Free household bill check

Back-billing calculator: check the 12-month date window

Find which consumption days sit outside the usual 12-month window, then check the billing history and exceptions before challenging a catch-up bill.

Reviewed 19 October 2026 · BillDecoded editorial team · Methods and limitations

Find the 12-month back-billing cut-off

Use the dates for the newly recovered charges. Both consumption dates below are included. Nothing you enter is uploaded.

First date the supplier sought payment for these new charges

Usually the first bill or demand for the shortfall. A later copy or reminder does not automatically create a new starting point.

First consumption day covered

Last consumption day covered (included)

Was this same amount accurately billed or stated before?

An old unpaid accurate bill is different from a newly recovered shortfall.

Did your conduct prevent accurate billing?

For example, blocking meter access. Missing a reading or receiving estimates is not automatically the same as unreasonable obstruction.

Calendar 12-month cut-off

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Consumption days before cut-off

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Consumption days on/after cut-off

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Enter the dates and check the two evidence questions.

Worked example: an October 2026 catch-up bill

Suppose new recovery action is dated 19 October 2026 and the newly billed consumption runs from 19 April 2025 to 18 October 2026 inclusive. The calendar cut-off is 19 October 2025.

Consumption interval	Calendar days	What to examine
19 April–18 October 2025	183	Older than the date window; check previous billing and exceptions.
19 October 2025–18 October 2026	365	Inside the date window; readings, rates and liability still need checking.

These 548 days are not 548 equal units of energy. Gas use can be seasonal, rates can change and earlier payments may cover different charges. Do not multiply the old-day percentage by the total invoice and call it a guaranteed write-off. Ask for actual consumption and charge lines on each side of the cut-off.

When the date split is not enough

Find the earlier bills and statements for the same amount, not just the latest account balance.
Separate new underbilled consumption from accurate bills left unpaid.
Ask the supplier to identify any customer-conduct exception and the evidence relied on.
Compare readings, tariff periods, daily standing charges, payments and credits.

Ofgem describes protection for some older unbilled or underbilled charges and exceptions. Read the full back-billing rule and exceptions before using a date result in a complaint. A catch-up bill based on estimates can still require this review.

Ask for a charge-by-charge explanation

Please identify the first recovery date for each newly added shortfall in [bill/reference]. The consumption period is [dates]. Please separate charges before and on/after [12-month cut-off], showing readings, actual usage, rates, standing charges, payments and credits. Please identify the earlier accurate bill or statement for any amount you say was already billed, and the evidence for any exception to the back-billing protection. Please explain whether and how SLC 21BA was applied. I am asking for a reconciliation; this date calculation is not a claim that every older balance disappears.

Full back-billing complaint template · Estimated readings · Split rate-period charges · Complaint timing.

Sources and scope

The checker uses calendar dates, not 365 days, and includes both consumption endpoints. For a 29 February recovery date, the previous-year cut-off is 28 February. If a particular day's legal treatment is disputed, ask the supplier or adviser to confirm it. The tool covers the GB household rule from May 2018; it does not assess historic rules, business status, debt limitation periods, court outcomes or refund entitlement. General information only.

Frequently asked questions

Does a date before the cut-off mean I owe nothing?

No. Previous accurate bills or statements and relevant exceptions still matter. The result separates dates; it does not decide liability.

Does an estimated bill rule out back-billing protection?

Not automatically. Check the newly recovered shortfall and the earlier billing record against the rule and exceptions.

Can I divide the bill by days to find a refund?

No. Usage, rates and payments may vary across the period. Request the actual charges around the cut-off.

Why use a calendar year rather than 365 days?

The check is for a 12-month window. Calendar years can include a leap day; the tool states its boundary convention.