If a letter has just landed from your energy supplier demanding hundreds or thousands of pounds for energy used months or years ago, don't reach for the bank card yet. 

Ofgem's back billing rules exist for exactly this situation, and in many cases they mean you don't have to pay the full amount, even if the usage really was yours. 

This guide explains what back billing is, how Ofgem's 12-month rule works for businesses, when suppliers can still chase older charges, and what to do if a back bill lands on your desk. 

Five-point summary of our business energy back billing guide 

• Back billing is when a UK energy supplier issues a delayed or corrected bill for previously unbilled or under-billed energy usage. 
• Ofgem’s 12-month rule limits suppliers from charging microbusinesses for energy used more than 12 months ago if the billing failure was the supplier’s fault. 
• The rule applies to microbusinesses that meet thresholds for employees, turnover, or energy consumption. 
• Suppliers can bill beyond 12 months if the customer caused the delay, such as blocking meter access, ignoring requests, or tampering with equipment. 
• Businesses can challenge invalid back bills, escalate complaints, and take disputes to the Energy Ombudsman if unresolved. 

What is back billing? 

Back billing happens when your energy supplier issues a bill for gas or electricity that should have been charged at the time but wasn't. 

Rather than billing you monthly or quarterly as usual, the supplier goes back and recalculates what you owe, often based on an actual meter reading that shows your estimated bills were too low. 

It's a familiar problem. Suppliers rely on estimated readings whenever they can't get an actual one, because a site is vacant, a meter is hard to access, or a customer hasn't sent in readings. 

Estimates can drift a long way from real usage over time, and when the true figure finally comes to light, the gap between what you've paid and what you actually owe can be substantial. 

What is a "catch-up" bill? 

A catch-up bill is another name for a back bill: a single invoice that covers a backlog of unbilled or under-billed energy, sometimes going back several years. It's called a catch-up because the supplier is trying to bring your account in line with your real consumption in one go, instead of the gradual, predictable billing you'd normally get. 

The scale of these bills can be serious. When Ofgem introduced its formal back billing cap, it put the typical catch-up bill at over £1,000, enough to cause real cash flow problems for a small business that wasn't expecting it. 

What are Ofgem's back billing rules? 

Ofgem's back billing rules are a set of protections written into every UK energy supplier's licence conditions. They limit how far back a supplier can go when correcting a billing error, so customers aren't landed with an unmanageable, backdated bill through no fault of their own. 

The 12-month rule explained 

The core of Ofgem's back billing rules is simple: a supplier can't charge you for energy used more than 12 months ago if the failure to bill you correctly at the time was down to them. This is usually called the 12-month rule, and it applies regardless of your payment method, meter type, or billing arrangement. 

In practice, this means a supplier can typically only claw back 12 months' worth of energy from the date the corrected bill is issued, not from whenever the underbilling began. 

If a supplier discovers in 2026 that it failed to bill you properly since 2023, the rules mean it can usually only charge for the most recent 12 months of that period, not the full three years. 

It's worth being clear about what the rule doesn't do. It doesn't wipe out debt you've already been correctly billed for and simply haven't paid. 

Back billing rules apply to charges you were never billed for in the first place, not to overdue invoices sitting unpaid in your inbox. Mixing up the two is one of the most common reasons businesses either overpay unnecessarily or underestimate what they genuinely owe. 

Does the rule apply to businesses? 

Yes, but not to every business. Ofgem's back billing rules explicitly cover domestic energy consumers and microbusinesses. If your company is classed as a microbusiness, you get the same 12-month protection as a household customer. 

Ofgem defines a microbusiness as one that meets any of the following: 

• Fewer than 10 employees (or full-time equivalent) and an annual turnover or balance sheet total of no more than £2 million, or 
• Annual electricity consumption of no more than 100,000 kWh, or 
• Annual gas consumption of no more than 293,000 kWh. 

A business only needs to meet one of these criteria to qualify, and the consumption thresholds apply separately to gas and electricity, so it's possible to be classed as a microbusiness for one fuel but not the other. Larger businesses that fall outside this definition aren't automatically protected by the formal 12-month cap, though Ofgem's broader Standards of Conduct still require suppliers to bill fairly and transparently. 

When can a supplier still back bill you beyond 12 months? 

The 12-month rule isn't unconditional. Ofgem built in specific exceptions for situations where the customer, rather than the supplier, is responsible for the billing delay. If any of the following apply, a supplier can usually recover the full amount owed, even if it covers several years. 

Blocking access to your meter 

If your business has repeatedly stopped the supplier reading the meter, for example by refusing site access or locking gates, this counts as unreasonable behaviour under Ofgem's rules. Suppliers are entitled to rely on estimates in this situation, and the 12-month cap won't apply if that obstruction is the reason the bill fell behind. 

Ignoring requests for meter readings or payment 

Suppliers usually ask customers to submit their own readings between visits, particularly for meters that aren't smart-enabled yet. If your business consistently ignored these requests, or didn't respond to repeated requests for payment on bills it had already received, the supplier can usually argue the resulting shortfall isn't its fault, and pursue the older charges in full. 

Tampering with a meter or stealing energy 

The most serious exception covers deliberate interference with the meter, or using energy without a valid supply arrangement. Where there's evidence of tampering or theft, none of the standard back billing protections apply, and suppliers can pursue the full historic amount alongside any other action available to them. 

Outside these three scenarios, you won't be penalised simply for not providing meter readings. That responsibility sits mainly with the supplier, especially once a smart meter is in place to handle it automatically. 

How to check if a back bill is valid 

Before you pay, or dispute, a back bill, it's worth working through a short checklist to establish whether the charge is one that Ofgem's rules actually protect you from. 

Confirm your business qualifies as a microbusiness 

Start here, because the formal 12-month cap only applies if you meet Ofgem's microbusiness definition. Check your latest annual energy consumption in kWh against the thresholds above, or check your employee numbers and turnover. If you're not sure of your usage, your supplier or your latest bill should have this figure. 

Check the date the charge relates to 

Work out exactly which period the back bill covers, and compare it against the date the corrected invoice was issued. If any part of the charge relates to energy used more than 12 months before that invoice date, that part is a candidate for challenge, assuming the delay wasn't your fault. 

Establish whether the delay was the supplier's fault 

This is usually the deciding factor. If you requested bills and never got them, sent in meter readings that were ignored, or were simply never set up correctly on the supplier's system, the fault sits with the supplier. If, on the other hand, you blocked access, ignored correspondence, or interfered with the meter, the exceptions above are likely to apply. 

What to do if you receive an energy back bill 

If you've worked through the checklist above and think some or all of a back bill falls outside Ofgem's back billing rules, don't ignore it, and don't just pay it in full by default. Here's how to approach a dispute, in order. 

Step 1 - Challenge the bill in writing 

Contact your supplier in writing (email is easiest, since it creates a record) setting out that you believe the charge breaches Ofgem's 12-month back billing rule. State the period in dispute, explain why you believe the delay was the supplier's fault, and ask for a corrected invoice. Keep copies of meter readings, previous correspondence, and the original back bill. 

Step 2 - Escalate to a formal complaint 

If your supplier rejects the challenge, or doesn't reply within a reasonable time, ask for the matter to be treated as a formal complaint. Every supplier has to have a complaints process, and putting your dispute through it formally starts the clock on your right to escalate further if it isn't resolved. 

Step 3 - Refer the dispute to the Energy Ombudsman 

If your complaint hasn't been resolved after eight weeks, or your supplier has issued a deadlock letter confirming it won't change its position, you can refer the dispute to the Energy Ombudsman. This service is free for microbusinesses and can order a supplier to correct a bill, write off charges that breach the back billing rules, and in some cases pay compensation for the inconvenience caused. 

How to avoid future back billing

The best protection against a shock catch-up bill is stopping the underlying estimate from ever drifting too far from your real usage. 

Submit regular meter readings 

If you don't have a smart meter yet, get into the habit of sending in readings every month, even if your supplier only bills quarterly. This keeps your account close to your actual consumption and cuts the chance of a large correction building up unnoticed. 

Consider a smart meter 

A smart meter sends readings to your supplier automatically, taking the guesswork out of billing almost entirely. As more businesses move onto smart meters, suppliers have less reason to fall back on estimates, and fewer catch-up bills should follow. 

Check your bills against your actual usage 

Even with a smart meter installed, it's worth periodically checking that your bill matches what the meter is actually recording, and that the account hasn't quietly reverted to estimates. Building this into a regular business energy audit makes it far easier to catch a billing error early, before it turns into a back bill. 

Ofgem back billing rules FAQs

Got more questions on back billing rules? Check out the answers to some of our most frequently asked questions.

What is back billing in UK energy? 

Back billing is when an energy supplier charges for energy that was used in the past but not billed correctly at the time. 

What is Ofgem’s 12-month back billing rule? 

The rule prevents suppliers from charging for energy used more than 12 months ago if the billing error was their responsibility. 

Does the 12-month rule apply to all businesses? 

Not all businesses. It applies mainly to microbusinesses that meet Ofgem’s size or energy usage thresholds. 

What qualifies as a microbusiness under Ofgem rules? 

A microbusiness is one with fewer than 10 employees, or low turnover, or energy use under set kWh limits. 

Can energy suppliers charge for more than 12 months? 

Yes, if the customer caused the billing delay, such as by denying meter access or ignoring communications. 

What is a catch-up bill in energy billing? 

A catch-up bill is a single invoice covering previously unbilled energy, often based on updated meter readings. 

How do I dispute an energy back bill? 

You should contact your supplier in writing, raise a formal complaint if needed, and escalate to the Energy Ombudsman if unresolved. 

How can businesses avoid back billing issues? 

Regular meter readings, using smart meters, and checking bills against actual usage help prevent large back bills.