Back Billing: How Far Back a Supplier Can Charge

A back bill is a bill your supplier asks you to pay when they have not accurately charged you for energy you have already used¹. It typically arrives as a single, often large, "catch-up" charge covering months or years of gas or electricity that was never properly billed, and suppliers are likely to demand payment in one lump sum within a set time of the bill date². The protection against this is the back billing rule: in most circumstances a supplier cannot charge a household or microbusiness for energy used more than 12 months ago¹.

The rule is not a courtesy from suppliers. It is written into their licences as Standard Licence Condition 21BA, and Ofgem has stated plainly that any consumer energy supply contract that does not reflect the requirement breaches the condition and is unlawful, with any incompatible term unenforceable³. The limit applies to all payment methods, regardless of payment type, meter mode or meter arrangements, and it also covers Direct Debit adjustments relating to charges over 12 months old⁴.

Back bills explained: meaning and causes

Ofgem's definition is simple: "Your electricity or gas supplier will ask you to pay a 'back bill' when they have not accurately charged you for energy"¹. Independent guidance describes the same thing as a "catch-up" bill sent when you have been incorrectly charged, covering extra energy used but not charged for². On heat networks, where heating is supplied through a communal system rather than a gas boiler, the same term is used: a bill for heat you have used in the past⁷.

Back bills arrive for a cluster of related reasons, and nearly all of them sit with the supplier rather than the customer:

• The supplier never sent a bill at all for a period of use².
• Bills were based on estimated readings that turned out to be lower than actual consumption².
• The supplier kept sending estimated bills even after the customer supplied accurate meter readings².
• The monthly Direct Debit was set too low, so payments never covered what was being used².
• The account was in dispute, transferred between suppliers, or otherwise left unbilled for a period.

The size of the shock is the problem. Because the supplier is likely to demand payment in one lump sum within a set time of the bill date², a household that has been under-billed for two or three years can suddenly face a bill running to hundreds or thousands of pounds, arriving without warning and alongside the normal ongoing bill. The back billing rules exist precisely because Ofgem judged that customers should not bear the consequences of a supplier's own billing failure over an extended period.

The 12-month cap on retrospective charging

The core rule is that you do not have to pay for energy you used more than 12 months ago, provided certain conditions are met. Ofgem sets out three conditions, all of which point to the supplier's failure rather than yours⁸:

• You have not had an accurate bill for that energy before, even if you asked for one.
• You have not been told what you needed to pay through a statement of account.
• Your Direct Debit amount was previously set too low to cover what you needed to pay⁸.

The rule is symmetrical in an important way: it does not matter whether the supplier sent no bills, sent estimated bills, or set a Direct Debit that quietly built up a shortfall. In each case the protection cuts off the chargeable period at 12 months². The Energy Ombudsman summarises the licence position as follows: an energy supplier cannot charge domestic or microbusiness consumers for energy used, or for charges, more than 12 months old where the failure was the supplier's⁹.

The legal machinery behind this is Standard Licence Condition 21BA. Ofgem's open letter on charge recovery states that the condition protects domestic and microbusiness consumers from being charged for unbilled consumption over 12 months old, except in cases of obstructive or manifestly unreasonable behaviour, and that charge recovery action may only be taken in respect of units consumed or standing charges accrued within the 12 months before the action³. Suppliers are required to reflect the requirement in their consumer supply contracts, and any term that does not is unenforceable³.

One adjacent limit is worth knowing about, because households on heat networks sometimes confuse the two. Where heating charges are recovered through a service charge under the Landlord and Tenant Act 1985, Section 20B gives a landlord 18 months to notify the consumer of incurred costs¹⁰. That is a housing law deadline, not the energy back billing rule, and Ofgem's heat network guidance treats the two separately.

Exceptions allowing charges beyond 12 months

The protection is not absolute. There are three main routes by which a supplier can lawfully charge for energy older than 12 months.

A bill was sent in time but never paid. The rules do not apply if the supplier sent you a bill before the year passed and you did not pay it; in that case the supplier can still charge you for it, even after 12 months has gone by¹¹. Ofgem's licence guidance gives this as an example of an exception: where the supplier had already sent an accurate bill but the customer has not paid the relevant charges³. The protection covers unbilled energy, not unpaid bills.

You behaved unreasonably. Ofgem lists the behaviour that removes the protection⁸:

• Stopping your supplier from billing you accurately, including by blocking access to your meter.
• Ignoring requests for payment from your supplier.
• Stealing electricity or gas⁸.

Independent guidance adds two further examples: blocking meter readings at the property more than once without good reason, and knowingly using gas or electricity without informing the supplier². Where the customer is found to be at fault, the supplier can back-bill for up to six years⁵. Which? states the position in one line: energy firms are banned from back-billing you for energy used more than 12 months before the error was detected, if it is the supplier's fault; if you were at fault, they can back-bill you for up to six years⁵.

The charges fall outside the rule's scope. On heat networks, charges recovered through a service charge are not covered by the 12-month back-billing limit¹⁰. And a single failure to provide a meter reading does not, on its own, remove the protection: Ofgem has stated that a customer's failure to provide a meter reading will not absolve the supplier from the backbilling limit, though suppliers should keep records of their attempts to obtain one⁴.

Meter readings, estimates and the meaning of accuracy

The whole edifice rests on the word "accurate", so it matters that estimated bills do not count as accurate billing. Ofgem's work on consumer outcomes treats estimated meter reads as not accurate where they differ from actual consumption, and its proposed monitoring includes testing regular bills to check that actual readings match real consumption and that charges are applied correctly¹⁴. The practical implication is that a run of estimated bills does not start, or restart, the 12-month clock: the period remains unbilled for back billing purposes until an accurate bill is issued.

You can check your own bills for this. The Energy Ombudsman advises looking for an "E" or the word "estimate" on the bill to identify whether the reading has been calculated rather than taken⁹. If your supplier has continued to send bills based on estimated readings even after you have sent accurate readings, the back billing protection still applies².

The Ombudsman's own case studies show how this plays out. In one dispute over usage based on estimated meter readings, it required the supplier to re-bill the account, provide an apology, and pay a time and trouble award to acknowledge poor account management and poor complaint handling¹⁵. The Energy Ombudsman also notes, in its guidance on billing concepts, that common industry ideas such as back billing and metric versus imperial meters will be unfamiliar to the majority of consumers, which is part of why suppliers are expected to explain them clearly¹⁶.

Two wider points frame the scale of the issue. Energy UK reports that the accuracy of bills has risen to a joint record high, and that back billing complaints remain at low or comparable levels compared with recent years, at 4 to 5% of total complaints to the Ombudsman¹⁷. At the same time, Ofgem's consultation on consumer outcomes records that 38% of a sample of Money Advice Trust billing cases involved catch-up billing¹⁴, which suggests that where billing does go wrong, it goes wrong in a way that accumulates debt. For more on how estimates work and how often meters must be read, see meter readings and estimated bills and estimated bills explained.

Settling an accurate back bill over 12 months

The protection limits how far back a supplier can charge; it does not cancel what is owed within the limit. Ofgem is explicit: "you need to pay any accurate bill you have been sent by your supplier, including back bills"¹. A back bill that complies with the 12-month rule is a legitimate charge for energy actually used, and the government's smart meter rights and expectations material sets out the underlying principle: households receive accurate bills and only pay for the energy they use¹⁸.

What the rules do change is the shape of repayment. Independent guidance is consistent that a supplier should offer a payment plan allowing you to repay any debt over the same length of time it took to build up⁵. If you were under-billed for eight months, an eight-month repayment plan is the benchmark; a demand for the whole sum at once is not what the framework contemplates, even though suppliers are reported as likely to demand payment in one lump sum within a set time². Your supplier should also make the back billing rules clear in your contract's terms and conditions².

For prepayment customers the mechanics differ. Where credit is applied to a prepayment meter, you will need to pay back any credit you get when you next top up, and your supplier must work with you to agree a payment plan¹⁹. The broader framework for arrears is covered in energy debt and repayment plans, and the rules on repaying debt through a prepayment meter in prepayment meter debt repayment.

If your supplier has already taken money for charges the rules did not permit, the remedy is direct: Ofgem states that if the supplier has not followed the back billing rules, they will refund any money taken in error¹. You can challenge a back bill you believe covers energy used more than 12 months ago by writing to the supplier, and making a formal complaint if they do not accept the challenge².

Scope of the rules: homes, microbusinesses and regions

The rules apply to households and microbusinesses¹. The Energy Ombudsman states the licence position in the same terms: an energy supplier cannot charge domestic or microbusiness consumers for energy used or for charges more than 12 months old where the fault is the supplier's⁹. Ofgem's licence guide likewise applies the relevant conditions to suppliers of domestic consumers and some microbusinesses²⁰. Larger businesses are outside it: Ofgem's consumer outcomes consultation notes that only the meter read condition applies to all non-domestic consumers, with the backbilling condition applying to microbusinesses¹⁴.

Territorially, the licence conditions cover Great Britain, and Ofgem's heat network guidance states that its back-billing authorisation condition applies across Great Britain, limiting back billing to 12 months across all heat networks unless there are conflicts with existing housing legislation¹⁰. Citizens Advice marks its England guidance as applying to England, with equivalent advice published for Scotland and Wales¹¹. Northern Ireland is a separate market with its own supplier arrangements, covered in energy bills in Northern Ireland.

Heat network consumers have a parallel protection with its own edges. The back-billing authorisation condition applies only to domestic and microbusiness consumers, so non-domestic consumers are not covered¹⁰. Heat network consumers in England and Wales living in properties covered by the Landlord and Tenant Act 1985 fall under a specific exclusion, because Section 20B of that Act provides its own 18-month notification regime for service charges²¹.

The rules also survive supplier failure. When a supplier goes bust, the back billing rules were part of your contract with the old supplier, because they are part of the Standard Licence Conditions, and they apply to all the companies that might send you an energy bill²². Ofgem has stated that insolvency practitioners are required to abide by the same regulatory requirements and contractual duties as energy suppliers when dealing with consumers, including the Backbilling Requirement, and that debt collection agencies collecting a supplier's consumer debt are bound by the same requirements³.

Regulation, redress and the source of the rules

The rules were created by Ofgem in 2018, when it banned suppliers from back-billing customers beyond 12 months, with the exception of consumers who actively prevent suppliers from taking or receiving accurate meter readings, for example by tampering with or obstructing access to the meter¹³. They now sit in Standard Licence Condition 21BA of the gas and electricity supply licences, and suppliers must reflect the requirement in their consumer contracts; a contract that does not is unlawful and its incompatible terms unenforceable³. Suppliers are expected to inform consumers of the backbilling limit in plain and intelligible language⁴.

Ofgem polices this actively. It has stated that it will review suppliers' compliance, investigate further where it believes the Backbilling Requirements are not applied correctly, and take action to ensure compliance and provide redress to disadvantaged consumers⁴. The wider conduct framework reinforces this: since August 2013 energy suppliers have been subject to enforceable Standards of Conduct requiring them to treat customers fairly across all interactions, including complaints²³, and complaints handling standards regulations have applied to complaints from domestic customers and microbusiness consumers²⁴.

The complaint route for an individual household runs in a fixed order. Ofgem advises contacting your supplier about late, incorrect or missing bills, back billing, overcharging, faulty meters, poor service and refused credit refunds²⁵. Which? describes the same ladder: complain to the supplier, escalate internally, and then take the case to the Energy Ombudsman once eight weeks have passed or deadlock is reached⁵. The full process is set out in how to complain about a back bill.

The volume of disputes gives a sense of scale. The Energy Ombudsman received 3,218 disputes relating to back-billing in 2024, around 3% of its total complaints that year⁶. A parliamentary committee review found that back-billing issues are not systemic but still affect thousands of energy customers and need to be addressed⁶. Energy UK reports back billing at 4 to 5% of total complaints, at low or comparable levels against recent years¹⁷.

The rules themselves are under review. Ofgem's work on debt and billing standards discusses proposals such as making monthly billing the default and reviewing the back-billing rules, with policy options on billing waiting for that work to conclude²⁶, and its consumer outcomes consultation lists the backbilling condition among the rules in scope for implementation¹⁴.

What households gain from the protection, and its limits

What the back billing rules deliver is a hard limit on one specific form of dependence: the exposure a household has to its supplier's own administrative failure. Without them, a supplier that under-billed for three years could convert its error into a household debt at any moment, on the supplier's timetable and in one lump sum². With them, the maximum exposure from supplier fault is 12 months of unbilled energy, repayable over the period it built up⁵, and money taken in error must be refunded¹. That is a genuine constraint on the supplier's power over the household's finances, and it is enforceable: the licence condition makes non-compliant contract terms unenforceable³.

What the rules do not do is equally plain. They do not write off energy debt that was properly billed; a bill sent in time but unpaid remains chargeable however much time passes¹¹. They do not protect a customer who obstructs the meter, where the exposure extends to six years⁵. They do not cover larger businesses¹⁴, and on heat networks they do not reach charges recovered through a service charge¹⁰. And they do nothing about the underlying fragility that produces back bills in the first place: a household that does not check its bills, submit readings or notice an "E" next to the meter reading⁹ can still spend a year accruing a debt it will have to pay.

The practical independence lesson is that the rules are a backstop, not a substitute for attention. A household that reads its own meter, checks that bills are based on actual readings, and queries a Direct Debit that looks too low against its usage will rarely need the protection at all. The pages on how to read a gas or electricity meter, direct debit payments and credit balances and why a direct debit may be set too high or too low cover the habits that keep a bill accurate in the first place. For the wider picture of what a bill contains and how the price cap sets the rates applied to it, see what makes up a UK energy bill and the pillar guide to energy bills and the price cap.