Self Assessment Tax Return for Tradespeople UK — Complete Guide (2026)

If you work for yourself as a tradesperson in the UK — whether you're a sole trader, a CIS subcontractor, or a limited company director — you almost certainly need to file a Self Assessment tax return each year. Yet for many tradespeople it remains one of the most dreaded admin tasks of the year: confusing deadlines, unclear rules about what you can claim, and the ever-present fear of getting it wrong. This guide cuts through the noise and gives you exactly what you need to know.

Who needs to file Self Assessment

HMRC requires you to file a Self Assessment tax return if any of the following apply to you in a given tax year:

• You are a sole trader and your gross self-employment income was more than £1,000
• You are a CIS subcontractor who had tax deducted at source by contractors
• You are a director of a limited company (even if your only income is a salary through PAYE)
• You had rental income from a property
• Your total income exceeded £100,000
• You received income from savings, investments or dividends not already taxed at source
• You or your partner received Child Benefit and your income was over £60,000 (the High Income Child Benefit Charge applies)

The £1,000 threshold is called the trading allowance. If your gross income from self-employment is below that figure, you do not need to declare it. But above £1,000, you must register and file — regardless of whether you actually owe any tax after expenses are deducted.

Registering for Self Assessment

If you're new to self-employment or have not filed before, you need to tell HMRC you exist before you can file. Registration is done online at gov.uk and takes around 20 minutes. You'll need a Government Gateway account (create one if you don't have one) and your National Insurance number.

Once registered, HMRC will send your Unique Taxpayer Reference (UTR) number by post within 10 working days. You cannot file without it. HMRC will also set up your online Self Assessment account, through which you'll file each year.

The deadline for registering is 5 October following the end of the tax year in which you became self-employed. The UK tax year runs from 6 April to 5 April. So if you started working for yourself in May 2025, you have until 5 October 2025 to register for Self Assessment. Miss this deadline and you may face a penalty — even if you owe no tax.

Key dates and deadlines

The Self Assessment calendar has several dates that matter. Get these wrong and you'll face automatic penalties before HMRC has even looked at your return.

• 5 October — deadline to register for Self Assessment if you're newly self-employed
• 31 October — deadline for paper tax returns (most tradespeople file online and can ignore this)
• 31 January — deadline for online tax returns AND for paying any tax owed, including your first payment on account for the following year
• 31 July — deadline for the second payment on account (see below)

The tax year runs from 6 April to 5 April. So the tax return you file by 31 January 2027 covers the period 6 April 2025 to 5 April 2026 (the 2025–26 tax year).

What income to declare

Your Self Assessment return must include all sources of income, not just your trade earnings. The main categories for tradespeople are:

• Self-employment income — the total amount you invoiced and received from clients during the tax year
• CIS income — your gross CIS earnings (before deductions). The CIS deducted by contractors counts as a tax credit against your bill — you enter it in a separate box on the return
• Employment income — if you also worked PAYE during the year
• Rental income — income from letting property (after allowable property expenses)
• Savings interest — interest above your Personal Savings Allowance (£500 for basic rate taxpayers, £500 for higher rate)
• Dividends — if you run a limited company and pay yourself dividends, these are declared here

For CIS subcontractors, it's essential to declare your gross income (the amount before CIS was deducted), not the net amount you actually received. Underdeclaring by using the net figure is a common mistake that can lead to HMRC penalties.

Allowable expenses for tradespeople

Your taxable profit is your income minus your allowable business expenses. Getting your expenses right is the single biggest lever you have over your tax bill. The following are all allowable for most tradespeople:

• Tools and equipment — hand tools, power tools, test equipment, ladders. Items under £1,000 can usually be expensed immediately. Items over £1,000 are claimed via capital allowances (see below)
• Van and vehicle costs — you can claim actual costs (fuel, insurance, servicing, road tax, MOT, tyres) or use HMRC's flat rate: 45p per mile for the first 10,000 miles per year, then 25p per mile thereafter. Actual costs are usually better for vans; the flat rate suits lower mileage use of personal cars
• Fuel — claimable as part of actual vehicle costs, or implicitly included in the mileage flat rate
• Materials used in jobs — anything you buy and use on a client's job that you haven't charged back separately
• Workwear and PPE — hi-vis, steel-toe-cap boots, overalls, hard hats, gloves. General clothing (even if worn on site) is not allowable unless it's clearly a uniform or PPE
• Phone costs — the business proportion of your mobile bill; or the full cost of a dedicated business phone
• Insurance — public liability, tools and plant insurance, professional indemnity
• Accounting and bookkeeping fees — the cost of your accountant or any software you use to manage finances
• Premises and storage — rent on a yard, garage or workshop used exclusively for business; a proportion of home office costs if you work from home
• Training and courses — relevant training that maintains or improves skills for your existing trade (CSCS cards, first aid, specific product training). Training to enter a new trade is generally not allowable
• Subcontractor costs — payments to subbies you take on for specific jobs
• Marketing — website hosting, business cards, advertising costs

The golden rule: an expense must be wholly and exclusively for the purposes of your trade. Anything with a personal element — a vehicle used privately, a phone used personally — must be apportioned, and only the business proportion claimed.

Capital allowances for equipment

When you buy a significant piece of equipment — a scaffolding system, a laser level, a van, a compressor — you usually can't expense the full cost in the year of purchase through the normal expenses route. Instead, you claim the cost through capital allowances.

The most useful relief here is the Annual Investment Allowance (AIA), which lets you deduct the full cost of qualifying plant and machinery in the year you buy it. The AIA limit is currently £1,000,000 per year — far more than most sole traders will ever spend. In practice, this means almost any equipment purchase a tradesperson makes can be fully deducted in the year of purchase through the AIA.

To claim AIA, declare the asset in the capital allowances section of your Self Assessment return. You'll need to note the date of purchase, the item, and the cost. Keep your receipts — HMRC can and does ask for evidence.

Cars (as opposed to vans) are excluded from AIA and fall under separate writing down allowance rules. This is another reason why a van is often more tax-efficient than a car for tradespeople.

Payments on account explained

One of the most surprising things about Self Assessment is that in your second year of filing, you don't just pay your tax bill once — you pay it in three instalments spread across the year. This is called payments on account.

Payments on account are advance payments toward your next year's tax bill. HMRC assumes your income in the coming year will be similar to the current year, so it asks you to pay half your current tax bill in January and another half in July. Then in the following January, you pay the “balancing payment” (the difference between what you've paid on account and what you actually owe) plus the first payment on account for the year after that.

This catches many tradespeople off guard in their second year. Where year one requires one payment, year two suddenly requires two — the balancing payment for year one, plus the first on-account payment for year two. All due by 31 January.

If your income drops significantly in a year — due to illness, a slow patch or deliberate scaling back — you can apply to reduce your payments on account online through your HMRC account. Don't just stop paying; you need to formally request a reduction, otherwise interest will accrue on the unpaid amounts.

How to file your Self Assessment return

There are three main ways to file:

• HMRC's own online portal — log in at gov.uk/log-in-file-uk-tax-return. It walks you through each section step by step. Free, but requires you to understand what goes where
• Accounting software — platforms like Xero, QuickBooks and FreeAgent can file directly to HMRC via Making Tax Digital connections. Your income and expenses are already tracked throughout the year, so pulling the return together takes minutes
• An accountant — for complex situations (limited company income alongside self-employment, property income, capital gains), a qualified accountant is well worth the cost. Their fee is also a deductible business expense

Whichever method you choose, the process is the same: declare your income, deduct your allowable expenses, claim any capital allowances, enter any CIS deductions as tax credits, and HMRC calculates what you owe. You can check the calculation before you submit and save a draft to come back to.

Keeping good records

HMRC expects you to keep records that back up every figure in your tax return. For sole traders, you must keep records for at least 5 years and 10 months from the 31 January filing deadline for the relevant tax year. In practice, this means roughly 6 years from the end of the tax year in question.

The records HMRC expects you to keep include:

• Invoices and receipts for all business income
• Receipts for all business expenses
• CIS deduction statements from contractors
• Bank statements showing business transactions
• Mileage logs if claiming vehicle costs (date, journey purpose, miles)
• Purchase invoices for any capital equipment

Digital records are perfectly acceptable — photos of receipts, PDFs of invoices, exported bank statements. The key is that records are complete, organised and retrievable. HMRC can open an enquiry into any return up to 12 months after you file it, or longer if they suspect fraud. Having organised records means any enquiry is resolved quickly rather than becoming a drawn-out ordeal.

Common mistakes and penalties

HMRC's penalty regime is automatic and unsympathetic. The penalties for Self Assessment non-compliance stack up quickly:

• Late filing — £100 fixed penalty the day after the deadline, even if no tax is owed. After 3 months, a further £10 per day (up to £900). After 6 months, 5% of the tax due or £300 (whichever is higher)
• Late payment — interest at the HMRC rate (currently around 7.5%) from the day after the deadline. After 30 days, a 5% surcharge on the unpaid tax. After 6 months, another 5%. After 12 months, another 5%
• Inaccurate returns — if HMRC finds errors, penalties range from 0% (for innocent mistakes where you tell HMRC unprompted) to 30% of unpaid tax (for careless errors) to 100%+ for deliberate evasion

Beyond penalties, the most common costly mistakes tradespeople make are:

• Declaring net CIS income instead of gross income
• Forgetting to claim all allowable expenses (leaving money on the table)
• Claiming personal costs as business expenses (the reverse problem, which HMRC targets in enquiries)
• Not keeping mileage logs, then being unable to substantiate vehicle cost claims
• Ignoring payments on account until the bill arrives, then not having the cash to pay
• Missing the registration deadline when starting out, then facing a penalty before even filing the first return

The good news: all of these are avoidable with basic organisation and awareness of the rules. A good accounting system, consistent record-keeping, and filing well before the deadline are enough to steer clear of every penalty on the list.