How to Do a Self Assessment Tax Return as a Tradesperson

Self Assessment Doesn’t Have to Be Something You Dread

If you’re self-employed as a tradesperson in the UK, you need to complete a Self Assessment tax return every year. It’s not optional – and getting it wrong or missing the deadline can result in fines from HMRC.

The good news is that Self Assessment is much more straightforward than most people think. Once you understand the process and have your records in order, it’s a manageable annual task rather than something to dread.

This guide walks you through exactly how to do a Self Assessment tax return as a tradesperson – step by step, in plain English, covering the 2025/26 tax year return due by 31 January 2027.

Who Needs to Complete a Self Assessment Tax Return?

As a self-employed tradesperson – whether you’re a sole trader or a partner in a business – you need to complete a Self Assessment tax return if you earn more than £1,000 from self-employment in a tax year.

You may also need to complete one if you:

• Have income from multiple sources
• Earn over £100,000 in total income
• Have untaxed income such as rental income or savings interest
• Are a company director

If you’re unsure whether you need to register, check the HMRC website or speak to an accountant.

Key Dates to Know

Missing HMRC deadlines results in automatic fines – so get these in your diary now.

• 5th October 2026 – deadline to register for Self Assessment for the 2025/26 tax year if you’re doing it for the first time
• 31st October 2026 – deadline for paper tax returns
• 31st January 2027 – deadline to file your online tax return and pay any tax owed for the 2025/26 tax year
• 31st July 2027 – deadline for your second payment on account if HMRC requires advance payments

The UK tax year runs from 6th April to 5th April the following year. So your 2025/26 tax return covers income earned between 6th April 2025 and 5th April 2026 – and must be filed online by 31st January 2027.

Step 1: Register for Self Assessment

If you’ve never filed a Self Assessment return before, you need to register with HMRC first.

Go to gov.uk/register-for-self-assessment and register as self-employed. HMRC will send you a Unique Taxpayer Reference – your UTR number – in the post within ten working days. You’ll need this to file your return.

Do this as soon as you start trading – don’t wait until October.

Step 2: Keep Your Records Throughout the Year

The easiest way to make Self Assessment straightforward is to keep accurate records throughout the year rather than trying to piece everything together in January.

What you need to keep records of:

• All income received – every job, every invoice paid
• All business expenses – materials, fuel, tools, insurance, phone bills, software subscriptions
• Bank statements
• Receipts for any significant purchases
• Mileage logs if you’re claiming vehicle expenses

Good accounting software makes this effortless. Xero and QuickBooks both pull in transactions from your bank automatically, categorise them, and keep everything organised throughout the year – so when January comes you’re not scrambling to find a year’s worth of receipts.

Step 3: Log In to HMRC Online Services

Go to gov.uk/log-in-file-self-assessment-tax-return and sign in with your Government Gateway account. If you don’t have one, you’ll need to create one – have your UTR number ready.

Once logged in, select “Complete your tax return” for the relevant tax year.

Step 4: Fill In the Main Tax Return – SA100

The main Self Assessment form is called the SA100. It covers your personal details, income from all sources, and any tax reliefs you’re claiming.

Work through each section carefully. Most of it will be straightforward – your name, address, National Insurance number, and a summary of your income.

Step 5: Fill In the Self-Employment Supplement – SA103

As a self-employed tradesperson, you’ll also need to complete the SA103 – the self-employment supplement. This is where you declare your business income and expenses.

What to include on your SA103:

Business Income

Enter your total turnover for the year – every penny you received from customers. This is your gross income before any expenses are deducted.

Allowable Expenses

This is where you reduce your tax bill by claiming the costs of running your business. Common allowable expenses for tradespeople include:

• Materials and stock used on jobs
• Tools and equipment
• Van or vehicle costs – either actual costs or a flat mileage rate
• Fuel
• Public liability and other business insurance
• Workwear and PPE
• Phone and broadband used for business
• Accounting and software fees
• Training and professional development

We cover allowable expenses in full detail in our guide to what expenses a tradesperson can claim – but the key principle is that any cost incurred wholly and exclusively for the purpose of your business is potentially allowable.

Net Profit

HMRC calculates your taxable profit by subtracting your allowable expenses from your total income. This is the figure your tax bill is based on.

Step 6: Claim Your Personal Allowance and Any Reliefs

Everyone in the UK has a Personal Allowance – the amount you can earn before paying income tax. For the 2025/26 and 2026/27 tax years this is £12,570, frozen at this level until April 2031.

If your taxable profit is below this figure, you won’t owe any income tax – though you may still owe National Insurance depending on your circumstances.

Other reliefs worth being aware of:

• Trading Allowance – if your income is under £1,000 you may be able to claim this instead of itemising expenses
• Annual Investment Allowance – allows you to deduct the full cost of qualifying equipment purchases in the year of purchase
• Marriage Allowance – if your partner earns less than the Personal Allowance they can transfer up to £1,260 of it to you

Step 7: National Insurance Contributions

As a self-employed tradesperson you pay National Insurance separately from income tax. This changed significantly in April 2024, so it’s worth knowing the current rules rather than what older guides may say.

• Class 2 NIC – no longer compulsory for most self-employed people. If your profits are above the Small Profits Threshold (£7,105 for 2026/27), you automatically get a qualifying year for your State Pension without paying anything. If your profits are below that threshold, you can choose to pay voluntary Class 2 at £3.65/week to protect your State Pension record.
• Class 4 NIC – a percentage of your profits above the threshold: 6% on profits between £12,570 and £50,270, and 2% above that.

These are calculated automatically when you complete your Self Assessment return and added to your total bill.

Step 8: Review and Submit

Before submitting, go through your return carefully and check:

• All income is included and accurate
• All expenses are correctly categorised and evidenced
• Your bank details are correct for any refund
• The figures on screen match your accounting records

Once you’re happy, submit the return. HMRC will calculate your tax bill and show you the total amount owed and the payment deadline.

Step 9: Pay Your Tax Bill

Tax owed must be paid by 31st January. You can pay via:

• Online banking or bank transfer
• Debit card through the HMRC website
• Direct Debit
• CHAPS for same-day payment if needed

Don’t miss this deadline. The penalty for late payment is 5% of the tax owed after 30 days, with further penalties at six and twelve months.

Payment on account. If your tax bill is over £1,000 and less than 80% of it was collected at source, HMRC will also ask you to make advance payments towards the following year’s bill – known as payments on account. These are split into two instalments, each worth 50% of your previous year’s bill, paid in January and July. This catches many tradespeople off guard in their first year of Self Assessment, since it effectively means paying 150% of your tax bill in that single January payment, so it’s worth being aware of and budgeting for in advance.

Tips for Making Self Assessment Easier

Use Accounting Software

Xero or QuickBooks will have most of the figures you need ready to go. Some software can even submit your return directly to HMRC.

Don’t Leave It Until January

The Self Assessment portal opens in April. Filing early means you know your tax bill months in advance – giving you time to save for it rather than scrambling in January.

Claim Every Allowable Expense

Most tradespeople underclaim on expenses. Make sure you’re claiming everything you’re entitled to – it directly reduces your tax bill.

Set Money Aside Throughout the Year

A simple rule of thumb is to set aside 25–30% of every payment you receive into a separate savings account for tax. This way you’re never caught short in January.

Consider an Accountant

For most tradespeople, a good accountant costs £300–600 per year and saves significantly more than that through legitimate tax savings, correctly claimed expenses, and peace of mind. If your accounts are getting complex, it’s money well spent.

A Note on Making Tax Digital

Making Tax Digital for Income Tax is now live for self-employed people and landlords with qualifying income above £50,000, requiring quarterly digital record-keeping rather than just an annual return. This threshold is extending to £30,000 from April 2027. If your turnover is approaching either threshold, it’s worth getting MTD-compatible software in place now rather than waiting until you’re mandated to use it.

The Bottom Line

Self Assessment doesn’t have to be stressful. Get registered early, keep good records throughout the year, claim every allowable expense, and file well before the January deadline.

The single biggest thing you can do to make Self Assessment easier is to use accounting software that keeps your records organised automatically. Xero is the strongest option for UK tradespeople – particularly if you’re already using Tradify for job management, as the two integrate seamlessly.

And if you’re not yet using Tradify to manage your quotes, jobs, and invoices – it’s the best starting point for getting your trade business running more efficiently.

Pricing: From ~£34/month per user. Free 14-day trial, no card required.

TradeStack HQ helps UK tradespeople find the best software and AI tools to run a smarter business. Browse our full blog for reviews, comparisons, and practical guides built for the trades.

This guide provides general information and does not constitute tax advice. Tax rules can change and individual circumstances vary – always check current rates at GOV.UK or speak to a qualified accountant for advice specific to your situation.

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