Self Assessment for Tradespeople — What to Do If You've Never Filed Before

Going self-employed is straightforward enough. You get the work, you do the job, you invoice. Then January arrives and someone mentions Self Assessment and suddenly there's a sinking feeling that you've been doing something wrong all year.

You probably haven't. But if you've never filed before, here's exactly what it involves and how to get sorted.

Who needs to file?

If you're self-employed and earning more than £1,000 in a tax year, you need to file a Self Assessment return. That covers sole traders, subcontractors under CIS, and anyone working for themselves rather than on a PAYE payroll.

If you've been working under CIS and your contractor has been deducting 20% or 30% from your payments, you still need to file. Those deductions are advance payments toward your tax bill — they don't replace the return.

Registering for Self Assessment

If you've never registered, do it now at gov.uk/register-for-self-assessment. You'll get a Unique Taxpayer Reference (UTR) in the post within about 10 working days. You need that UTR before you can file anything.

Register as soon as you go self-employed. HMRC want you registered by 5 October following the end of the tax year in which you started trading. Miss that and you can get a penalty even before you've filed anything.

The tax year and deadlines The UK tax year runs 6 April to 5 April. So the 2025/26 tax year runs from 6 April 2025 to 5 April 2026.

Key deadlines: 5 October — register for Self Assessment if you're newly self-employed 31 January — online return filing deadline and payment deadline 31 July — payment on account deadline (second payment, if applicable)

Miss 31 January and you get an automatic £100 penalty, even if you don't owe any tax.

What information do you need?

Before you sit down to file, you need: Total income from self-employment (all invoices paid in the tax year, not raised) Total allowable expenses (tools, van, insurance, phone, accountant fees etc) CIS deduction statements from your contractors — these show how much was deducted on your behalf Any other income — PAYE jobs, rental income, savings interest Your UTR and National Insurance number Your Government Gateway login

What does the return actually cover?

You're declaring your income, deducting your allowable expenses, and arriving at a taxable profit. Tax is then calculated on that profit. Any CIS deductions you've had are credited against what you owe.

If your CIS deductions are more than your tax bill — which happens more often than people realise, especially if you've had a quieter year or claimed all your expenses — HMRC will refund the difference.

Payment on account — the thing that catches everyone out

In your first year of Self Assessment, many people get a shock. HMRC don't just ask you to pay what you owe for the year — they also ask for a payment on account toward next year's bill. It's 50% of your current year's tax bill, paid at the same time as the return, and another 50% in July.

So if your first tax bill is £4,000, HMRC want £6,000 by 31 January — £4,000 for the year just gone and £2,000 toward the year in progress. That surprises a lot of first-time filers.

Set money aside as you go. A rough rule of thumb for sole traders is to set aside 25-30% of every payment you receive. It won't always be exactly right but it stops January being a disaster.

Do you need an accountant?

Not legally, but for most tradespeople it's worth it. A decent accountant will find expenses you haven't thought of, handle the return properly, and usually save you more than they cost. Accountant fees are themselves a claimable expense.

If your affairs are genuinely simple — one income stream, straightforward expenses, no VAT — filing yourself through the HMRC website is manageable. But most tradespeople with CIS, VAT, or multiple income streams benefit from professional help.

Dayrates keeps all your invoices, expenses and CIS records in one place and produces a monthly summary your accountant can work straight from. Less time for them means a lower bill for you.

The honest version Self Assessment sounds worse than it is. It's mostly just telling HMRC what you earned, what you spent, and working out what you owe. Get registered, keep records as you go, set money aside, and either file it yourself or give an accountant clean records to work from. That's really all there is to it.