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FILE IT YOURSELF, ONLINE

How to file a UK limited company tax return online

A practical route through the CT600 for directors of straightforward micro-entities. See which filings are separate, check the deadlines and accounts regime, then prepare and review your figures before submitting.

Start your CT600 filing Documents checklist

01 / TWO SEPARATE FILINGS

What a limited company files each year

A Company Tax Return goes to HMRC: CT600 Version 3 return data, normally with iXBRL accounts and a tax computation, plus applicable supplementary pages. Annual accounts go to Companies House as a separate filing, with a separate deadline and submission result. A confirmation statement is another Companies House obligation and is not covered by this guide.

HMRC's free joint online filing service, CATO, closed on 31 March 2026. Online Company Tax Returns now normally use commercial software; paper returns are permitted only in limited circumstances. Read about the closure of HMRC's free CT600 filing service or start with the CT600 preparation guide.

02 / KEEP THE DATES SEPARATE

Online filing deadlines

12 monthsA CT600 is normally due 12 months after its Corporation Tax accounting period ends.
9 months + 1 dayCorporation Tax is normally payable by this point after the period ends, for companies outside the instalment-payment regime.
9 monthsCompanies House annual accounts are normally due nine months after the accounting reference date. First accounts are normally due 21 months after incorporation.

For CT600 returns with a filing date on or after 1 April 2026, HMRC's fixed penalty is £200 when the return is late and a further £200 when it is more than three months late (£400 in fixed penalties overall). For three successive late returns, the amounts rise to £1,000 and a further £1,000 (£2,000 overall). Other penalties may also apply. Companies House has its own, separate late-accounts penalty regime.

Sources: GOV.UK CT600 penalty increase, GOV.UK annual accounts deadlines, GOV.UK late-accounts penalties, and the Corporation Tax deadlines and penalties guide.

03 / ACCOUNTS REGIME

Do you qualify for FRS 105 micro-entity accounts?

For financial years beginning on or after 6 April 2025, a company generally meets the micro-entity size test when it satisfies at least two of three limits: turnover of no more than £1 million, balance sheet total of no more than £500,000, and an average of no more than 10 employees. The previous turnover and balance sheet limits were £632,000 and £316,000. Qualification generally takes account of two consecutive financial years, with special rules for a company's first year.

Some entities cannot use the micro-entity regime, including charities and certain financial or investment entities. FRS 105 does not permit fair value accounting, and a parent preparing group accounts may face an exclusion. Use the checker as a prompt, then check the full statutory rules for your company.

INDICATIVE CHECK

Check your FRS 105 position

Micro-entity size test

Enter figures for the financial year being assessed. All three fields are required; an empty field is not treated as zero.

Limit: £1,000,000
Limit: £500,000
Limit: 10

Select any that apply:

Size test pending

Enter all three figures to see an indicative result.

Indicative only. This checker does not determine statutory eligibility, apply every two-year transition rule or assess every exclusion. Check the full rules before choosing an accounts regime.

Compare micro-entity accounts with small-company accounts. See also GOV.UK guidance on micro-entities, small and dormant companies.

04 / PREPARE YOUR RECORDS

Information to prepare

Gather your company UTR, Corporation Tax-enrolled Government Gateway credentials, accounting-period dates, trial balance or bookkeeping records, and prior-year figures. If filing accounts with Companies House, you will also need its authentication code. Keep details of capital asset purchases and director loans to hand where relevant. The documents checklist helps you identify what applies; keep credentials secure.

05 / THE WORKFLOW

File online in 5 steps

  1. Add your company and confirm the period

    WeFile retrieves company details and expected accounts periods from Companies House where applicable. Check the dates against HMRC’s notice to deliver before continuing.

  2. Enter or import your profit and loss figures

    Enter figures yourself or import bookkeeping data from Xero, QuickBooks Online, FreeAgent or CSV. Review the imported figures before using them.

  3. Complete the balance sheet and capital allowances

    Enter assets, liabilities and qualifying capital expenditure. The profit and loss account and balance sheet must reconcile before continuing.

  4. Review the tax computation and generated accounts

    WeFile calculates supported Corporation Tax, including Marginal Relief, and generates accounts under the selected FRS 105 or FRS 102 regime. Check every figure and document.

  5. Submit to HMRC and, where applicable, Companies House

    Use your Corporation Tax-enrolled Government Gateway credentials and, for a Companies House submission, its authentication code. The two submissions are tracked separately; an IRmark is shown when HMRC supplies one.

For the submission and receipt stages, see how CT600 submission to HMRC works. For more preparation detail, follow the online CT600 filing walkthrough.

06 / CHOOSE THE RIGHT HELP

Filing yourself vs using an accountant

DIY software and accountant-prepared filing
QuestionWeFile (DIY)Traditional accountant
Who prepares the figures?You, with a guided workflow.The accountant prepares them using your records.
Cost
Fees vary by firm and scope; request quotes.
Tax advice and planningNot provided. WeFile is software, not an accountancy service.Typically included or available; confirm the agreed scope.
Tax calculation and reconciliation checksAutomatic for supported circumstances.Depends on the firm's software and service.
Responsibility for accuracyThe director remains responsible.The director remains legally responsible.
Best suited toStraightforward micro-entities or dormant companies with reliable records.Complex affairs, groups, R&D claims or unsupported supplementary pages.

If you are unsure which route suits your circumstances, consult a qualified accountant.

07 / REVIEW BEFORE SENDING

Common CT600 mistakes to avoid

Wrong accounting periodA CT600 period cannot exceed 12 months. WeFile splits a longer accounts period into two returns where applicable; check the dates against HMRC's records.
UTR or company-number mismatchCheck identifiers against your records before submission. An incorrect pairing can cause HMRC to reject or later query a return.
Disallowable expenses overlookedDepreciation and client entertaining are examples to review. WeFile provides tax-adjustment fields to add back disallowable amounts; you must identify and enter the correct figures. See the allowable expenses guide.
Depreciation claimed instead of capital allowancesAccounting depreciation and tax relief are different. Enter qualifying expenditure in the appropriate capital-allowances fields and review the computation.
Balance sheet does not reconcileCheck profit, retained earnings and opening balances. WeFile checks that the profit and loss account and balance sheet reconcile before continuing.
Supplementary pages missedDirector loans may require CT600A supplementary pages. Review which pages apply; WeFile does not support every supplementary page.
Associated companies ignoredThey can change Marginal Relief limits. WeFile provides an associated-companies input for the supported calculation; check the number entered.
Government Gateway not enrolledConfirm that the account you use is enrolled for Corporation Tax. Reconciliation checks cannot resolve an authentication failure.

If a submission fails, use the reported reason to investigate it. Read the guide to HMRC CT600 submission errors; do not assume an electronic receipt means every later HMRC check has passed.

QUESTIONS, ANSWERED

Limited company online filing FAQs

Yes. A director can prepare and file a CT600 Version 3 return using suitable software without appointing an accountant, provided the company’s circumstances are supported. The director remains responsible for the accuracy and completeness of the return. Consider qualified advice for complex circumstances.
A Company Tax Return is normally due 12 months after the Corporation Tax accounting period ends. Corporation Tax payment is normally due nine months and one day after period end for companies outside the instalment-payment regime. Companies House accounts have a separate deadline.
For financial years beginning on or after 6 April 2025, the micro-entity size test generally requires at least two of: turnover no more than £1 million, balance sheet total no more than £500,000, and an average of no more than 10 employees. Two-year qualification rules and exclusions also apply. The page’s checker is indicative only; check the full statutory rules.
Gather the company UTR, Corporation Tax-enrolled Government Gateway credentials, period dates, bookkeeping or trial-balance figures, and relevant prior-year figures. If filing accounts with Companies House, you will need its authentication code. Capital purchases and director loans may require additional details.
You enter or import the figures. WeFile checks that the profit and loss account and balance sheet reconcile, generates accounts for supported regimes, and calculates supported Corporation Tax, including Marginal Relief. You must review the inputs and outputs: WeFile does not audit your records or provide accountancy advice.
WeFile charges a price per filing; an accountant’s fees vary by firm, work and scope, so request quotes for your circumstances rather than assuming a saving. WeFile is software and does not provide tax advice or planning.
WeFile supports dormant filings where applicable. Dormant Companies House accounts and a CT600 are separate obligations: a dormant company needs to submit a CT600 if HMRC has issued a notice to deliver a Company Tax Return and has not withdrawn it. Check its position with HMRC before filing.

Ready to start your CT600 filing?

Prepare your figures, review the documents and track each submission separately.

Start your CT600 filing

This guide and eligibility checker provide general information, not professional accounting or tax advice. Directors remain responsible for accurate, complete and timely filings. Check the rules that apply to your circumstances and consult a qualified professional where needed.