The Complete Guide to UK Company Accounts — What Must Be Filed and When (2026)

The Two Filing Obligations Every UK Ltd Has

1. Companies House: Annual Accounts These are statutory accounts — a formal financial statement of the company's financial position and performance for the year. They are publicly accessible at Companies House by anyone.

2. HMRC: Corporation Tax Return (CT600) The CT600 is the company's tax return — it calculates the taxable profit and the Corporation Tax due. It is not public. It goes to HMRC alongside a copy of the statutory accounts (same accounts, but the CT600 version includes additional tax schedules).

These two obligations have different deadlines and different content requirements. Confusion between them is common and causes compliance failures.

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Companies House Accounts: Deadlines

• Example: Company incorporated January 1, 2024. Financial year end: December 31, 2024.
• First accounts: due 9 months after year end → September 30, 2025

Late filing penalties at Companies House (private companies):

These penalties are automatic — no warning, no discretion. They are also personally embarrassing (shown on the company's Companies House record permanently).

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Accounts Size Thresholds: What You Must File

Your company's size determines the level of accounts detail you must file publicly.

• Micro-entity (two of three conditions met):
• Turnover ≤ £632,000
• Balance sheet total ≤ £316,000
• Average employees ≤ 10

Micro-entities can file: an abridged balance sheet only. No P&L. No notes beyond the minimum. Most solo-founder companies qualify. The public filing is minimal — just a balance sheet showing assets and liabilities.

• Small company (two of three conditions met):
• Turnover ≤ £10.2M
• Balance sheet total ≤ £5.1M
• Average employees ≤ 50

Small companies must file: balance sheet + notes. They are exempt from filing the P&L publicly (can keep trading performance private). Still qualify for audit exemption.

• Medium company (two of three conditions met):
• Turnover ≤ £36M
• Balance sheet total ≤ £18M
• Average employees ≤ 250

Medium companies must file full accounts including P&L and directors' report. Audit required unless exempt.

Large company: Above medium thresholds — full statutory accounts with mandatory audit.

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HMRC Corporation Tax: Deadlines

CT600 filing deadline: 12 months after the end of the accounting period.

CT payment deadline: 9 months and 1 day after the end of the accounting period.

• Example: Financial year end December 31, 2025:
• CT payment due: October 1, 2026
• CT600 return due: December 31, 2026

Note: CT payment is due BEFORE the return. You must calculate and pay your CT based on your own calculation (or your accountant's), and then formally file the return within the longer deadline.

Large companies (CT liability > £1.5M): Must pay CT in quarterly instalment payments during the accounting year — not 9 months after.

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What Goes Into a CT600

• The CT600 itself is a multi-section form filed online via HMRC's Corporation Tax Online Service (or via third-party accounting software). It covers:
• Company details and accounting period
• Trading income
• Adjustments to accounting profit to arrive at taxable profit (add back: depreciation; deduct: capital allowances, R&D enhanced deductions)
• Losses carried forward from previous years
• Capital gains (if any)
• Tax calculation (applying the correct CT rate: 19% small profits, 25% main rate, or tapered rate between)
• Reliefs and claims (R&D credits, group relief, etc.)

• Alongside the CT600, you file:
• A copy of the full statutory accounts (not the abbreviated Companies House version — the full P&L, balance sheet, and notes)
• CT600 supplementary pages (e.g., for R&D claims, group structures, foreign income)

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Accounting Periods

A company's accounting period for CT purposes is usually 12 months, aligned with its Companies House financial year. But if your accounting period exceeds 12 months (common for first-year companies with a long initial period), HMRC splits it into two periods — first 12 months, then the remainder — each with their own CT obligations.

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Making Tax Digital (MTD) for Corporation Tax

MTD for CT is not yet mandatory (as of 2026). A voluntary pilot exists. Mandatory MTD for CT is expected no earlier than April 2026 for the largest companies, with broader rollout in subsequent years. Monitor HMRC announcements — mandatory requirements will require MTD-compatible software for CT returns.

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FAQs

Can I file my own CT600 without an accountant? Technically yes — HMRC's Corporation Tax Online service allows direct filing. In practice: correctly calculating taxable profit (adjusting for capital allowances, R&D deductions, etc.) requires accounting knowledge. Errors are easily made and can result in underpaying (penalties) or overpaying (missed claims). For anything beyond a simple company with no complex transactions, use an accountant.

What if I can't pay the CT bill on time? File the CT600 on time regardless of whether you can pay — the late filing penalty and late payment interest are separate. Contact HMRC's Time to Pay service before the payment deadline to negotiate an instalment arrangement. Interest accrues on unpaid CT at the HMRC late payment rate (currently 7.5%) from the due date.

Are the accounts I file at Companies House the same as what I give HMRC? No — typically different. Companies House receives an abbreviated version (for micro/small companies: balance sheet only). HMRC receives the full accounts (complete P&L, balance sheet, notes). Your accountant prepares both versions from the same underlying accounts.

Do I need to file accounts if my company made no profit? Yes. Annual accounts and CT600 must be filed regardless of profitability. A loss-making company files its accounts showing the loss — the loss is carried forward and reduces future CT liability. Filing obligations do not depend on profitability.

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