

The 12-month rule protects you when the billing delay is the supplier's fault. It does not protect you if you are the reason accurate billing was not possible. A supplier can still back-bill you beyond 12 months if you:

• Obstructed access to the meter, for example repeatedly refusing to let the supplier or its agent in to take a reading.
• Ignored requests for payment from the supplier.
• Acted in a way that is "manifestly unreasonable", which includes things like tampering with the meter or stealing energy.

Ofgem has said that you will not be at fault just because you did not provide meter readings. If none of these apply to you, and the delay was down to the supplier's own systems or processes, the 12-month cap should apply.

How to Challenge a Back Bill

If you receive a bill for energy used more than 12 months ago and believe none of the exceptions apply to you, take these steps:

1. Contact your supplier in writing (email or a letter you keep a copy of), explain that you believe you are protected by the back-billing rule, and ask for the bill to be capped at 12 months' worth of energy.
2. Keep records of the correspondence, including dates, any meter readings you gave, and any earlier bills or estimates the supplier sent you.
3. Ask for a repayment plan if you do owe money for the 12 months that are chargeable. Suppliers will usually let you spread repayment over a period similar to the length of time the bill covers.
4. Escalate to the Energy Ombudsman if your supplier will not resolve the complaint, either because 8 weeks have passed with no resolution or because you have received a final "deadlock" letter. The Energy Ombudsman is free and independent, and can order a supplier to reduce or write off charges that breach the back-billing rule.

For the general complaint route that applies beyond energy issues too, including timelines and when a company must point you to an ombudsman, see how to complain about a company.

Northern Ireland Is Regulated Separately

Ofgem's back-billing rule covers Great Britain (England, Scotland and Wales). In Northern Ireland, energy suppliers are regulated by the Utility Regulator, not Ofgem, and complaints go to your supplier first, then to the Consumer Council for Northern Ireland, rather than the Energy Ombudsman. Since 1 October 2020 the Utility Regulator has limited back bills to 13 months for domestic and microbusiness customers where the supplier was at fault. The rules and exceptions are set separately from Ofgem's, so check with the Utility Regulator if you are billed in Northern Ireland.

Free Help

You do not need to pay anyone to challenge a back bill. The Citizens Advice consumer service gives free, independent guidance in England and Wales on 0808 223 1133 (Welsh language: 0808 223 1144), Advice Direct Scotland gives the same help in Scotland on 0808 164 6000, and the Energy Ombudsman investigates unresolved complaints against energy suppliers for free.

This article is general information about energy back-billing rules in Great Britain, not legal or financial advice, and does not cover every possible billing scenario. For free, independent guidance on a specific back bill, contact the Citizens Advice consumer service on 0808 223 1133 (England and Wales), Advice Direct Scotland on 0808 164 6000 (Scotland) or the Energy Ombudsman. For related rights, see consumer rights under the Consumer Rights Act 2015 and subscription and auto-renewal rules. For the wider picture, see the UK Consumer Rights hub and the United Kingdom hub.

Frequently Asked Questions

How far back can an energy supplier bill me?

Under Ofgem's back-billing rule, a supplier cannot bill you for gas or electricity used more than 12 months ago if it failed to bill you correctly and the error was not your fault. This applies to domestic customers and microbusinesses in Great Britain.

What counts as a supplier's billing error under the back-billing rule?

Common causes include estimated bills that were never corrected against actual usage, a long delay between meter readings or contacts, or an administrative mistake that meant you were never sent an accurate bill for energy you had already used.

Can I still be billed for energy used more than 12 months ago?

Yes, if you prevented the supplier from billing you accurately, for example by refusing access to your meter for a reading, ignoring requests for payment, or acting manifestly unreasonably such as tampering with the meter or stealing energy. Not providing meter readings does not on its own put you at fault.

What should I do if I get a back bill for more than 12 months of energy?

Complain to your supplier in writing, explain that you believe you are protected by the back-billing rule, and ask for the bill to be capped at 12 months. Keep a copy of your complaint and any response you receive.

What if my supplier will not reduce the back bill?

If your supplier does not resolve the complaint within 8 weeks, or sends you a final deadlock letter, you can take the complaint to the Energy Ombudsman for a free, independent decision.

Does the back-billing rule cancel a bill I already received but did not pay?

No. The rule only limits how far back a supplier can charge you for energy it failed to bill correctly at the time. If you were sent an accurate bill and simply did not pay it, that is an unpaid debt, not back-billing.

Does the 12-month rule apply in Northern Ireland?

Not directly. Ofgem's back-billing rule covers Great Britain. In Northern Ireland, energy suppliers are regulated by the Utility Regulator, which limits back bills to 13 months where the supplier was at fault. A Northern Ireland back-billing complaint goes to your supplier first, then to the Consumer Council for Northern Ireland.