Changing your company year end: accounts periods and filing traps

Separate the dates before making a change

The accounting reference date sets the company’s annual accounts cycle at Companies House. The statutory accounts period, the accounts filing deadline and HMRC’s Corporation Tax accounting periods are related but not interchangeable. A first set of accounts can cover more than 12 months; a Corporation Tax accounting period cannot.

Changing a year end may help align with a parent, trading season or management reporting. It can also complicate tax returns, comparative figures and budgets. Ask your accountant to write out the old and proposed periods and deadlines before filing. Do not approve the change based on a single calendar date or an assumption that every deadline automatically moves by the same number of months.

Understand a shortened accounting period

A company can generally shorten an eligible period by at least one day and can do so more often than it can lengthen it. The change still needs a valid filing and must be made before the relevant accounts are overdue. Shortening is not merely an internal decision to close the books early.

A shortened period can produce a different accounts filing deadline under the statutory rules, including the relevant protection for the time following notice of the change. Have the accountant confirm the specific resulting deadline from official guidance. Tax calculations may also use apportioned allowances or thresholds, and comparative accounts need context where periods differ.

• Check which current or immediately previous period is eligible.
• Confirm the current accounts are not overdue.
• Model the accounts deadline before submitting the change.
• Assess short-period tax allowances and computations.
• Update budgets and comparisons to reflect unequal period lengths.

Review extension limits and exceptions

A period can normally be extended to no more than 18 months. Extension is usually allowed only once in five years, with statutory exceptions such as qualifying alignment with another group company, administration or permission. Those exceptions need to fit the real facts; they are not generic ways to delay accounts repeatedly.

A filing extension already granted for accounts may be cancelled by a year-end change. If the new deadline has passed, a penalty may result. Accounts already overdue cannot be rescued by changing the accounting reference date for that period. Where more time is needed because of an exceptional event, investigate the separate official accounts-extension process promptly rather than improvising a date change.

Submit AA01 or use the supported online service

The Companies House process identifies the company, the period being changed and the new date. Use form AA01 or the relevant online service and complete any extension grounds correctly. Keep the approval and submission evidence, then check the updated register and filing deadline. A filed application is not confirmation that an invalid extension was accepted.

Tell the accountant exactly what was registered. If work has already begun on accounts for the old period, reconcile the cut-off and scope before proceeding. Update the internal calendar, bank covenant schedules and reporting commitments where the new date matters. A lender or investor may require approval for a financial year-end change under its agreement.

1. 1

   Ask the accountant to model old and proposed periods.

2. 2

   Check eligibility, previous extensions and overdue status.

3. 3

   Obtain any internal, lender or investor approval.

4. 4

   File the appropriate Companies House change.

5. 5

   Verify the registered date and accounts deadline.

6. 6

   Update HMRC periods, accounts work and every relevant calendar.

Deal separately with Corporation Tax periods

Notify HMRC of the change and establish the correct Corporation Tax periods and return requirements. A 15-month statutory accounts period can require two Company Tax Returns, often one for 12 months and one for the remaining three months. The tax computations need appropriate allocations; do not simply treat the whole accounts period as a single tax year.

Tax payment and return deadlines should be calculated for each actual tax accounting period. Larger or qualifying companies may be subject to instalment rules. Allowances, losses and associated-company thresholds can require period-sensitive treatment. Your accountant needs the date trading began as well as the statutory year end, especially for newly formed companies.

Worth knowing: A Companies House year-end update does not replace the need to establish the company’s separate HMRC accounting periods.

Worked scenario: aligning with a parent company

Illustrative scenario: a subsidiary has a 31 December year end and wants to align with a parent’s 31 March reporting date. Its advisers check whether extending the current period to 15 months is permitted, review the relevant group-alignment exception and calculate the Companies House deadline before filing. They also consider lender reporting requirements.

The subsidiary’s accountant prepares the 15-month statutory accounts but establishes separate tax periods because Corporation Tax periods cannot exceed 12 months. The directors receive a calendar showing accounts filing, both tax returns and payment dates. This is more useful than a reminder saying only “new year end: 31 March”.

Evaluate a year-end change with the accountant first

A company may want a year end that aligns with a group, a seasonal cycle or its accountant’s workflow. The directors begin by listing the existing accounting reference date, current accounts period, filing deadline and Corporation Tax periods. They explain the commercial reason for the proposed change and check the official limits on shortening or extending the period. A change cannot be used as a casual assumption that overdue accounts receive more time. The accountant models the statutory filing result before the company submits the change.

Companies House accounts periods and Corporation Tax accounting periods are related but not identical. A Corporation Tax accounting period cannot simply become an eighteen-month tax period because the statutory accounts are extended. The accountant identifies whether two tax returns are needed, how income and deductions are allocated and when payments fall due. Payroll tax years and VAT periods also do not automatically follow the new company year end. The directors maintain separate dates in the calendar and label any official override obtained from the actual register or HMRC record.

The company checks eligibility and restrictions for the proposed change, including the maximum length and rules on repeated extensions. It confirms whether accounts are already overdue and whether a filing route is available. The directors keep the decision and accepted submission, then read back the new date and deadline from the official record. They do not rely solely on an internal spreadsheet calculation. Where lenders, investors or a parent company expect accounts on a particular date, they coordinate those reporting duties because a Companies House change does not automatically amend private contracts.

Bookkeeping then needs a clear cutoff and asset, stock, debtor and creditor records for the revised period. Budgets and management reports should explain the longer or shorter period so comparisons are not misleading. The company reviews annual allowances, thresholds and period-dependent tax computations with the accountant. The first revised return includes a reconciliation showing how periods fit together. Subsequent reminders are updated only after the official change is accepted. This avoids the common error of altering the calendar while leaving the return preparation and tax-payment plan on the old assumptions.

Keep comparison and deadline records clear

When reporting performance, distinguish genuine growth from a longer reporting period. A 15-month revenue total should not be compared with a 12-month total without explanation. Budgets, payroll summaries, VAT data and internal dashboards may run on different cycles; label them so directors do not draw conclusions from mismatched periods.

Retain the reasons for the change, approval evidence, Companies House acceptance and HMRC correspondence. Verify that reminder services use the new dates and that any official-date override is clearly labelled in a planning tool. If a deadline seems inconsistent, resolve it against official records before relying on an estimated calendar.

Common questions

Official sources & further reading

This guide draws on the official guidance below. Rules, fees and individual circumstances can change; check the relevant source before acting.

• GOV.UK: Change your company year end
• Companies House: AA01
• GOV.UK: Corporation Tax accounting periods

General UK information, primarily for private companies limited by shares. This is not personalised legal, tax or financial advice. An accountant or solicitor can help apply the rules to your situation.