Company Tax Return Filing in 2026: What UK Limited Companies Need to Know About HMRC Software Rules

The way UK companies file their Company Tax Returns has changed significantly in 2026.

HMRC's previous online service for filing company accounts and Company Tax Returns closed on 31 March 2026. Businesses that previously relied on that service now generally need to use commercial software to submit their Company Tax Return to HMRC. GOV.UK

HMRC continues to maintain a list of software providers capable of producing and submitting Corporation Tax returns, CT600 forms and iXBRL accounts. That list was updated again on 29 September 2026, making this a good time for company directors to check that their filing arrangements are still suitable. GOV.UK

What Changed in April 2026?

Until the end of March 2026, some smaller businesses could use HMRC's joint online service to submit their company accounts and Corporation Tax return.

That service is no longer available.

From 1 April 2026, businesses that previously used it need to use appropriate commercial software to file their Company Tax Return with HMRC. Paper Corporation Tax returns are generally only permitted where there is a reasonable excuse or where the return is being filed in Welsh. GOV.UK

For many small companies, this means reviewing how their accountant or accounting software prepares and submits the CT600.

What Is a Company Tax Return?

A Company Tax Return is the information a company provides to HMRC so that its Corporation Tax liability can be calculated.

A return can be required even where the company:

• made a loss;
• has no Corporation Tax to pay; or
• believes little or no tax is due.

If HMRC issues a notice requiring a Company Tax Return, the company must normally submit one. GOV.UK

The return generally involves calculating:

• taxable company profits;
• allowable expenses;
• relevant tax adjustments;
• capital allowances;
• applicable reliefs; and
• the Corporation Tax payable.

The accounting profit shown in a company's accounts is not necessarily the same as the taxable profit used to calculate Corporation Tax.

What Software Do Companies Need?

HMRC does not require every business to use one particular brand.

Instead, HMRC publishes information about commercial products and providers that can produce one or more parts of a Company Tax Return.

These can include software capable of:

• preparing and submitting CT600 returns;
• producing iXBRL accounts;
• producing iXBRL tax computations;
• preparing supplementary Corporation Tax pages; and
• filing certain accounts and tax information electronically.

HMRC updated its recognised supplier list on 29 September 2026, adding another provider to its CT600 and integrated iXBRL sections. GOV.UK

HMRC does not recommend one supplier over another, so businesses should choose software based on their actual requirements. GOV.UK

What Is iXBRL?

iXBRL stands for Inline eXtensible Business Reporting Language.

It is a digital reporting format that allows financial information in accounts and tax computations to be electronically tagged.

For most businesses, the technical tagging is handled by their accounting or Corporation Tax software.

You usually do not need to manually understand every iXBRL tag, but the software or professional adviser preparing the return needs to produce compliant information.

HMRC's guidance recommends making sure the software used can produce a fully compliant Company Tax Return and the necessary iXBRL accounts and computations. GOV.UK

Can You Still File Accounts Directly With Companies House?

It is important to distinguish HMRC Corporation Tax filing from Companies House accounts filing.

They are related, but they are not the same thing.

The old joint HMRC/Companies House filing service has closed, but Companies House currently still provides other ways of filing certain types of company accounts.

Depending on the type of accounts, options can currently include:

• Companies House online services;
• approved software; or
• paper filing in some circumstances.

However, Companies House has announced that from 1 April 2028 all companies will need to file annual accounts using commercial software. GOV.UK

So even businesses that are not currently using accounting software for Companies House filing should consider how their systems may need to change before 2028.

What Is the Deadline for Filing a Company Tax Return?

The Company Tax Return filing deadline is normally:

12 months after the end of the accounting period covered by the return.

For example, if a company's Corporation Tax accounting period ends on:

31 December 2026

the Company Tax Return would normally need to be filed by:

31 December 2027

There is, however, a separate deadline for actually paying Corporation Tax. GOV.UK

When Does Corporation Tax Need to Be Paid?

For many companies, Corporation Tax is normally due:

9 months and 1 day after the end of the accounting period. GOV.UK

This means the payment deadline can arrive before the Company Tax Return filing deadline.

Business owners sometimes confuse the two dates.

For example:

Obligation	Typical timing
Pay Corporation Tax	9 months + 1 day after accounting period ends
File Company Tax Return	12 months after accounting period ends

Large and very large companies can be subject to different payment rules, including instalment payments.

What Should Small Companies Check Now?

Companies that previously relied on HMRC's old online filing service should make sure they have a replacement process in place.

A useful checklist is:

1. Confirm your company's accounting year end.
2. Check your Corporation Tax payment deadline.
3. Check your Company Tax Return filing deadline.
4. Make sure bookkeeping is complete.
5. Confirm annual accounts are prepared correctly.
6. Check which software will prepare the CT600.
7. Confirm the software supports the necessary iXBRL accounts and computations.
8. Make sure any relevant Corporation Tax reliefs are considered.
9. Allow enough time to correct filing errors before the deadline.

Waiting until the return is due before deciding which software to use can create unnecessary pressure.

What If Your Accountant Files the Return?

If an accountant prepares and submits your Corporation Tax return, they will normally handle the technical software requirements.

However, company directors still need to provide complete and accurate accounting information.

That can include:

• sales records;
• purchase invoices;
• business expenses;
• payroll information;
• bank transactions;
• director transactions;
• asset purchases;
• loans;
• dividends; and
• other relevant financial records.

Using commercial software does not correct incomplete bookkeeping automatically.

The quality of the Company Tax Return still depends heavily on the underlying records.

Watch Out for Director's Loan Transactions

One area that commonly creates Corporation Tax complications is the director's loan account.

If directors take money from the company that is not:

• salary;
• reimbursement of legitimate expenses;
• a dividend; or
• repayment of money previously lent to the company,

it may be recorded through a director's loan account.

Depending on the balance and timing, additional Corporation Tax consequences can arise.

Directors should therefore make sure these transactions are properly recorded before the accounts and Company Tax Return are finalised.

What About Capital Allowances?

Businesses purchasing equipment, machinery and other qualifying assets should also check whether capital allowances are available.

The accounting treatment of an asset does not always determine the Corporation Tax deduction.

Tax rules can provide different allowances depending on the type of expenditure and the circumstances.

This is another reason why simply transferring accounting profit into a Corporation Tax return without appropriate tax adjustments can produce the wrong result.

Why Good Bookkeeping Matters

The move towards software-based tax filing makes regular bookkeeping increasingly important.

Accurate records help ensure that:

• income is reported correctly;
• allowable expenses are identified;
• VAT records agree where relevant;
• payroll information is consistent;
• capital expenditure is identified;
• director transactions are correctly recorded; and
• the Corporation Tax calculation can be prepared efficiently.

Leaving bookkeeping until shortly before the filing deadline can make errors more likely.

What Happens If You File Late?

HMRC can charge penalties where a Company Tax Return is submitted late.

A late return can also create additional administrative work and potentially attract further HMRC attention.

The best approach is to keep the company's accounting and Corporation Tax timetable clear throughout the year rather than treating the return as a last-minute task.

Does Your Company Need to File If It Made a Loss?

Yes, potentially.

A company that receives a notice from HMRC to deliver a Company Tax Return generally still needs to file even if:

• it made a trading loss; or
• no Corporation Tax is payable. GOV.UK

Losses can also have tax implications because, depending on the circumstances, they may potentially be carried forward, carried back or otherwise relieved.

They should therefore be calculated and reported correctly.

How TaxMech Can Help

Corporation Tax filing is becoming increasingly software-driven, but good software is only one part of the process.

TaxMech Consultants Ltd can help businesses prepare accurate company accounts, review Corporation Tax calculations and ensure Company Tax Returns are prepared and filed correctly.

We can also help directors organise their accounting records, identify relevant tax adjustments and understand their Corporation Tax payment and filing deadlines.

If your business previously relied on HMRC's old online filing service or you are unsure whether your current accounting setup is suitable, reviewing the process before your next filing deadline can help avoid unnecessary problems.