When Is Corporation Tax Due? UK Deadlines Explained

Corporation Tax deadlines cause more confusion than they should. The difficulty is not usually the headline rule itself; it is the way the payment deadline, Company Tax Return deadline, Companies House accounts deadline and accounting period all sit close together without being the same thing.

For a UK limited company, Corporation Tax is usually due 9 months and 1 day after the end of the company’s accounting period. The Company Tax Return is usually due later, 12 months after the end of that accounting period. Statutory accounts filed with Companies House have their own timetable. Missing the distinction between these deadlines is one of the most common causes of late payment, rushed filings and avoidable HMRC correspondence.

This guide explains how the UK Corporation Tax deadline works, how it differs from filing obligations, what changes in the first year of trading, and why bookkeeping discipline matters long before the tax payment date arrives.

The short answer: when Corporation Tax is normally due

For most UK limited companies, Corporation Tax must be paid to HMRC 9 months and 1 day after the end of the company’s accounting period for Corporation Tax.

If a company’s accounting period ends on 31 March 2025, the Corporation Tax payment deadline is normally 1 January 2026.

If the accounting period ends on 30 June 2025, the Corporation Tax payment deadline is normally 1 April 2026.

This is the payment deadline, not the filing deadline. The Corporation Tax return, usually submitted on form CT600 with supporting computations and accounts, is normally due 12 months after the end of the accounting period. Businesses that need more context on the return process may find this overview of Corporation Tax returns useful alongside HMRC’s own guidance.

That creates a practical problem: in many cases, the tax must be paid before the return is due. A company therefore needs reliable management information, reconciled bookkeeping and a reasonable tax calculation well before the final filing date.

Corporation Tax payment and filing are not the same deadline

HMRC separates the duty to pay Corporation Tax from the duty to file the Company Tax Return. This distinction matters because some directors assume that no payment is needed until the CT600 is submitted. That assumption can lead to interest charges even if the return itself is filed on time.

The two core deadlines are usually:

• Corporation Tax payment: 9 months and 1 day after the end of the accounting period.
• Company Tax Return filing: 12 months after the end of the accounting period.

For a company with a 31 March year end, the Corporation Tax payment deadline will normally fall on 1 January, while the CT600 filing deadline will normally fall on 31 March. The company has three additional months to file the return, but not three additional months to pay the tax.

This timing often catches owner-managed companies by surprise. The accounts may not feel “finished” by the payment deadline, especially if year-end adjustments, director loan account reviews, payroll reconciliations, VAT checks or CIS deductions are still being resolved. HMRC still expects the tax to be paid by the due date based on the best available calculation. Where the liability is unclear, broader Corporation Tax support can help directors understand the compliance sequence without confusing payment with filing.

How the accounting period drives the Corporation Tax due date

The Corporation Tax deadline is linked to the company’s accounting period, not automatically to the tax year ending 5 April. Limited companies choose or inherit an accounting reference date, commonly the last day of a month. The accounting period for Corporation Tax will usually follow the company’s financial year, but there are exceptions.

A company cannot have a Corporation Tax accounting period longer than 12 months. If the first set of accounts covers more than 12 months, the Corporation Tax return period is split. This is common for newly incorporated companies that prepare first accounts for a period longer than a year.

For example, a company incorporated on 10 May 2024 might prepare first accounts to 31 May 2025. That is longer than 12 months. For Corporation Tax purposes, HMRC may expect two returns: one covering the first 12 months and another covering the remaining short period. Each period can have its own payment and filing timetable.

This is one reason first-year compliance is often less straightforward than directors expect. The company may appear to have one Companies House accounts period, but more than one Corporation Tax accounting period.

Companies House deadlines add another layer

Corporation Tax deadlines sit alongside Companies House accounts deadlines, but they are not identical. Companies House is concerned with statutory accounts and company law filing obligations. HMRC is concerned with Corporation Tax returns, computations and payment.

For a private limited company, the first accounts are usually due at Companies House 21 months after incorporation. Later annual accounts are normally due 9 months after the company’s financial year end.

This creates a timing overlap. For established companies, the Companies House accounts deadline often falls around the same time as the Corporation Tax payment deadline. A company with a 31 March year end may have:

• Companies House accounts due: normally 31 December 2025;
• Corporation Tax payment due: normally 1 January 2026;
• Corporation Tax return due: normally 31 March 2026.

The closeness of these dates is not accidental in practice, but it can be misleading. Filing accounts at Companies House does not automatically mean the Corporation Tax return has been filed with HMRC. Paying Corporation Tax does not automatically mean accounts have been filed. Each obligation needs its own process and confirmation.

A practical example: 31 March year end

Take a trading company with a year end of 31 March 2025. Its usual Corporation Tax timetable would look like this:

• Accounting period ends: 31 March 2025.
• Companies House accounts due: 31 December 2025, assuming this is not the first accounts period.
• Corporation Tax payment due: 1 January 2026.
• Corporation Tax return due: 31 March 2026.

The operational lesson is simple but often ignored: by late December, the company should already have a reliable tax estimate. Waiting until March to calculate the tax may keep the filing deadline safe, but it does not protect the payment deadline.

Where bookkeeping is maintained throughout the year, the tax position can usually be estimated before the accounts are finalised. Where records are incomplete, the company may struggle to distinguish between actual profit, unpaid invoices, director drawings, VAT liabilities and cash that appears available but is already committed.

What changes for a newly formed company

New companies face extra confusion because incorporation, trading, accounts and tax registration do not always start on the same day.

A company may be incorporated at Companies House but not start trading immediately. Corporation Tax usually becomes relevant once the company starts business activity, such as trading, receiving income, selling goods or services, employing staff, or earning interest. HMRC should be told when the company becomes active, usually within three months of starting business activity.

The first year can involve:

• a Companies House accounting reference date based on incorporation;
• a trading start date that differs from the incorporation date;
• a first accounts period longer than 12 months;
• one or more Corporation Tax accounting periods;
• new payroll, VAT, CIS or bookkeeping processes being set up at the same time.

For a director managing a new company, the risk is not only missing a date. It is assuming all systems begin neatly together. They rarely do. A company might register for VAT part way through the year, run payroll before invoices become regular, or incur pre-trading costs before revenue starts. These details can affect records, deductions and the accuracy of early tax estimates.

Why the tax is due before the return is filed

Some directors find it counterintuitive that Corporation Tax is payable before the tax return deadline. From HMRC’s perspective, the company is expected to calculate and pay the tax based on its own records. The CT600 later confirms the position formally.

This makes Corporation Tax different from the way some individuals think about Self Assessment, where the tax return and payment deadline are closely associated. A limited company needs to treat Corporation Tax as a cashflow obligation arising from profit, not as an afterthought attached to the final submission.

If the payment made before the deadline is too low, HMRC may charge interest on the unpaid amount. If the company overpays, it may be able to obtain a repayment or offset, but overpayment also ties up cash unnecessarily. The aim is not guesswork; it is a credible estimate supported by current records.

The bookkeeping reality behind Corporation Tax deadlines

Corporation Tax problems often begin months before anyone logs into HMRC. Late tax payment is usually a symptom of poor visibility rather than a single administrative mistake.

Typical causes include unreconciled bank accounts, missing purchase invoices, sales recorded outside the accounting system, director expenses paid personally, payroll journals not posted, VAT control accounts not reviewed, and loan balances left unresolved until the year end. None of these issues may feel urgent during the year, but together they make the tax calculation unreliable.

For companies working in construction, CIS can add further complexity. Deductions suffered by subcontractor companies may need to be reconciled carefully, and incomplete CIS records can make the year-end HMRC position harder to verify. For VAT-registered companies, the VAT position and Corporation Tax position are separate, but errors in sales, purchases or cut-off can affect both. Payroll also matters, particularly where director salaries, bonuses, pension contributions or employment taxes have not been processed correctly.

Good Corporation Tax compliance is therefore not just about remembering a deadline. It depends on whether the accounting system has been kept in a condition that allows the company to know its profit with reasonable confidence.

What companies often get wrong

The most damaging errors are rarely exotic. They are ordinary misunderstandings repeated across small companies because the deadlines look more familiar than they really are.

Confusing the CT600 filing deadline with the payment deadline

This is the classic mistake. A director sees that the Corporation Tax return is due 12 months after the period end and assumes the tax is due at the same time. By the time the return is prepared, the payment may already be late.

Relying on Companies House filing as proof of HMRC compliance

Accounts filed at Companies House do not replace the Corporation Tax return. HMRC generally requires a Company Tax Return, computations and accounts in the required format. The accounts filed publicly may also be abbreviated or filleted, whereas HMRC receives more detailed tax information.

Leaving the tax estimate until the accounts are finalised

Final accounts are important, but the company usually needs a tax estimate before the CT600 deadline. If bookkeeping is current, that estimate should be manageable. If records are reconstructed late, the estimate becomes stressful and sometimes inaccurate.

Assuming dormant means “nothing to do”

A company may be dormant for Companies House purposes, inactive for Corporation Tax purposes, or simply not trading yet. These are related ideas but not always identical in administration. HMRC may still issue notices or expect a response unless the company’s status is correctly handled.

Ignoring changes in accounting period

Changing a company year end can alter filing dates and may create short or split Corporation Tax periods. It is worth checking the tax consequences before assuming the deadline has simply moved in a straightforward way.

Late payment, late filing and penalties

Late Corporation Tax payment and late Corporation Tax return filing are treated differently.

If Corporation Tax is paid late, HMRC may charge interest from the day after the payment due date. Interest is designed to compensate for late payment rather than operate as a fixed penalty. The longer the tax remains unpaid, the more interest can accrue.

If the Company Tax Return is filed late, HMRC can charge penalties. These usually start with a fixed penalty and can increase if the return remains outstanding. Repeated lateness may increase the amount. Additional tax-related penalties may arise in more serious cases where inaccuracies are careless or deliberate, though the facts matter and businesses should avoid assuming every correction is treated the same way. Where penalties have already been issued, the practical question is whether the evidence supports appealing HMRC penalties rather than simply disputing them informally.

Companies House has its own late filing penalties for accounts, separate from HMRC. A company can therefore face consequences from both regimes if accounts and tax obligations are not managed properly.

The practical point is not to treat penalties as the main story. The wider issue is credibility and control. Late filing can disrupt borrowing, tendering, investor discussions, director planning and routine business administration. For small companies, the immediate cash cost may be less damaging than the management time spent untangling the problem.

Large companies and quarterly instalment payments

The standard 9 months and 1 day rule applies to many small and medium-sized companies, but larger companies may need to pay Corporation Tax by quarterly instalments. This is a different regime with earlier payment dates and more demanding forecasting requirements.

A company may be affected if its taxable profits exceed relevant thresholds, adjusted for associated companies. The rules can become more involved where groups, related companies or fluctuating profits are present. For very large companies, the instalment timetable is earlier still.

The important distinction is that the standard deadline should not be assumed indefinitely as a company grows. A business that has moved from modest profits to substantially higher profits may need to revisit its Corporation Tax payment timetable before the year end, not after it.

Cashflow planning: Corporation Tax is not spare cash

Corporation Tax is calculated on taxable profits, but it is paid in cash. That sounds obvious until a company has used available cash for stock, dividends, equipment, loan repayments or expansion before reserving funds for tax.

Profit and cash are not the same. A company may show taxable profit while customers have not yet paid. Another may have cash in the bank because VAT has been collected but not yet paid over. A director may see a healthy balance and approve dividends without allowing for Corporation Tax, PAYE, VAT or supplier commitments.

A sensible process is to review Corporation Tax provision during the year, especially after profitable quarters. This does not need to be elaborate. Even a simple rolling estimate can help directors understand how much cash is truly available and how much should be set aside. Forward-looking corporate tax planning is most useful when it informs cashflow and decision-making before the year end, not only after the accounts are complete.

Dividends deserve particular care. They are paid from distributable profits after considering the company’s financial position. If accounts are out of date, directors may not have a reliable view of available profits. Corporation Tax does not itself determine whether a dividend is lawful, but poor tax visibility often goes hand in hand with poor dividend decision-making.

How VAT, payroll and CIS can affect the Corporation Tax picture

Corporation Tax is a separate tax, but it does not exist in isolation. The figures used in the tax computation come from the accounting records, and those records are shaped by other compliance systems.

VAT errors can distort turnover, expenses and balance sheet liabilities. A business using Making Tax Digital software may still have inaccurate records if transactions are coded incorrectly or bank feeds are not reviewed. Timely VAT filing is not the same as having clean accounts, but VAT records often reveal whether sales, purchases and liabilities have been handled consistently.

Payroll affects Corporation Tax because wages, employer National Insurance and pension costs may be deductible where properly incurred for the business. Director payroll needs particular attention because late decisions about salary, bonuses or pension contributions can have tax and reporting consequences.

CIS can matter for construction businesses on both sides of the contractor-subcontractor relationship. Deductions, verification, monthly returns and subcontractor statements can all affect records. A company that has suffered CIS deductions may need those amounts correctly reflected when calculating its overall HMRC position.

These areas do not change the basic Corporation Tax due date. They affect whether the company can calculate the right amount in time.

A practical workflow for staying ahead of the deadline

The strongest Corporation Tax processes are usually unremarkable. They rely on regular bookkeeping, early review and clear ownership rather than a dramatic year-end push.

A practical workflow might look like this:

• During the year: keep bank reconciliations current, code income and expenses consistently, maintain payroll and VAT records, and review director loan balances.
• Shortly after the year end: close off sales and purchase cut-off, collect missing invoices, reconcile payroll, review VAT control accounts and identify unusual transactions.
• Before the payment deadline: prepare a Corporation Tax estimate based on the best available accounts, check the HMRC payment reference and set aside or pay the expected liability.
• Before the filing deadline: finalise statutory accounts, tax computations and the CT600, then submit the return to HMRC.

The timing does not need to be perfect to be effective. What matters is avoiding a situation where the first serious review happens after the tax payment date has passed.

Questions directors should ask before the due date

Directors do not need to become tax technicians, but they do need enough visibility to know whether the company is under control. Before the Corporation Tax payment deadline, useful questions include:

• Is the bookkeeping complete up to the year end?
• Have bank accounts, credit cards and loan accounts been reconciled?
• Are payroll, pension and PAYE records reflected correctly?
• Have VAT returns been reviewed against the accounts?
• Are CIS deductions or contractor obligations properly recorded?
• Are director expenses, mileage claims and personal payments supported?
• Has a realistic Corporation Tax estimate been prepared?
• Is cash reserved for Corporation Tax separate from VAT, PAYE and operating funds?
• Are Companies House and HMRC deadlines both being tracked?

These questions often reveal whether the issue is a tax deadline problem or a wider finance process problem. If the company cannot answer them comfortably, the Corporation Tax deadline may simply expose weaknesses that already exist.

What to do if the Corporation Tax deadline is approaching

If the deadline is close and the accounts are not complete, the company should still work towards a reasonable estimate. Waiting for perfect information can be worse than making a carefully supported payment based on the records available.

The immediate priorities are usually to reconcile the bank, check sales and purchase records, review payroll and VAT balances, identify major adjustments, and estimate taxable profit. If the final liability later differs, the company can deal with the difference through further payment, repayment or offset as appropriate.

If the deadline has already passed, it is usually better to address the position promptly rather than delay because the exact number is still being refined. Late payment interest can continue to accrue. Filing obligations also remain in place, so the CT600 and accounts should still be completed properly.

Where HMRC has issued penalties or correspondence, the response should be based on the facts. Some penalties may be appealable where there is a reasonable excuse, but not every business difficulty will meet that threshold. Records, dates, correspondence and evidence matter.

Why deadline discipline improves more than compliance

Corporation Tax deadlines are often treated as a narrow compliance issue. In practice, they are a useful test of financial management.

A company that can estimate its tax position early usually has better visibility over margins, cashflow, dividends, investment capacity and director remuneration. It is less likely to confuse VAT cash with profit, less likely to discover payroll issues late, and better placed to make decisions before the year end closes.

This matters especially for growing companies. As turnover increases, weak bookkeeping becomes more expensive. Small coding errors multiply, VAT becomes more sensitive, payroll grows more complex, and director decisions carry larger consequences. Corporation Tax then becomes one part of a broader question: does the company’s finance function still match the size and complexity of the business?

Key takeaways on UK Corporation Tax deadlines

• Corporation Tax is usually due 9 months and 1 day after the end of the accounting period.
• The Corporation Tax return is usually due 12 months after the end of the accounting period.
• Companies House accounts deadlines are separate from HMRC Corporation Tax deadlines.
• First-year companies may have split Corporation Tax periods if accounts cover more than 12 months.
• Payment may be required before the final CT600 is filed, so early tax estimates matter.
• VAT, payroll, CIS and bookkeeping quality can all affect the accuracy of the Corporation Tax calculation.
• Large companies may fall under quarterly instalment payment rules rather than the standard timetable.
• Late payment can lead to interest, while late filing can trigger penalties.

A final perspective

The question “when is Corporation Tax due?” has a precise answer, but the practical challenge is broader. The deadline is manageable when records are current, responsibilities are clear and tax is treated as a planned business liability rather than a year-end surprise.

For most UK limited companies, the rule to remember is 9 months and 1 day for payment, 12 months for filing. The judgement sits around everything that happens before those dates: bookkeeping discipline, cashflow planning, payroll accuracy, VAT control, CIS records where relevant, and directors having a reliable view of profit before decisions are made.

Corporation Tax compliance is not just a submission exercise. It is a reflection of how well the company understands its own numbers.