Back billing UK rules — energy companies can charge you for past energy use but only up to 12 months in most cases.
What Is Back-Billing?
Back-billing is when your energy supplier charges you for energy you used in the past that wasn’t billed at the time. It usually happens because:
- Your smart meter wasn’t sending readings properly
- Your supplier failed to issue accurate bills
- Estimated bills significantly undercharged you over a long period
- A meter exchange or supplier switch caused a billing gap
The result is a large unexpected charge appearing on your bill — sometimes covering months or even years of usage. This is one of the most distressing billing problems customers face.
The 12 Month Back-Billing Rule
Under Ofgem’s rules, energy suppliers cannot back-bill domestic customers for energy used more than 12 months before the bill was issued — as long as the customer was not at fault for the billing failure.
This means if your supplier failed to bill you correctly for 2 years, they can only recover charges for the most recent 12 months. The rest must be written off.
The key condition: The protection applies where the supplier was at fault — for example, failing to read your meter, failing to act on readings you provided, or issuing inaccurate estimated bills over a long period.
If you deliberately withheld access to your meter or provided false readings, the protection may not apply.
When Does the 12 Month Rule Apply?
The back-billing protection applies when:
- Your supplier failed to bill you accurately through no fault of your own
- You were on estimated bills despite having a smart meter that should have been sending readings
- A billing error on the supplier’s side caused the underbilling
- A meter exchange or switch caused a gap in billing that the supplier failed to address
It may not apply if:
- You refused access for meter readings
- You knew you were being undercharged and didn’t tell your supplier
- You provided inaccurate meter readings
Smart Meters and Back-Billing
Smart meters make back-billing disputes more complex — and more common.
If your smart meter stopped sending readings after a supplier switch or due to a signal problem, your supplier may have continued issuing estimated bills based on old data. When the readings eventually come through, the gap becomes a large backdated charge.
In most cases — if your smart meter stopped working through no fault of your own — you have a strong argument that the 12 month back-billing protection applies. Your supplier had the tools to monitor your meter’s connection status. If they failed to act on a communication fault, the billing failure is on them.
→ Smart meter signal problems — what your supplier must do
How to Challenge a Backdated Bill
If you’ve received a backdated bill you believe is unfair or exceeds the 12 month limit — follow these steps:
Step 1 — Don’t pay it immediately. You have the right to challenge the bill before paying. Paying it without challenge may be seen as acceptance.
Step 2 — Write to your supplier formally. Reference the Ofgem back-billing protection. State clearly that you believe the charges exceed the 12 month limit and request a full breakdown of the billing period.
Step 3 — Request a breakdown. Ask your supplier to provide a detailed breakdown showing exactly which period the charges relate to and why the billing failure occurred.
Step 4 — Raise a formal complaint. If your supplier refuses to apply the 12 month protection or won’t provide a satisfactory explanation — raise a formal complaint in writing.
Step 5 — Escalate if needed. If your complaint isn’t resolved within 8 weeks, you can take it to the Energy Ombudsman for free. The Ombudsman can order your supplier to write off charges that breach the back-billing rules.
→ Generate your formal complaint letter — free
→ How the Energy Ombudsman works
What to Say to Your Supplier
Use this wording when contacting your supplier:
“I am writing to formally dispute the backdated charges on my account. Under Ofgem’s back-billing rules, energy suppliers cannot charge domestic customers for energy used more than 12 months before the bill was issued where the supplier was at fault for the billing failure. I believe the charges on my account exceed this limit and request that you write off any charges relating to energy used more than 12 months ago. Please provide a full breakdown of the billing period and confirm your position in writing within 5 working days.”
If Your Supplier Has Already Added It to a Payment Plan
Some suppliers add disputed backdated charges to a repayment plan without properly explaining the back-billing rules. If this has happened to you — raise a formal complaint immediately. You should not be repaying charges that breach the 12 month rule.
Your Rights Under Ofgem’s 2026 Rules
Back-billing disputes are covered by your broader rights under Ofgem’s framework. Once you formally report a billing dispute, your supplier must provide a resolution plan within 5 working days under GSOP 3. Failure to do so triggers £40 automatic compensation.
→ Your full rights under Ofgem’s 2026 rules
The Bottom Line
A large backdated bill does not have to be paid in full. The 12 month back-billing protection exists specifically to prevent suppliers from recovering years of underbilling from customers who had no way of knowing they were being undercharged.
Challenge it. In writing. Citing the rule. Your supplier knows it applies.
→ Generate your complaint letter now — free
Written by a qualified UK smart meter installer. Independent advice — not affiliated with any energy supplier. smartmeterhelp.co.uk