A contractor’s tax return is rarely difficult because of one complicated calculation. More often, problems arise because income has come through several routes, receipts have not been kept consistently, or a deadline has been left until the last week of January. A clear contractor tax return guide helps you bring those moving parts together before they become a source of stress.
Whether you work as a sole trader, through a limited company or under the Construction Industry Scheme (CIS), the right return and the right supporting records depend on how you operate. Getting this distinction right is the starting point for accurate reporting and sensible tax planning.
Contractor tax return guide: start with your business structure
The phrase “contractor tax return” can mean different things. Your obligations are shaped by your trading structure, not simply by the work you do.
A sole trader normally reports business income and allowable expenses through Self Assessment. You will complete the self-employment section of the return, alongside any other income you receive, such as employment income, rental profits, bank interest or dividends.
If you run a limited company, there are usually two separate responsibilities. The company submits annual accounts and a Company Tax Return, then pays Corporation Tax on its profits. As a director, you may also need to submit a personal Self Assessment tax return to report salary, dividends and any other taxable income. Treating the company’s money and your personal money as separate is essential, both for compliance and for understanding what tax is due.
CIS contractors and subcontractors have another layer to consider. If tax has been deducted from your payments under CIS, this is not a final tax bill. It is generally a payment towards the tax and National Insurance due on your profits. Keep every payment and deduction statement, as these figures need to be claimed correctly on your Self Assessment return.
Your position may also be affected by off-payroll working rules, commonly called IR35. Where an engagement is inside IR35, tax may already be deducted through PAYE. This does not automatically remove the need for a tax return, particularly if you have other income or HMRC has asked you to file one. The treatment depends on the engagement and the contract in place.
Know the tax return deadlines before they become urgent
The UK tax year runs from 6 April to 5 April. For the tax year ending 5 April, an online Self Assessment tax return is normally due by 31 January of the following year. Any balancing tax payment is usually due on the same date.
If you are newly self-employed and have not previously completed a return, you generally need to tell HMRC by 5 October following the end of the tax year in which you started. Leaving registration late can make an otherwise manageable filing process much harder.
There may also be payments on account. These are advance payments towards your next year’s tax bill, normally due on 31 January and 31 July. They commonly apply where your Self Assessment bill is more than £1,000 and less than 80% of your tax was collected at source. This can be a surprise in a contractor’s first profitable year because the January payment may include tax for the previous year and the first advance payment for the next one.
A reduced payment on account can be requested where you reasonably expect your income to fall. However, reducing it without a sound basis can lead to interest if the final bill proves higher. A forecast based on current contracts, expected costs and likely gaps between projects is far safer than a guess.
For limited companies, deadlines are different. Company accounts are generally filed with Companies House nine months after the year end, while Corporation Tax is usually payable nine months and one day after the end of the accounting period. The Company Tax Return is normally due 12 months after that period ends. These dates can sit well outside the personal Self Assessment timetable, which is why a forward-looking calendar matters.
Build your return from reliable records
A tax return should be the final stage of your record-keeping, not the point at which you start searching through emails and bank statements. Regular bookkeeping gives you a clearer view of profit during the year and reduces the risk of omitted income or unsupported expense claims.
Keep a record of every invoice raised and every payment received. If you are VAT registered, make sure your VAT records agree with the sales figures used in your accounts and return. For CIS work, retain deduction statements and reconcile them to payments received.
For expenses, keep receipts, invoices and evidence of the business purpose. Digital copies are usually practical and easier to retrieve, provided they are clear and complete. A dedicated business bank account is particularly helpful, even for sole traders, because it reduces the work needed to separate business transactions from personal spending.
Contractors should normally retain records for at least five years after the 31 January submission deadline for the relevant tax year. Limited companies may have additional record-keeping obligations. Good records are not just for HMRC – they also make it easier to assess whether a contract is profitable, whether costs are rising and how much cash should be reserved for tax.
Claim expenses carefully, not aggressively
Allowable expenses can reduce taxable profit, but only where they meet the relevant rules. For a sole trader, costs generally need to be incurred wholly and exclusively for the business. For companies, the company must have paid the cost and there must be a legitimate business reason for the claim.
Common contractor costs may include accountancy fees, professional subscriptions, business insurance, software, equipment, advertising, phone costs and training that maintains or improves existing skills. The detail matters. Training to keep current in your established trade may be allowable, while training for a new trade or profession may not be.
Travel is one of the areas most likely to be misunderstood. Travel to a temporary workplace may be claimable, while ordinary commuting to a permanent workplace is usually not. The rules can be more complex for contractors working through a limited company, particularly where IR35 applies or a workplace becomes effectively permanent. Do not assume that a journey is allowable simply because it relates to a client.
If you work from home, you may be able to claim a reasonable proportion of household costs or use a simplified method where appropriate. The best approach depends on your circumstances, the type of costs involved and how regularly you use your home for work. Claims should be fair, evidenced and proportionate.
Avoid treating every business-related purchase as automatically deductible. Clothing, meals and mixed personal-business costs are frequent areas of confusion. A clear explanation and supporting evidence are far more valuable than an inflated claim that creates risk later.
Check all income, not only invoices
Before submitting a return, reconcile your income to bank statements, accounting records, PAYE documents and CIS statements. This is especially important if you have moved between contracts, worked for several clients or received a mix of salary, dividends and self-employed income during the year.
If you are a company director, check that dividends have been properly declared and recorded. Dividends should not simply be treated as ad hoc withdrawals from the company account. If money has been taken in a different way, it may need to be reflected through payroll, expenses, a director’s loan account or another appropriate route.
Also include income that sits outside your main contracting work where required. This can include property income, savings interest, capital gains or overseas income. A tax return is a declaration of your overall relevant tax position, not only a report of one contract.
Put money aside throughout the year
Cash flow is often the real challenge for contractors. An apparently healthy bank balance can include VAT collected for HMRC, money needed for Corporation Tax or Income Tax, and funds required for future supplier costs or quieter periods.
A practical habit is to transfer a portion of each payment received into a separate tax savings account. The right percentage varies depending on your structure, profit level, VAT position, other income and whether you have payments on account. Reviewing this regularly is better than relying on a fixed rule of thumb.
Cloud accounting software can make this easier by keeping invoices, expenses, bank transactions and VAT information together. It can also provide a useful estimate of tax liabilities, although estimates should be reviewed alongside your wider circumstances rather than treated as a final figure.
When professional support makes a difference
A straightforward sole trader return may be manageable with organised records and a clear understanding of the rules. However, advice is particularly worthwhile when you have CIS deductions, limited company income, IR35 questions, multiple income sources, VAT, a director’s loan account or a growing business.
The value is not limited to submitting the form. A proactive accountant can help you plan for payments on account, identify legitimate reliefs, keep company and personal obligations aligned, and address questions before a deadline is close. For contractors who want clear guidance without unnecessary jargon, Coombs Chartered Accountants can provide that ongoing support.
The best time to prepare your return is when the information is still fresh and the choices are still yours. A short review of your records now can turn January from a deadline to fear into a routine part of running your contracting business.
