How long can an energy company backdate a bill in the UK?
This page exists for the direct search query people actually use. The real answer depends on the billed period, the reading history and whether the supplier had what it needed to bill accurately earlier.
The short answer
You should not accept “how long can they backdate a bill?” as a single yes or no question. First work out whether the supplier is correcting a recent catch-up issue or trying to recover usage from much older periods without having billed accurately when it should have done.
The 12 month back-billing protections are the key context for many household energy cases, but the facts still matter: the reading history, the billed period and why accurate billing did not happen earlier.
Use these pages too
Questions to ask in writing
- What exact dates does the charge cover?
- Which readings were used to build that balance?
- Why was accurate billing not issued earlier?
- Has the supplier assessed whether any part of the charge is outside the usual back-billing protections?
Official and reference sources
Frequently asked questions
Does every old-looking energy bill break the rules?
No. Some statements are recent catch-up corrections rather than improper recovery of very old usage.
What matters most in a backdated bill complaint?
The billed period, the reading history and the supplier’s written explanation of why accurate billing did not happen earlier.
Should I use this page or the main back-billing guide?
Use this page for the direct query and then move to the main back-billing guide for the fuller context.
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.
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.
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.
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.
Frequently asked questions
Is the answer simply twelve months?
Twelve months is the answer in the ordinary case, where the supplier failed to bill you accurately and you did nothing to prevent it. Outside that ordinary case — blocked access, ignored reading requests — there is no fixed limit, which is why the supplier's evidence matters more than the number.
Does the limit apply to a final bill after I move out?
The same 12-month principle applies to charges for energy used more than a year before the bill date. Closing bills that arrive very late are a common back-billing scenario; ask for the closing reading, the date it was taken and who supplied it.
What about debt already passed to a collection agency?
Raise the complaint with the supplier, not the agency, and tell both in writing that the balance is disputed under the back-billing rules. See how long an energy company can chase a debt.