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. 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.
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 — deadline to register for Self Assessment if you’re doing it for the first time
- 31st January — deadline to file your online tax return and pay any tax owed for the previous tax year
- 31st July — 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 2024/25 tax return covers income earned between 6th April 2024 and 5th April 2025 — and must be filed by 31st January 2026.
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 January.
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 2024/25 tax year this is £12,570.
If your taxable profit is below this figure, you won’t owe any income tax — though you may still owe National Insurance.
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 some of it to you
Step 7: National Insurance Contributions
As a self-employed tradesperson you pay National Insurance separately from income tax.
- Class 2 NIC — a flat weekly rate, currently £3.45/week, paid if your profits exceed £12,570
- Class 4 NIC — a percentage of your profits above the threshold, currently 9% 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, 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 paid in January and July. This catches many tradespeople off guard in their first year of Self Assessment so it’s worth being aware of.
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.
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.
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.