How to Do a Self Assessment Tax Return as a Tradesperson
If you’re self-employed as a tradesperson in the UK, you need to complete a Self Assessment tax return every year. Getting it wrong or missing the deadline can result in automatic fines from HMRC. The good news: once you understand the process and have your records in order, it’s a manageable annual task rather than something to dread.
Who Needs to Complete a Self Assessment Tax Return?
As a self-employed tradesperson – sole trader or partner in a business – you need to file a Self Assessment return if you earn more than £1,000 from self-employment in a tax year. You may also need to file if you have income from multiple sources, earn over £100,000 in total income, or have untaxed income such as rental income or savings interest.
Key Dates for 2025/26
The UK tax year runs 6th April to 5th April the following year. The 2025/26 return covers income earned 6 April 2025 to 5 April 2026.
Step-by-Step: How to File Your Self Assessment
Step 1
Register for Self Assessment
If you’ve never filed before, register with HMRC at gov.uk/register-for-self-assessment. HMRC will post you a Unique Taxpayer Reference (UTR) 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 Records Throughout the Year
The easiest way to make Self Assessment straightforward is to keep records continuously rather than scrambling in January. You need to track: all income received, all business expenses (materials, fuel, tools, insurance, phone, software), bank statements, receipts for significant purchases, and mileage logs if claiming vehicle costs.
💡 Good accounting software like Xero or QuickBooks pulls in bank transactions automatically, categorises them, and keeps everything organised – so your figures are ready to go when January comes.
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, create one – have your UTR number ready. Select “Complete your tax return” for the relevant tax year.
Step 4
Fill In the Main Tax Return (SA100)
The SA100 covers your personal details, income from all sources, and any tax reliefs you’re claiming. Work through each section – most of it is straightforward: your name, address, NI number, and a summary of income.
Step 5
Fill In the Self-Employment Supplement (SA103)
As a self-employed tradesperson, you also need to complete the SA103 – where you declare your business income and expenses.
Business income: enter your total turnover – every penny received from customers before expenses.
Allowable expenses: claim the costs of running your business. Common allowable expenses for tradespeople include materials and stock, tools and equipment, van and fuel costs, business insurance, workwear and PPE, phone and broadband, accounting and software fees, and training.
Net profit: HMRC calculates this 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 Tax Reliefs
Everyone has a Personal Allowance – the amount you can earn before paying income tax. For 2025/26 and 2026/27 this is £12,570, frozen until April 2031. If your taxable profit is below this, you won’t owe income tax (though you may still owe National Insurance).
Other reliefs worth knowing: the Annual Investment Allowance lets you deduct the full cost of qualifying equipment purchases in the year of purchase – particularly useful for tradespeople buying vehicles or plant machinery.
Step 7
National Insurance Contributions
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. Below that threshold, you can choose to pay voluntary Class 2 at £3.65/week to protect your pension record.
Class 4 NIC: 6% on profits between £12,570 and £50,270, and 2% above that. Calculated automatically on your return.
Step 8
Review and Submit
Before submitting, check: all income is included and accurate; all expenses are correctly categorised; your bank details are correct for any refund; the figures match your accounting records. Then submit. HMRC will calculate your total bill and show you the payment deadline.
Step 9
Pay Your Tax Bill
Tax owed must be paid by 31 January. You can pay via online banking, debit card through the HMRC website, or Direct Debit. 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.
⚠ Payments on account: if your tax bill is over £1,000, HMRC will also ask for advance payments towards the following year’s bill – 50% in January and 50% in July. This catches many tradespeople off guard in their first year – effectively paying 150% of their tax bill in a single January. Budget for it in advance.
Tips for Making Self Assessment Easier
Use accounting software
Xero or QuickBooks will have most figures ready to go and can pull directly from your bank. Some software submits directly to HMRC.
File early, not in January
The portal opens in April. Filing early means knowing your tax bill months ahead – giving you time to save for it rather than scrambling.
Claim every allowable expense
Most tradespeople underclaim. Every allowable expense directly reduces your tax bill – see our full expenses guide for everything you can claim.
Set money aside throughout the year
A simple rule: set aside 25–30% of every payment into a separate account for tax. You’ll never be caught short in January.
Consider an accountant
A good accountant costs £300–£600/year and typically saves significantly more than that through correctly claimed expenses and tax planning. 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 submissions rather than just an annual return. This extends to £30,000 income from April 2027. If your turnover is approaching either threshold, get MTD-compatible software in place now.
Try Tradify Free for 14 Days →Frequently Asked Questions
Register for Self Assessment at gov.uk/register-for-self-assessment if you haven’t already – you’ll receive a UTR (Unique Taxpayer Reference) by post. Keep records of all income and expenses throughout the year. Log in to your HMRC Government Gateway account and complete the SA100 main form plus the SA103 self-employment supplement, entering your total income and allowable business expenses. Submit before 31 January for the online return. HMRC calculates your tax and NI bill automatically.
The main allowable expenses for tradespeople on a Self Assessment return include: materials and stock used on jobs; tools and equipment; van or vehicle costs (either actual costs or flat-rate mileage at 45p per mile for the first 10,000 miles); fuel; business insurance including public liability; workwear and PPE; phone and broadband used for business; accounting and software fees; and professional training and development. Any cost incurred wholly and exclusively for the purpose of your business is potentially allowable.
The online filing and payment deadline for the 2025/26 tax return (covering income from 6 April 2025 to 5 April 2026) is 31 January 2027. The deadline to register for Self Assessment for the first time for this tax year is 5 October 2026. The paper return deadline is 31 October 2026. Filing early is strongly recommended – the portal opens in April and early filing means knowing your bill months before payment is due.
If your Self Assessment tax bill is over £1,000 and less than 80% of your tax was collected at source, HMRC requires you to make advance payments towards the following year’s bill. These are called payments on account – two instalments of 50% of your previous year’s bill, paid in January and July. In your first year of Self Assessment, this means the January payment effectively covers 150% of your tax bill – the current year’s bill plus the first payment on account for next year. Budget for this well in advance.
No – you can file Self Assessment yourself using HMRC’s online portal or accounting software. Many tradespeople handle their own returns successfully. However, a good accountant costs £300–£600/year and typically saves more than that through correctly claimed expenses, tax reliefs you may not have known about, and avoiding errors that can trigger HMRC enquiries. If your income is above £50,000, you have complex expenses, or you are approaching the Making Tax Digital thresholds, getting professional help is strongly recommended.
Self-employed tradespeople pay Class 4 National Insurance on their profits – 6% on profits between £12,570 and £50,270, and 2% above that. Class 2 NIC is no longer compulsory: if your profits are above £7,105 for 2026/27, you automatically receive a qualifying year towards your State Pension without paying anything extra. 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. Both are calculated automatically on your Self Assessment return.
This guide provides general information only and does not constitute tax advice. Tax rules change and individual circumstances vary – always check current rates at GOV.UK or speak to a qualified accountant for advice specific to your situation. Some links on this page are affiliate links; if you sign up through them we may earn a commission at no extra cost to you.