Corporation Tax Deadline Calculator: UK Dates 2026/27

Corporation Tax deadlines do not all fall on the same date. A UK limited company may need to file annual accounts with Companies House, pay Corporation Tax to HMRC and submit a Company Tax Return on three different deadlines.

This separation catches many new directors by surprise. The tax payment is normally due before the Company Tax Return, while the Companies House accounts deadline is calculated under a different set of rules.

This guide explains the main Corporation Tax and company filing deadlines, how to calculate them and what can happen if a company files or pays late.

Quick Corporation Tax deadline calculator

To estimate the standard Corporation Tax payment deadline, take the final day of the company’s Corporation Tax accounting period, add 9 months, then add 1 day.

• Accounting period ends 31 March 2026: payment is normally due 1 January 2027.
• Accounting period ends 30 June 2026: payment is normally due 1 April 2027.
• Accounting period ends 31 December 2026: payment is normally due 1 October 2027.

The Company Tax Return (CT600) is normally due 12 months after the accounting period ends. Companies House accounts usually have a separate deadline. These examples cover the standard rule; large companies, unusual accounting periods and HMRC notices can change the position.

Corporation Tax deadlines at a glance

These are general deadlines for many private companies. Large companies, companies with unusual accounting periods and businesses that receive a specific notice from HMRC may have different obligations.

Why are there several company deadlines?

Companies House and HMRC perform different roles. Companies House maintains the public register of companies, while HMRC administers Corporation Tax.

Your statutory accounts are sent to Companies House. A Company Tax Return, normally including the tax computation and accounts in the required electronic format, is sent to HMRC. Corporation Tax itself is paid separately.

Completing one obligation does not automatically complete the others. Filing accounts at Companies House does not mean the Company Tax Return has been submitted, and submitting a return does not mean the tax has been paid.

Corporation Tax payment deadline

For a company with taxable profits of up to the relevant large-company threshold, Corporation Tax is usually due 9 months and 1 day after the end of the accounting period.

For example, if the Corporation Tax accounting period ends on 31 March 2026, the normal payment deadline is 1 January 2027. If the accounting period ends on 31 December 2026, the normal payment deadline is 1 October 2027.

The payment deadline arrives three months before the standard Company Tax Return filing deadline. This means the company may need to calculate its tax liability before the final date for submitting the return.

Company Tax Return filing deadline

A Company Tax Return is normally due 12 months after the end of the accounting period it covers. A company with an accounting period ending on 31 March 2026 would therefore usually need to file its return by 31 March 2027.

The return includes more than a copy of the statutory accounts. It normally contains the CT600 form, the company’s accounts and tax computations showing how the taxable profit and Corporation Tax liability were calculated.

Companies should use suitable filing software and allow time to review the return before submission. Saving a return in accounting software is not the same as successfully sending it to HMRC.

Companies House annual accounts deadline

Most established private companies must file annual accounts with Companies House within 9 months of the end of their financial year.

If the company’s financial year ends on 31 March 2026, its annual accounts will normally be due at Companies House by 31 December 2026. This is separate from the 1 January 2027 Corporation Tax payment deadline and the 31 March 2027 Company Tax Return deadline.

The dates may appear close together, but they are not interchangeable. Directors should check the exact due dates shown on the company record and in HMRC’s business tax account.

First accounts for a new company

The first accounting period often needs extra attention. A private company’s first accounts are usually due 21 months after the date of incorporation, but the Corporation Tax position may not follow the same period.

A Corporation Tax accounting period cannot normally be longer than 12 months. If the first statutory accounts cover more than 12 months, two Company Tax Returns may be needed. The company may also have two Corporation Tax payment deadlines.

For example, a company may prepare first accounts covering slightly more than one year to reach its chosen month-end. The statutory accounts can cover that longer period, while the tax reporting is split into a maximum 12-month period and a shorter second period.

When does a Corporation Tax accounting period begin?

A Corporation Tax accounting period usually begins when the company starts business activity and becomes active for Corporation Tax. Incorporating a company does not always mean that trading starts on the same day.

Activity may include selling goods or services, providing services, earning interest or managing investments. A company that has not started activity may be dormant for Corporation Tax purposes, although it can still have Companies House responsibilities.

Once trading begins, check HMRC and Companies House record-keeping requirements. The company’s accounting records should start from the correct date.

Dormant companies and filing responsibilities

A dormant company may not owe Corporation Tax and may not need to submit a Company Tax Return unless HMRC asks for one. However, dormant companies generally still need to file appropriate accounts with Companies House and complete other company-law obligations.

If HMRC has issued a notice to deliver a Company Tax Return, do not ignore it merely because the company was dormant. Confirm the position with HMRC and follow the required process.

A company that resumes trading should update HMRC and begin keeping complete accounting records from the date activity restarts.

Large companies and instalment payments

The standard 9-month-and-1-day payment rule does not apply to every company. Companies with taxable profits above the large-company thresholds may need to pay Corporation Tax by instalments, with some payments falling before the accounting period ends.

The thresholds can be affected by the number of associated companies and the length of the accounting period. A group or a business with connected companies should not assume that the headline profit threshold applies without adjustment.

If profits are approaching the relevant level, calculate the position early. Discovering an instalment requirement after a payment date has passed can create interest charges and cash-flow pressure.

What records does a limited company need?

Accurate Corporation Tax reporting begins with complete bookkeeping. The company should retain records that support its income, expenses, assets and liabilities. Read our guide to UK bookkeeping service costs and review our bookkeeping packages.

Common records include:

• Sales invoices and other income records
• Purchase invoices and expense receipts
• Business bank and credit-card statements
• Payroll reports and employer records
• VAT returns and supporting calculations
• Loan agreements and interest statements
• Asset purchase and disposal records
• Director’s loan account transactions
• Dividend paperwork and shareholder records
• Details of grants, reliefs and tax losses

Personal and company money must be kept distinct. Transactions involving directors or shareholders should be recorded correctly rather than being treated automatically as ordinary business expenses.

Allowable expenses and tax adjustments

The profit shown in the statutory accounts is not always the same as taxable profit. The Corporation Tax computation adjusts the accounting result for items that are treated differently under tax rules.

Some expenses may be disallowed for Corporation Tax, while capital allowances may be available on qualifying assets. Other adjustments can involve depreciation, entertaining, provisions, losses, research and development claims or transactions with connected parties.

Good bookkeeping makes these adjustments easier to identify, but tax treatment should still be reviewed rather than relying only on the category selected in the bookkeeping software.

What happens if Corporation Tax is paid late?

HMRC normally charges interest on late Corporation Tax payments. Interest can continue until the outstanding amount is paid.

Paying late is separate from filing late. A company can submit its return on time but still incur interest because the tax was not paid by the earlier payment deadline.

If the exact liability is not ready, obtain advice before the deadline. It may be appropriate to make a reasonable payment based on the available information and adjust it later, but the correct approach depends on the circumstances.

Company Tax Return late-filing penalties

HMRC can charge a penalty when the Company Tax Return is filed late. Under current rules, an initial fixed penalty can arise as soon as the return is late, followed by another fixed penalty after three months.

Further tax-related penalties can arise after six and twelve months. Repeatedly filing late can also increase the fixed penalties.

These HMRC penalties are separate from Companies House penalties for late statutory accounts. A company that misses both deadlines can therefore face consequences from both organisations.

Companies House late-accounts penalties

Companies House normally imposes an automatic civil penalty when accounts are delivered late. The penalty increases according to how long the accounts remain overdue, and the amount can be doubled if accounts are late in two consecutive financial years.

Directors are legally responsible for ensuring the accounts are prepared and delivered on time, even when an accountant helps with the work.

If an event outside the company’s control may prevent filing, an application to extend the accounts deadline should normally be made before the existing deadline. An extension should not be assumed.

A worked deadline example

Consider an established private company with a 31 March 2026 year end and no special payment rules.

• Companies House annual accounts: normally due 31 December 2026
• Corporation Tax payment: normally due 1 January 2027
• Company Tax Return: normally due 31 March 2027

This example shows why a company should not wait for the tax-return deadline before calculating its liability. The tax is normally due well before the return.

How to avoid missing company deadlines

1. Confirm the financial year end and Corporation Tax accounting-period dates.
2. Check the exact deadlines with Companies House and HMRC.
3. Maintain bookkeeping throughout the year.
4. Reconcile bank, loan, payroll and VAT balances regularly.
5. Keep director’s loan and dividend records up to date.
6. Provide year-end information promptly.
7. Review the expected Corporation Tax bill before the payment deadline.
8. Arrange cleared payment using the correct reference.
9. Submit both the accounts and Company Tax Return.
10. Retain acceptance confirmations and final documents.

Set internal target dates several weeks before the statutory deadlines. This provides time to answer queries, correct records and plan the payment without last-minute pressure.

Support with Corporation Tax deadlines

Company deadlines are easier to manage when bookkeeping records are complete and provided to the appropriately authorised professional in good time. Regular reconciliations can reduce missing information and give directors a clearer view of business records.

Real Key Accountancy provides bookkeeping and related accountancy support within its authorised scope. Corporation Tax computations, Company Tax Returns, statutory accounts or tax advice that fall outside the agreed scope must be completed by a suitably qualified and authorised professional.

For help organising the bookkeeping records needed ahead of company deadlines, contact Real Key Accountancy.

Frequently asked questions

Is Corporation Tax due when the Company Tax Return is filed?

No. For many companies, the tax is due 9 months and 1 day after the accounting period ends, while the return is due 12 months after the period ends.

Are Companies House accounts and a Company Tax Return the same?

No. They are separate filings made to different organisations, although the underlying accounts information is related.

Can a company file early?

Yes. Once the accounts and tax calculations are complete, the required filings can usually be made before their deadlines.

What if the company made a loss?

A loss may mean no Corporation Tax payment is due, but filing obligations can still apply and the loss should be calculated and reported correctly.

Who is responsible for meeting the deadlines?

The company’s directors remain responsible for ensuring its legal and tax obligations are completed, even when professional advisers assist.

Reviewed September 2026. This article provides general information and does not constitute personalised tax or legal advice. Rules and company circumstances vary, so verify deadlines with HMRC and Companies House and obtain advice from an appropriately authorised professional.