Energy Back Billing Rules: 12-Month Rule, Exceptions and What to Ask
Back billing is not the same as “my bill is huge”. First identify whether the supplier is recovering old charges, correcting estimates or sending a normal catch-up bill.
Use together
The short answer
Back-billing rules usually protect customers from being charged for energy used more than 12 months ago when the supplier failed to bill correctly and the customer did not obstruct billing. But many large bills are actually catch-up bills based on previous estimates. You need to separate those two before complaining.
Rule and exception matrix
| Scenario | Likely issue | Best next step |
|---|---|---|
| Supplier is billing usage from more than 12 months ago | Possible back-billing protection | Ask them to identify old charges and the rule they rely on. |
| Previous bills were estimated and now actual read corrected them | May be catch-up rather than protected back billing | Check reading history and whether statements were sent. |
| You did not receive accurate bills for over a year | Strong back-billing review trigger | Use the not-billed-for-over-a-year page and template. |
| Meter access or readings were blocked | Protection may be weaker | Check what evidence the supplier has and whether you cooperated. |
| Supplier already billed the amount before | May not be new back billing | Ask for statement history and balance breakdown. |
What to ask the supplier
Which period is old?
Ask them to separate charges by supply period.
Which readings changed?
Get estimated and actual reading history.
What rule allows the charge?
Ask them to explain any exception they rely on.
What amount is disputed?
Separate undisputed recent use from disputed old use.
Focused back-billing question
Please also explain whether you consider those charges protected by the back-billing rules and, if not, which exception you rely on.
Until this is explained, I dispute the older portion of the balance and ask that collection activity on that portion is paused.
The rule itself, in one paragraph
Standard Licence Condition 21BA is the back-billing rule for domestic customers. It says a supplier must not charge you for gas or electricity used more than 12 months before the date of the bill, where the supplier is the reason you were not billed accurately during that period. It has applied to every licensed supplier in Great Britain since 1 May 2018. Microbusinesses get the same protection under SLC 7A.
Two things in that sentence do most of the work, and most complaints are lost on them:
- “12 months before the date of the bill.” The clock runs backwards from the bill, not from when you noticed, not from when the meter was last read, and not from when you first complained. A bill dated 3 September 2026 cannot properly charge you for energy used before 3 September 2025 if the supplier was at fault.
- “Where the supplier is the reason.” The protection is about supplier failure. If the supplier can show you obstructed accurate billing — refused meter access, ignored repeated reading requests, or behaved in a way the rule calls manifestly unreasonable — the protection can fall away for that period.
Source: Ofgem, Modification of the electricity and gas supply licences to introduce rules on backbilling, in force 1 May 2018. Always check the current licence text before quoting a condition number to a supplier — conditions are amended.
A worked example with real numbers
Abstract advice loses arguments. Here is the arithmetic a supplier has to be able to reproduce, using the Ofgem price cap rates for 1 July to 30 September 2026 (electricity 26.11p per kWh plus a 57.19p daily standing charge).
| Period on the bill | Units charged | At 26.11p/kWh | Standing charge | Line total |
|---|---|---|---|---|
| Apr 2024 – Mar 2025 older than 12 months | 2,900 kWh | £757.19 | 365 × 57.19p = £208.74 | £965.93 |
| Apr 2025 – Mar 2026 | 2,750 kWh | £718.03 | 365 × 57.19p = £208.74 | £926.77 |
| Apr 2026 – Aug 2026 | 950 kWh | £248.05 | 153 × 57.19p = £87.50 | £335.55 |
On a bill dated August 2026, the first row is the one that matters. It is roughly £966 of a £2,228 balance, it sits outside the 12-month window, and if the supplier failed to bill accurately during it, that line should come off. The other two rows are almost certainly payable — and saying so in writing is what makes the rest of the letter credible.
Why the standing charge line matters. People argue about units and forget that a full year of standing charge at 57.19p a day is £208.74 on electricity alone, before a single kWh. If a protected period is removed, its standing charges go with it. Ask for that explicitly, because it is frequently left on the bill.
Rates shown are the Ofgem cap averages for direct debit customers in England, Scotland and Wales, including VAT. Your region and payment method change them. Use the kWh to cost calculator with the rates printed on your own bill.
When the protection does not apply
Suppliers do sometimes have a real answer. It is worth knowing which ones are legitimate, because arguing against a valid exception wastes the eight weeks you need before you can escalate.
| What the supplier says | Does it hold up? | What to ask for |
|---|---|---|
| “You blocked access to the meter.” | Potentially valid. This is the main exception in the rule. | Dates of every access attempt, the letters or texts sent, and what response was recorded. |
| “You never gave us readings.” | Only if they asked and you did not respond. Silence from the supplier is their failure, not yours. | The reading-request history, and your own submitted readings from the app or account. |
| “This is a catch-up bill, not a back bill.” | Often true and often the real answer. | A period-by-period breakdown, so you can see which side of the 12-month line each charge sits on. |
| “The rule does not apply because you changed supplier.” | Weak. The obligation follows the supplier that failed to bill. | Which licensed entity billed each period, and the final statement from the losing supplier. |
| “There was a meter fault, so we could not bill.” | A fault is normally the supplier's problem to detect and fix. | When the fault was first flagged in their system and what they did about it. |
| “It was a billing system migration.” | Not an exception. An internal IT project is supplier fault. | Written confirmation that the delay was caused by their systems. |
Notice the pattern: almost every valid exception depends on something the supplier must be able to evidence. Asking for that evidence, in writing, is the whole move. A supplier that cannot produce a record of asking you for readings has effectively conceded the point.
Five things that sink these complaints
Disputing the whole balance
If you refuse to pay anything, the argument becomes about your payment behaviour instead of their billing failure. Name the undisputed amount and keep paying it.
Arguing on the phone
Phone notes are the supplier's version of events. The Ombudsman reads documents. Every substantive point goes in writing.
Calling it unfair rather than unbilled
“This is unaffordable” is a payment-plan conversation. “You did not bill me for this period and the rule prevents you recovering it” is a back-billing conversation. They have different outcomes.
Missing the standing charges
Removing a protected period should remove its daily standing charges too. On a two-fuel account that is over £300 a year.
Escalating too early
The Ombudsman will send you back if you have not given the supplier eight weeks or received a deadlock letter. That wastes a month.
What works instead
A dated timeline, a numbered list of requests, a named undisputed figure, and a clear statement that you will escalate on a specific date. That combination gets escalated internally rather than parked.
The letter, written out in full
Copy, fill in the square brackets, send by email
Numbering the requests matters more than the tone. A numbered list is harder to answer with a paragraph of general reassurance, and if it goes to the Ombudsman, it shows exactly which questions the supplier declined to answer.
What happens after you send the letter
Day 0 — written complaint
Send it by email or the supplier's complaint form so there is a timestamp. Ask for a complaint reference. Keep paying the undisputed part.
By day 56 — eight weeks
Either they resolve it, or you can take it to the Energy Ombudsman. A deadlock or “final response” letter unlocks that door sooner.
Then 28 days to implement
If the Ombudsman upholds the complaint, the supplier has 28 days to actually do what was decided. The decision binds the supplier, not you.
Confirmed for the near future: eight weeks becomes six
On 17 June 2026 the government published its response to the Fairer, faster redress in the energy market consultation and confirmed two changes: the wait before you can escalate drops from 8 weeks to 6 weeks, and the Ombudsman's own window for issuing a decision drops from 6 weeks to 4 weeks. Redress schemes will also get the power to penalise suppliers who fail to implement a decision on time.
None of this is in force yet. The response says the changes will be made “as soon as reasonably possible and certainly no later than Royal Assent for the Energy Independence Bill”. Until then, plan around eight weeks — but if your complaint is running into late 2026, check the current position before you assume you have to keep waiting.
Frequently asked questions
Is every catch-up bill back billing?
No. A catch-up bill can happen when estimates are replaced by actual readings. Back billing is specifically about older unbilled or incorrectly billed usage.
Can standing charges be included in back billing?
Back-billing issues can involve both usage and standing charges if they relate to the old period. Ask the supplier to break down the amount.
Should I ignore the bill while disputing it?
No. Ask what undisputed amount should be paid and keep the disputed older portion separate in writing.
Does the 12 months run from the bill date or the meter reading date?
From the date printed on the bill. A reading taken in June and billed in September is measured against the September date, which works in your favour.
What if I switched supplier during the period?
The obligation sits with the supplier that failed to bill accurately. Ask each supplier for the periods it billed and its final statement, then send the letter to whichever one is recovering the old charges.
Does the rule cover standing charges as well as units?
Yes. If a period is protected, the daily standing charges for that period go with it. On a dual-fuel account that is over £300 a year at current cap rates, so it is worth stating explicitly.
What if the supplier says it is a catch-up bill, not a back bill?
Ask for the balance broken down by supply period. That single document settles it: charges inside the last 12 months are a catch-up conversation, charges outside it are a back-billing one, and one bill can contain both.
Can they keep chasing the debt while I dispute it?
Ask in writing for collection activity on the disputed portion to be paused while the complaint is open, and keep paying the undisputed amount. Most suppliers will agree, and a refusal is itself worth putting to the Ombudsman.
Official sources used for this page
BillDecoded translates official process and billing information into practical checks. It is not affiliated with the Ombudsman, Ofgem, Citizens Advice, Which? or any supplier.