Filing taxes as a business in the UK: 2026 guide

Sole traders file a Self Assessment return (SA100, with SA103 self-employment pages) each year; limited companies file a CT600 Company Tax Return to HMRC and statutory accounts to Companies House. Both routes start with registration, and both have separate deadlines for filing and for paying. Here is what you need to do right now:

• Register first. Sole traders must register for Self Assessment if trading income exceeds £1,000 in a tax year. Limited companies must register for Corporation Tax with HMRC within three months of starting to trade.
• Find your UTR. Your Unique Taxpayer Reference arrives by post after registration and is required to log in and file.
• Gather 12 months of records. Sales invoices, purchase receipts, bank statements, and payroll records all feed into your return.
• Keep a separate business bank account. Mixing personal and business transactions is the single most common bookkeeping error HMRC flags.
• Note that filing and payment deadlines differ. Missing a payment deadline costs interest; missing a filing deadline costs a penalty. They are not the same date.
• Consider professional support. Concorde Company Solutions Limited, the leading accountancy practice in Garforth, Leeds, handles the full process from record-keeping to submission.

Key takeaways

Filing business taxes in the UK requires registering with HMRC for the correct return, keeping accurate records throughout the year, and meeting separate deadlines for filing and payment.

Table of Contents

• Which taxes apply to your business type?
• How to prepare and file taxes as a sole trader
• How limited companies file Corporation Tax and annual accounts
• When do you need to register for VAT and PAYE?
• What records must you keep, and which expenses can you deduct?
• Key deadlines, penalties, and how to correct mistakes
• Which filing route should you use, and what is Making Tax Digital?
• When should you hire an accountant?
• Filing taxes when your business has overseas income or operations
• Common tax reliefs and credits available to businesses
• How tax works for employee benefits and dividends
• How to prepare for an HMRC tax investigation or audit
• Concorde Company Solutions Limited: tax filing support for UK businesses
• Sources

Which taxes apply to your business type?

The return you file depends entirely on how your business is structured. Getting this wrong from the start means filing the wrong form, missing the right deadline, or both.

Sole traders pay Income Tax and Class 4 National Insurance on their trading profits through Self Assessment. If your turnover is above the VAT registration threshold set by HMRC, you must also register for VAT. Class 2 National Insurance is no longer a separate charge from the relevant recent tax year onwards, having been folded into the Self Assessment calculation.

Partnerships file a Partnership Tax Return (SA800) to report the partnership’s income and expenses. Each partner then files their own individual Self Assessment return, reporting their share of the profits on supplementary pages. The nominated partner is responsible for the SA800; every partner is responsible for their own SA100.

Limited companies face a dual obligation:

• File statutory annual accounts with Companies House (usually within nine months of the accounting period end for private companies).
• File a CT600 Company Tax Return with HMRC within 12 months of the accounting period end.
• Pay Corporation Tax nine months and one day after the accounting period ends — before the CT600 is even due.
• Register for PAYE if the company pays directors or employees above the Lower Earnings Limit.
• Register for VAT if turnover exceeds £90,000.

Beyond these core obligations, businesses with overseas income, property income, or capital gains need additional supplementary pages or separate returns. PAYE and VAT each carry their own registration thresholds, filing schedules, and penalty regimes, covered in detail below.

How to prepare and file taxes as a sole trader

Filing Self Assessment for the first time feels complicated until you break it into discrete steps. Follow these in order and the process becomes manageable.

1. Register for Self Assessment. Do this by 5 October following the end of the tax year in which you started trading. HMRC then sends your UTR by post within ten working days. You need this to activate your Government Gateway account.
2. Set up your Government Gateway account. Go to GOV.UK and sign in or create an account. You will need your UTR, National Insurance number, and proof of identity. HMRC’s guidance on filing Self Assessment online walks you through activation.
3. Gather your records. You need total income from self-employment, all allowable business expenses with receipts, any other income (employment, property, savings), and your National Insurance number. The MoneyHelper Self Assessment guide lists the full documentation checklist.
4. Calculate taxable profit. Deduct allowable expenses from your trading income. You can use either cash basis (record money when it is received or paid) or traditional accruals accounting. Capital allowances apply to equipment and vehicles under traditional accounting; the Annual Investment Allowance covers most small business equipment purchases.
5. Complete the SA100 and SA103. The SA100 is the main return; the SA103 self-employment pages capture your trading income and expenses. The SA103F helpsheet for 2025–2026 explains every box, including how to claim the trading income allowance (£1,000) and how to record provisional figures if your accounts are not yet finalised.
6. Submit online by 31 January. The online filing deadline for the 2025/26 tax year is 31 January 2027. Paper returns must be submitted by 31 October 2026. HMRC’s completion guide confirms that the vast majority of taxpayers file online, and the process is straightforward once your records are in order.
7. Pay your tax bill by 31 January. The balancing payment for 2025/26 and the first payment on account for 2026/27 are both due on 31 January 2027. A second payment on account falls on 31 July 2027.

Pro Tip: If your accounts are not finalised before the filing deadline, you can submit provisional figures and amend the return later. Mark the figures as provisional in the relevant boxes on the SA103 — the SA103F helpsheet explains exactly how. Do not miss the deadline waiting for perfect numbers.

For a detailed walkthrough of the calculation side, the sole trader tax return guide from Concorde Company Solutions Limited covers the full process with worked examples.

How limited companies file Corporation Tax and annual accounts

Limited companies carry two separate sets of obligations that run on different timelines. Conflating them is one of the most common and costly mistakes directors make.

Step 1: Register at Companies House and with HMRC. Incorporating at Companies House automatically notifies HMRC, but you must still register for Corporation Tax separately within three months of starting to trade. HMRC sends a CT41G form; completing it promptly avoids late registration penalties.

Step 2: Prepare statutory annual accounts. These are the full financial statements (profit and loss account, balance sheet, notes) prepared to UK GAAP or FRS 105/102 standards. Private limited companies must file these with Companies House, typically within nine months of the accounting period end. The accounts also form the basis of the tax computation.

Step 3: Prepare the Corporation Tax computation. This is a separate document that adjusts the accounting profit for tax purposes, adding back disallowable expenses and applying reliefs such as capital allowances or R&D credits. The computation supports the CT600.

Step 4: Complete and file the CT600. The CT600 guide on GOV.UK explains every section of the return, including company information, income, deductions, and supplementary pages. You must file a Company Tax Return even if the company made a loss or owes no Corporation Tax — HMRC issues a “notice to deliver” and the obligation stands regardless of profit.

Step 5: iXBRL tagging. Accounts and computations submitted with the CT600 must be tagged in iXBRL format. This is a technical requirement that most general-purpose spreadsheet software cannot handle. Specialist software or an accountant is almost always necessary here.

The timeline below shows the key dates relative to the accounting period end:

GOV.UK’s limited company accounts guidance is the authoritative source for these deadlines.

Pro Tip: Reconcile your bookkeeping to your draft accounts before you start the tax computation. Discrepancies between your accounting records and your bank statements are far easier to resolve at year-end than six months later when HMRC asks questions. If your accountant is preparing the CT600, give them clean, reconciled records — it cuts their time and your bill.

The company accounts filing guide from Concorde Company Solutions Limited covers the statutory accounts preparation process in detail.

When do you need to register for VAT and PAYE?

These two obligations catch many small business owners off guard because they kick in based on thresholds, not business structure.

VAT registration:

• You must register for VAT when your taxable turnover exceeds £90,000 in any rolling 12-month period.
• Voluntary registration below the threshold is worth considering if your customers are VAT-registered businesses, since you can reclaim input VAT on purchases.
• Once registered, you submit VAT returns (usually quarterly) and pay any VAT owed to HMRC. Making Tax Digital for VAT applies to all VAT-registered businesses, meaning you must keep digital records and submit returns through MTD-compatible software.
• Reclaiming VAT changes your bookkeeping: you record net amounts for expenses and track input and output VAT separately.

PAYE registration:

• Register as an employer with HMRC before your first payday if you pay any employee (including a director) above the Lower Earnings Limit (£6,396 per year for 2025/26).
• Run payroll each pay period and submit a Full Payment Submission (FPS) to HMRC on or before each payday using Real Time Information (RTI).
• Pay PAYE and National Insurance to HMRC by the 19th of the following month (22nd if paying electronically).
• Payroll services for small businesses from Concorde Company Solutions Limited cover RTI submissions and ongoing payroll management if you prefer to outsource.

GOV.UK’s VAT registration and employer PAYE pages are the definitive sources for current thresholds and the online registration routes.

What records must you keep, and which expenses can you deduct?

HMRC does not prescribe a specific format for business records, but it does specify what you must be able to produce and for how long.

Core records to keep:

• Sales invoices and receipts for all income
• Purchase invoices and receipts for all business expenses
• Bank statements (business account, separate from personal)
• Payroll records if you employ staff
• VAT records if registered (digital records under MTD)
• Mileage logs for vehicle use claims
• Evidence for capital expenditure (asset purchases, disposal proceeds)

How long to keep them: Self-employed individuals must keep records for at least five years after the 31 January submission deadline for the relevant tax year. Limited companies must keep accounting records for six years from the end of the accounting period.

Allowable expenses reduce your taxable profit. Common categories include:

• Office costs (stationery, phone, broadband)
• Travel and subsistence (business journeys, not commuting)
• Staff costs (salaries, employer NI, pension contributions)
• Marketing and advertising
• Professional fees (accountancy, legal)
• Stock and materials
• Use of home as office (a proportion of household costs)

Capital expenditure on equipment, vehicles, or fixtures is not an allowable revenue expense, but you can claim capital allowances (including the Annual Investment Allowance) to reduce taxable profit. The SA103F helpsheet covers the self-employment expense boxes in detail.

The single most common record-keeping mistake is mixing personal and business transactions in the same bank account. It makes it almost impossible to produce accurate accounts quickly, and it raises questions during any HMRC enquiry. A dedicated business account costs little and saves hours.

Key deadlines, penalties, and how to correct mistakes

Missing a deadline costs money. The penalty structure is tiered, and interest accrues separately from penalties, so a late payment and a late filing can both hit at once.

Penalty overview:

• Self Assessment late filing: £100 immediately; further daily penalties after three months; additional percentage-based penalties after six and twelve months.
• Corporation Tax late filing: £100 after one day; £200 after three months; percentage-based penalties for longer delays.
• Late payment interest: HMRC charges interest on unpaid tax from the due date. The rate is linked to the Bank of England base rate plus a margin.
• VAT: A points-based penalty system applies for late submissions; a separate percentage-based penalty applies for late payment.

If you miss the deadline, HMRC’s Time to Pay service allows eligible taxpayers to arrange a payment plan for Self Assessment debts. Contact HMRC before the deadline if you know you cannot pay in full.

Correcting mistakes: You can amend a Self Assessment return online within 12 months of the original filing deadline. For Corporation Tax, amendments are possible within 12 months of the CT600 filing deadline. For more significant errors, voluntary disclosure to HMRC is always preferable to waiting for them to find it.

Pro Tip: Treat your tax payment date and your filing date as two separate calendar events. Many business owners focus on the filing deadline and forget that the payment is often due at the same time or earlier. Set a reminder three months before the payment date to check your cashflow position — not the week before.

Which filing route should you use, and what is Making Tax Digital?

The method you use to submit returns matters as much as the returns themselves, particularly for limited companies where iXBRL is mandatory.

Making Tax Digital (MTD):

• MTD for VAT has applied to all VAT-registered businesses since April 2022. Digital records and MTD-compatible software are not optional.
• MTD for Income Tax is rolling out to qualifying self-employed individuals and landlords with income above the relevant threshold. Check GOV.UK’s MTD for income eligibility guidance to confirm whether and when it applies to you.
• The MTD impact on UK businesses article from Concorde Company Solutions Limited explains the operational changes in plain terms.

iXBRL for limited companies:

• Accounts and computations filed with the CT600 must be tagged in iXBRL (Inline eXtensible Business Reporting Language). This is a technical data-tagging standard that allows HMRC’s systems to read and validate the figures automatically.
• Manual iXBRL tagging is error-prone and frequently rejected. HMRC’s guidance on company tax return obligations makes clear that specialist software is the practical route for most companies.

Choosing software — what to look for:

• MTD compliance for VAT and (where applicable) Income Tax
• iXBRL support for company accounts and computations
• Direct submission to HMRC and Companies House
• HMRC recognition (check the approved software list on GOV.UK)
• Quality of user support and update frequency
• Pricing relative to your filing volume

Pro Tip: Test a file submission with your chosen software before the deadline, not on it. HMRC’s online services occasionally experience high demand around January and March. A test submission also confirms your software is correctly configured for iXBRL tagging before it matters.

When should you hire an accountant?

DIY filing is legally permitted for both sole traders and limited companies. Whether it is worth the effort is a different question.

Triggers that make professional help worth the cost:

• Your company files a CT600 with iXBRL-tagged accounts and computations
• You are newly registered for MTD and unsure which software qualifies
• You have overseas income, capital gains, or R&D relief claims
• HMRC has opened an enquiry or sent a compliance check letter
• You are spending more than a day per month on bookkeeping and tax admin
• You have employees and are running payroll alongside VAT and Corporation Tax

What an accountant does for you:

• Prepares statutory accounts to the correct accounting standard
• Computes Corporation Tax, applies reliefs, and completes the CT600
• Tags and files accounts in iXBRL format
• Submits Self Assessment returns and calculates payments on account
• Manages VAT returns and MTD compliance
• Runs payroll and handles RTI submissions
• Advises on cashflow planning around tax payment dates

Concorde Company Solutions Limited is the leading accountancy practice in Garforth, Leeds, with a reputation built on fixed-fee transparency and personal service. The team handles the full compliance cycle for sole traders, partnerships, and limited companies, from bookkeeping through to CT600 submission and beyond. For businesses in Leeds, Garforth, and Sherburn in Elmet, Concorde offers local expertise that national online services simply cannot replicate.

Filing taxes when your business has overseas income or operations

UK-resident companies pay Corporation Tax on worldwide profits. Sole traders resident in the UK pay Income Tax on worldwide income. The filing mechanics are the same, but the calculations become more complex.

Double taxation relief prevents the same income being taxed twice. If you have paid tax on overseas income in another country, you can usually claim relief against your UK tax liability, either through a double taxation treaty or unilateral relief. The relief is claimed on the CT600 (for companies) or through supplementary pages on the SA100 (for individuals).

Transfer pricing applies to transactions between connected parties in different countries. If your company trades with a related overseas entity, HMRC expects those transactions to be priced at arm’s length. This is primarily a concern for larger groups, but smaller companies with overseas subsidiaries or parent companies should take advice.

Permanent establishment is the concept HMRC uses to determine whether an overseas business has a taxable presence in the UK. If a foreign company has a fixed place of business or a dependent agent in the UK, it may owe UK Corporation Tax on profits attributable to that presence.

For sole traders with overseas clients, the income is simply reported on the SA103 as trading income. Foreign tax paid can be credited against the UK liability. Keep records of foreign invoices, exchange rates used, and any tax withheld at source.

Common tax reliefs and credits available to businesses

Reliefs reduce your tax bill, and many businesses claim less than they are entitled to simply because they are unaware of what is available.

Annual Investment Allowance (AIA): Allows businesses to deduct the full cost of qualifying plant and machinery in the year of purchase, up to the current limit. This covers most equipment, tools, and commercial vehicles. It applies to both sole traders and limited companies.

Research and Development (R&D) Relief: Companies that spend money developing new products, processes, or software may qualify for R&D relief, which either reduces Corporation Tax or generates a payable credit. The scheme was reformed in 2023 and 2024; the current merged scheme applies to most companies from April 2024.

Capital Allowances: Where AIA does not apply (or is exhausted), writing-down allowances reduce the value of assets over time, generating a deduction each year.

Employment Allowance: Reduces an employer’s National Insurance liability by up to £10,500 per tax year (from April 2025). Most small employers qualify; companies where the sole employee is also a director do not.

Creative Industry Tax Reliefs: Film, television, animation, video games, and theatre productions can claim enhanced deductions or credits. These are specialist reliefs with specific eligibility criteria.

Calculating which reliefs apply and how to claim them correctly is one of the clearest cases for professional help. A missed R&D claim or an incorrectly calculated AIA can mean paying significantly more tax than necessary.

How tax works for employee benefits and dividends

Two areas that consistently trip up small company directors are benefits in kind and dividend income. Both have their own reporting requirements on top of the standard returns.

Benefits in kind are non-cash perks provided to employees or directors: company cars, private medical insurance, interest-free loans above £10,000, and similar items. They must be reported to HMRC annually on a P11D form (or via payroll if the benefit is payrolled). The employer also pays Class 1A National Insurance on the value of the benefit, due by 19 July following the tax year end.

From April 2026, payrolling benefits in kind becomes mandatory for most employers, replacing the P11D process. If you currently submit P11Ds, check GOV.UK’s guidance on the transition timeline and register for payrolling before the deadline.

Dividends are a common way for limited company directors to extract profit tax-efficiently. They are not subject to National Insurance, but they are taxable as dividend income on the director’s Self Assessment return.

Dividends can only be paid from retained profits.

For a full breakdown of how to calculate your tax position as a director, the business tax calculation guide from Concorde Company Solutions Limited is a practical starting point.

How to prepare for an HMRC tax investigation or audit

HMRC opens enquiries for two reasons: random selection and specific risk indicators. Either way, the process is the same, and preparation makes an enormous difference.

What triggers an enquiry: Significant year-on-year profit fluctuations, expenses that appear high relative to turnover, inconsistencies between VAT returns and Self Assessment figures, or late or amended returns. Random enquiries also occur regardless of compliance history.

What HMRC can ask for: During a compliance check, HMRC can request business records, bank statements, invoices, contracts, and correspondence. They can go back up to four years for innocent errors, six years for careless errors, and twenty years for deliberate non-compliance.

How to prepare:

• Keep records for the full statutory period (five years for sole traders, six years for companies).
• Reconcile your bank statements to your accounts every month, not just at year-end.
• Retain evidence for every expense claim, including mileage logs and receipts for cash purchases.
• If HMRC contacts you, respond promptly and do not ignore letters.
• Appoint a professional representative early. An accountant or tax adviser can communicate with HMRC on your behalf, which reduces the risk of inadvertent admissions and keeps the process structured.

Concorde Company Solutions Limited supports clients through HMRC enquiries, from initial correspondence through to resolution. Having a professional handle the communication means you can focus on running your business while the compliance side is managed correctly.

An accountant’s perspective on filing business taxes

The most consistent mistake I see is business owners treating tax as a once-a-year event. By the time January arrives, the records are incomplete, the bank account has not been reconciled since March, and the filing becomes a scramble. The tax bill then arrives as a surprise rather than a planned expense.

The businesses that handle this well do two things differently. They reconcile their bookkeeping monthly, even if it takes only an hour. And they set aside a percentage of every invoice payment into a separate tax account, so the money is there when HMRC asks for it. Neither of these requires an accountant to implement, but both make the accountant’s job faster and cheaper when they do get involved.

On HMRC enquiries: the instinct to handle it yourself is understandable, but it is rarely the right call. HMRC enquiry officers are experienced at asking questions that seem straightforward but carry significant implications. A professional representative knows which questions require a direct answer and which warrant a more considered response.

Aligning your accounting period end with your quietest business month is a small structural decision that pays dividends every year. It gives you time to gather records, review the year, and plan the tax payment before the January rush hits.

Concorde Company Solutions Limited: tax filing support for UK businesses

Filing business taxes accurately takes time, technical knowledge, and an understanding of which reliefs and obligations apply to your specific situation. Concorde Company Solutions Limited, the number-one accountancy practice in Garforth, Leeds, removes that burden entirely.

The firm handles Corporation Tax return preparation, Self Assessment filing, VAT return submission, payroll management, bookkeeping, and iXBRL-compliant accounts for sole traders, partnerships, and limited companies across Leeds, Garforth, and Sherburn in Elmet. Fixed-fee pricing means no billing surprises, and the team’s MTD and iXBRL experience means your returns are filed correctly the first time.

Whether you need a one-off review of your tax position or ongoing monthly support, Concorde Company Solutions Limited offers a 2026 compliance guide and a straightforward route to getting your returns in order. Contact the team today to book a discovery call and find out how much time and money a dedicated local accountant can save you.

Sources

The links below are the authoritative starting points for registration, filing, and compliance. Bookmark the ones relevant to your business type.

• Gov
• Self-employment (full) notes (2026)
• Gov

This article is general information, not a substitute for advice from a qualified financial advisor. Consult a qualified financial professional about your own circumstances before acting on anything here.

Recommended

• Tax returns in the UK: your 2026 compliance guide – concordecompanysolutions.io
• What is self assessment? Your 2026 UK filing guide – concordecompanysolutions.io
• How to Calculate Business Taxes for UK Companies Easily
• Small Business Tax Deadlines 2025: Stay Compliant Easily