Self Assessment Deadline Guide for UK Tradespeople

If you work for yourself as a builder, electrician, plumber, decorator, labourer or other tradesperson, Self Assessment is how you tell HMRC about your income and pay the tax you owe.

The deadlines are predictable, but leaving everything until January can make the process stressful. This guide explains the key dates, what records you need, how CIS deductions fit in and what happens if you miss a deadline.

The Main Self Assessment Deadlines

For most sole traders, the important dates are:

1. 5 October after the end of the tax year: deadline to tell HMRC you need to file a tax return if you are newly self-employed and have not already registered.
2. 31 October after the end of the tax year: deadline for a paper tax return.
3. 31 January after the end of the tax year: deadline for an online tax return and payment of tax owed, including the first payment on account where applicable.
4. 31 July: deadline for the second payment on account where applicable.

The UK tax year runs from 6 April to the following 5 April. For the 2025/26 tax year, which ends on 5 April 2026, your online return and any tax due are normally due by 31 January 2027.

For the 2026/27 tax year, ending 5 April 2027, the online return and payment deadline is 31 January 2028.

Always check the latest dates and your personal HMRC account, especially if a deadline falls on a weekend or bank holiday.

Who Needs to File a Tax Return?

You will usually need to register for Self Assessment and file a tax return if you are self-employed and your gross trading income was more than £1,000 in the tax year. This £1,000 figure is the trading allowance threshold, not your profit.

You may also need to file if you have other taxable income, are a partner in a business, have untaxed income or HMRC tells you to submit a return.

If you only started trading recently, do not wait until the tax return deadline to think about registration. Register with HMRC as soon as you know you need to file, and remember the 5 October notification deadline after the end of the relevant tax year.

What You Need to Include

Your tax return normally covers your total income and allowable business expenses for the tax year. Keep the following information ready:

1. Total sales and income from customers
2. Invoices and payment records
3. Allowable expenses, such as tools, materials, insurance, software and business travel
4. Vehicle mileage or actual vehicle-cost records, depending on the method you use
5. Bank interest and other taxable income
6. Pension contributions and relevant reliefs
7. CIS deduction statements from contractors
8. Details of payments on account already made
9. Any student loan or other information requested by HMRC

You do not normally send receipts with the return, but you must keep records in case HMRC asks to see evidence.

How CIS Deductions Affect Your Tax Return

If you work as a CIS subcontractor, the contractor may deduct tax from your labour payments before paying you. A registered subcontractor commonly has 20% deducted, while an unregistered subcontractor may have 30% deducted. Gross payment status means the contractor does not deduct CIS tax.

CIS deductions are advance payments towards your tax and National Insurance. They are not automatically your final bill.

For example:

1. You invoice £40,000 in labour and materials during the year.
2. Contractors deduct £6,000 through CIS.
3. You have £10,000 of allowable business expenses.
4. Your taxable profit is calculated from your income and allowable costs.
5. The £6,000 CIS deduction is then credited against the tax and National Insurance calculated on your return.

If your deductions are higher than your final liability, HMRC may owe you a repayment. If they are lower, you must pay the difference by the deadline. Keep every payment and deduction statement — a bank payment alone does not always show the CIS calculation clearly.

What Counts as an Allowable Expense?

An allowable expense must be incurred wholly and exclusively for your business, subject to the specific rules for that type of cost. Common examples for tradespeople include:

1. Tools, equipment repairs and replacement items
2. Materials bought for customer jobs
3. Public liability and professional insurance
4. Accountancy and business software fees
5. Advertising, website and trade directory costs
6. Business mileage, parking and qualifying travel
7. Protective clothing and safety equipment
8. The business proportion of phone and internet costs
9. Certain costs of working from home

If a cost is partly personal, claim only the reasonable business proportion. Ordinary everyday clothing is generally not allowable just because you wear it at work, while protective clothing and safety equipment are more straightforward.

Keep your receipts and write down the business reason for anything that might not be obvious from the receipt itself.

Payments on Account: The Surprise January Bill

If your tax bill is above the relevant threshold, HMRC may ask you to make payments on account for the following tax year. Each payment is normally half of your previous year's tax bill, due on 31 January and 31 July.

That can make the first January payment feel much larger than expected. It may include:

1. The balance of tax and National Insurance for the previous year
2. Your first payment on account for the current year

The July payment is normally the second payment on account. If your income is expected to fall substantially, you may be able to apply to reduce the payments, but do not reduce them without a reasonable basis — interest can apply if the reduction is too low.

A Simple Preparation Timetable

During the tax year

Save invoices, receipts, bank records, mileage logs and CIS statements as you go. Keep business and personal spending separate where possible.

After 5 April

Close your records for the tax year. Add up income, check expense categories, confirm CIS deductions and compare your figures against bank statements.

By summer

Estimate your profit and likely tax. This gives you time to put money aside and ask an accountant about anything unusual.

By autumn

Aim to complete your online return well before 31 January. Filing early shows you what you owe and avoids a last-minute scramble.

Before 31 January

Submit the return, check the payment reference and pay the tax due. Leave time for bank processing and do not assume a payment made late on the day has arrived with HMRC.

What Happens If You Miss the Deadline?

HMRC can charge an automatic £100 late-filing penalty when a return is submitted late, even if no tax is owed. Further penalties can apply if the return remains outstanding for longer, and interest may be charged on late tax payments.

If you have missed a deadline, file as soon as possible and pay what you can. If you have a genuine reasonable excuse, explain it to HMRC and keep evidence. Do not ignore letters or wait for the next tax year to sort it out.

How to Make Self Assessment Easier

1. Use a separate business bank account.
2. Record income and expenses every week rather than once a year.
3. Keep CIS statements in one clearly labelled folder.
4. Number invoices consistently and mark when they are paid.
5. Put a percentage of every payment aside for tax and National Insurance.
6. Review your estimated profit monthly.
7. Set a personal reminder several weeks before each deadline.

Invoice Hero helps you keep customer details, invoices and payment status organised throughout the year. Combine that with a simple expense-recording routine and you will have much cleaner information when it is time to complete Self Assessment. Try Invoice Hero free at invoicehero.co.uk/register.

FAQ

When is the Self Assessment deadline for UK tradespeople? For most sole traders, the online return and tax payment deadline is 31 January after the end of the tax year. A second payment on account may be due on 31 July.

Do CIS subcontractors still need to file a tax return? Usually, yes. CIS deductions are advance payments and must be included when working out your final tax and National Insurance position.

Can I claim tools and materials on Self Assessment? You can generally claim costs incurred wholly and exclusively for the business, provided they meet HMRC's rules. Keep receipts and records showing the business purpose.

Do I need to send receipts to HMRC? You normally enter totals on the return rather than sending every receipt, but you must keep supporting records and produce them if HMRC asks.

What if I cannot pay my tax bill? File the return on time even if you cannot pay in full. Contact HMRC promptly to discuss payment options rather than ignoring the bill.

How long should I keep Self Assessment records? Keep records for at least five years after the 31 January filing deadline for the relevant tax year. Check current HMRC guidance if your circumstances or filing date are unusual.

This article provides general information for UK tradespeople, contractors and sole traders. Tax rules and thresholds can change, and your circumstances may be different. Check current HMRC guidance or speak to a qualified accountant.