UK Ltd Corporation Tax Dates & Deadlines

Corporation Tax is the main tax on company profits in the UK, administered by HM Revenue & Customs (HMRC). Every private limited company must pay Corporation Tax on its taxable profits (after allowable deductions and reliefs), even if profits are low or zero in some years. The current main rate is 25% for profits over £250,000 (with marginal relief and small profits rate of 19% for profits up to £50,000, tapered between £50,000–£250,000 as of recent rules).

Deadlines depend on your company's accounting period (usually matching your financial year-end or accounting reference date). This is the period covered by your accounts and tax computations. Most companies align it with their Companies House year-end for simplicity.

Key requirements include registering for Corporation Tax, calculating liability accurately, paying on time, and filing a Company Tax Return (form CT600) with supporting accounts and computations in iXBRL format.

1. Registering for Corporation Tax

You must notify HMRC that your company is within the scope of Corporation Tax within 3 months of starting to trade or becoming active (e.g., after incorporation if you begin business activities).

• Do this via your HMRC online business tax account or by contacting HMRC.
• Failure to register on time can lead to penalties or interest.
• HMRC will then issue a Unique Taxpayer Reference (UTR) if not already assigned and set your first accounting period (often from incorporation to your chosen year-end).

For new companies, this is one of the first post-incorporation steps after setting up your business tax account.

2. Corporation Tax Payment Deadline

Corporation Tax must be paid 9 months and 1 day after the end of your accounting period.

This is the key date most directors remember, as late payment incurs interest (currently around Bank of England base rate + 2.5%).

Examples:

• Accounting period ends 31 March 2025 → Payment due 1 January 2026.
• Accounting period ends 30 April 2025 → Payment due 1 February 2026.
• Accounting period ends 31 December 2025 → Payment due 1 October 2026.

Special rules for larger companies:

• If taxable profits exceed £1.5 million (reduced pro-rata for associated companies), you pay in quarterly instalments (Payments on Account), starting earlier in the period.
• For very large groups (profits over £20 million), instalments are due in the 3rd, 6th, 9th, and 12th months of the accounting period.

Most small and medium limited companies pay in one lump sum 9 months +1 day after year-end.

3. Company Tax Return (CT600) Filing Deadline

You must file your Company Tax Return (CT600) within 12 months of the end of the accounting period.

This return includes:

• Self-assessment of profits and tax due.
• Full statutory accounts (profit & loss, balance sheet).
• Tax computations showing how taxable profit was calculated.
• All in iXBRL (inline XBRL) format for electronic submission.

Examples:

• Accounting period ends 31 March 2025 → CT600 due 31 March 2026.
• Accounting period ends 31 December 2025 → CT600 due 31 December 2026.

File online via HMRC's portal (mandatory for most companies). Even dormant companies or those with no tax due must file a return (often a short "nil" return).

4. First-Year Special Rules

For your very first accounting period:

• It may be shorter or longer than 12 months (up to 18 months max if you choose).
• Register within 3 months of starting to trade.
• HMRC notifies you of your accounting period dates.
• Payment and filing deadlines follow the standard rules based on that first period's end date.

If accounts cover more than 12 months, split into multiple returns (accounting periods cannot exceed 12 months).

5. Penalties for Late Filing or Payment

• Late CT600 filing: Starts at £100 (up to 3 months late), rises to £200 (3–6 months), then daily penalties and tax-geared penalties (up to 10% of tax due) for longer delays. From April 2026, some penalties increase.
• Late payment: Interest accrues daily; no fixed penalty but potential surcharges in severe cases.
• Always pay first (even if estimating), then file the return later—HMRC allows corrections via amended returns.

6. Other Key Requirements and Tips

• Accounting period alignment: Keep your HMRC accounting period in line with Companies House (file annual accounts 9 months after year-end). Notify HMRC of changes promptly to avoid penalties.
• Supporting documents: Maintain accurate records (invoices, receipts, bank statements) for at least 6 years.
• Dormant companies: Still file CT600 if required, but often simplified.
• Professional help: Many use accountants to prepare CT600, computations, and iXBRL tagging to ensure accuracy and avoid errors.
• Updates: Check GOV.UK for latest rates, thresholds, or reliefs (e.g., full expensing, R&D credits).

Quick Reference Table: Standard Deadlines

Corporation Tax deadlines are tied to your accounting period end date, not a fixed calendar like Self Assessment. Mark your year-end +9 months +1 day for payment and +12 months for filing. Missing these can lead to interest, penalties, or compliance issues that affect your company's standing.

For new or growing limited companies, set calendar reminders early and consider professional support to handle calculations, iXBRL, and submissions smoothly.

Always refer to official GOV.UK guidance for your specific situation, as rules can update (e.g., for large companies or reliefs).

Staying compliant keeps your business focused on growth rather than HMRC queries.

Disclaimer: The information provided in this article is for general informational and research purposes only. Company details, features, services, and market positions may change over time. Readers are advised to visit official company websites and conduct independent research before making any business decisions or purchasing services.