One set of long accounts can contain two Corporation Tax return periods.
A Corporation Tax accounting period cannot exceed twelve months. Split the period correctly, apportion figures and control both return and payment records.
Why the split occurs
A company can prepare accounts covering more than twelve months in permitted circumstances, including some first accounts or a changed year end. A Corporation Tax accounting period cannot be longer than twelve months, so the accounts period may need two Company Tax Returns.
Create two controlled period records
For each Corporation Tax accounting period, record:
- Start and end date
- Allocated accounting profit or loss
- Tax adjustments and relief claims
- Applicable rates and limits
- CT600 and supplementary pages
- Payment deadline, filing status and submission reference
Apportionment needs tax judgement
Some amounts are time-apportioned while others follow the underlying transaction, statutory rule or claim. Do not assume every figure is divided by days. Document the basis used and review how thresholds, associated companies, losses and reliefs apply to each period.
Reconcile both returns to the accounts
The two computations should reconcile back to the full accounts period without duplicated or omitted amounts. Cross-check the combined accounting result, tax adjustments, payments and liabilities before authorising either submission.
Common control failures
Long periods add opportunities for mismatch.
- Using the accounts dates as one CT600 period
- Duplicating a balance or adjustment in both returns
- Applying the wrong rate or limit to one period
- Recording only one payment deadline
- Retaining only one of the two submission responses
Where professional judgement is needed
This guide explains a filing workflow, not the accounting treatment, tax position or legal duties of a particular company. Confirm the applicable accounting framework, reliefs, disclosures and filing obligations against current official guidance and, where needed, a qualified accountant or tax adviser.
FAQ
Can a Corporation Tax accounting period exceed twelve months?
No. A longer accounts period is split into Corporation Tax accounting periods of no more than twelve months.
Will a fifteen-month first set of accounts need two returns?
It commonly will, because the Corporation Tax periods cannot exceed twelve months.
Are all figures apportioned by days?
No. The correct basis depends on the item and tax rules. Some figures follow transactions or specific statutory rules.
Are there two payment deadlines?
There can be separate payment obligations for the two Corporation Tax accounting periods. Check the dates for the particular company.
Official sources
Checked on 2026-08-11. Official guidance takes priority if rules change.