Self-Assessment Tax Returns for Tradespeople: Allowable Expenses, Capital Allowances and Filing Deadlines

Quick Answer: Self-employed tradespeople file an annual Self-Assessment tax return covering the tax year 6 April to 5 April. Online filing deadline is 31 January after the end of the tax year. From April 2026, MTD-IT replaces the single annual return with quarterly updates plus a final declaration for those with self-employment turnover above £50,000 (£30,000 from April 2027). Allowable expenses include materials, tools, vehicle costs (mileage at 45p/mile for first 10,000 miles or actual costs), van loan interest, public liability insurance, accountancy fees, and a proportion of home office expenses. Capital allowances of 100% (Annual Investment Allowance up to £1m) cover most plant and tools.

Summary

Self-Assessment is the annual UK process by which self-employed tradespeople (and others) report income to HMRC and calculate tax owed. For a sole-trader plumber, electrician or builder, it's the single most important compliance event of the year — and from April 2026, the once-yearly cycle is being replaced by quarterly Making Tax Digital for Income Tax Self Assessment (MTD-IT) submissions for those above the £50k turnover threshold.

The mechanics are straightforward but the detail matters. Income is reported gross (before any expenses). Expenses are deducted to give taxable profit. Income tax is calculated on profit at progressive rates (20%, 40%, 45%) above the personal allowance. Class 2 National Insurance is a flat weekly contribution; Class 4 is a percentage of profit. CIS deductions (for trades operating under the Construction Industry Scheme) are reported and offset against the calculated tax bill.

The single biggest area of taxpayer error is allowable expenses — what counts and what doesn't. Materials, tools, vehicle running costs, public liability insurance, accountant fees, and home office costs are all allowable if "wholly and exclusively" for the business. Personal expenses are not allowable. Mixed-use items (mobile phone, vehicles used for both work and personal) need apportionment. Getting the apportionment wrong is a flag for HMRC enquiry.

Key Facts

• Tax year — 6 April to 5 April (UK fiscal year)
• Online Self-Assessment deadline — 31 January after end of tax year
• Paper Self-Assessment deadline — 31 October after end of tax year (less common)
• Self-Assessment registration deadline — 5 October after end of first tax year of trading
• Personal Allowance (2025/26) — £12,570 (tapers above £100k)
• Basic rate income tax — 20% on profit £12,571–£50,270
• Higher rate income tax — 40% on profit £50,271–£125,140
• Additional rate income tax — 45% on profit above £125,140
• Class 2 NI (2025/26) — £3.45/week (£179.40/year) if profit above Small Profits Threshold £6,725
• Class 4 NI (2025/26) — 6% on profit £12,571–£50,270, 2% above
• Payments on account — twice yearly (31 January, 31 July) — effectively half of last year's tax in advance
• Annual Investment Allowance (AIA) — 100% relief on qualifying capital expenditure up to £1,000,000
• Mileage allowance (cars/vans) — 45p/mile first 10,000 miles, 25p/mile thereafter
• Trading allowance — £1,000/year tax-free trading income (alternative to actual expenses)
• Cash basis vs accruals basis — both available; cash basis simpler for trades under £150k
• MTD-IT mandatory threshold (April 2026) — £50,000+ self-employment turnover
• MTD-IT mandatory threshold (April 2027) — £30,000+

Quick Reference Table

Detailed Guidance

When you must register for Self-Assessment

A sole-trader must register with HMRC by 5 October after the end of the first tax year of trading. So if you start trading in May 2025 (within the 2025/26 tax year ending 5 April 2026), you must register by 5 October 2026.

Registration is via the gov.uk website — typically takes 10–15 minutes. HMRC issues a Unique Taxpayer Reference (UTR) within 14 days; this is needed for all future filings.

Failure to register by the deadline triggers:

• Initial late notification penalty: 10% of net tax due
• Continued failure: increasing penalties up to 100% of tax due

For a tradesperson who turned a side gig into a full business, the registration deadline can sneak up. Set a calendar reminder for 5 October of any year you start trading.

Tax year and filing deadlines

The UK tax year runs 6 April to 5 April. So:

• 2025/26 tax year: 6 April 2025 – 5 April 2026
• Online filing deadline: 31 January 2027
• Paper filing deadline: 31 October 2026 (rarely used)

Filing late triggers:

• Initial £100 fine (regardless of amount due)
• After 3 months: £10/day for 90 days (max £900)
• After 6 months: £300 or 5% of tax due (whichever higher)
• After 12 months: another £300 or 5% (whichever higher)

Plus interest on tax paid late (currently around 7% per annum).

For most trades, the 31 January online deadline is the only date that matters.

Cash basis vs accruals basis

For trades with annual turnover under £150,000, there's a choice between:

Cash basis — income counted when cash received, expenses counted when paid. Simpler for sole traders. Aligns with bank reconciliation.

• Pros: Simple, intuitive, no need to value stock or unpaid invoices at year-end
• Cons: Limits on capital allowances (only £500/year vehicle interest), no losses carry-back

Accruals basis (traditional accounting) — income counted when invoice raised, expenses counted when incurred. Standard accounting basis.

• Pros: Better matching of income and expenses, full capital allowances and loss relief
• Cons: More complex, year-end stock-take needed if applicable

For most small UK trades, cash basis is the right choice. Switch to accruals once you're consistently above £150k turnover or once stock and unpaid invoices become significant at year-end.

Income reporting

Report income gross (before any deductions). For most trades:

• Customer payments — total received in the tax year
• Bank interest on business account — separate box on the return
• Other income (e.g. eBay sales of business assets) — declare appropriately

For CIS subcontractors:

• Gross pay (before CIS deduction) is the income
• CIS deducted is a tax already paid, claimed as a credit against the calculated tax bill

Allowable expenses — the detail

Wholly and exclusively is the test. An expense is allowable only if it's incurred wholly and exclusively for the business. Mixed-use expenses must be apportioned.

Materials — anything bought for resale to a customer (cement, copper pipe, tile adhesive) is fully allowable.

Tools and equipment — small items (screwdrivers, drills under £200) are typically claimed as expenses. Larger items (compressor, jet wash, table saw) are capital expenditure and claimed via Annual Investment Allowance (100% in year of purchase).

Vehicle costs — choose one of:

1. Actual costs: fuel, insurance, tax, MOT, servicing, repairs, depreciation/lease costs. Apportion if vehicle has personal use.
2. Mileage allowance: 45p/mile for first 10,000 business miles per tax year, 25p/mile thereafter. Simpler. No fuel/repair claim — the mileage covers it all.

For a van used 100% for business: actual costs typically more advantageous. For a car used 70% for business / 30% personal: mileage allowance often wins because of the apportionment hassle.

You can't switch between methods on the same vehicle in the same tax year, but you can switch when you change vehicle.

Insurance — public liability, tool insurance, professional indemnity, van insurance. 100% allowable if business-only; apportion if dual-use.

Trade subscriptions — Gas Safe, NICEIC, NAPIT, PCA, HETAS, etc. 100% allowable.

Office and home office costs:

• Simplified expenses (flat rate): £6/week (£312/year), no records needed. Suitable for most small trades.
• Actual costs: proportion of household bills (rent/mortgage interest, council tax, utilities) based on rooms used and time used. Better for trades with substantial home office use.

Telephone and internet — apportion based on business use percentage. Typical: 70% business / 30% personal for a working tradesperson's mobile.

Computer, printer, software — if used for business primarily, 100% allowable (or apportion). Subscription software (Xero, QuickBooks, Powered Now) is fully allowable as ongoing expense.

PPE and workwear — protective clothing (steel toe boots, hi-vis, hard hat) 100% allowable. Branded workwear with company logo 100% allowable. General clothing not allowable.

Subsistence — only when working away overnight. Lunch on a normal job site is not allowable (you'd eat anyway).

Bad debts — invoices written off as uncollectable. Allowable on accruals basis; not relevant on cash basis (you didn't count the income in the first place).

Bank charges — on business account, 100% allowable.

Accountant and bookkeeper fees — 100% allowable.

Capital allowances — Annual Investment Allowance

For larger purchases (van, plant, machinery), capital allowances replace expense claims:

• Annual Investment Allowance (AIA) — 100% deduction in year of purchase, up to £1,000,000 of qualifying expenditure. Suits virtually all small trades.
• Writing Down Allowance (WDA) — 18% per year on the reducing balance for items not claimed via AIA

For a van bought for £25,000 in the 2025/26 tax year, the full £25,000 can be deducted from profit via AIA in 2025/26 — typically saving £5,000–£10,000 of tax depending on profit band.

Cars are treated differently:

• Sole trader's own car: claim mileage allowance (45p/mile), no separate capital allowance
• Business-bought car: AIA available but only on the business-use proportion; lower CO2 emission cars get higher allowance

National Insurance contributions

For self-employed sole traders:

• Class 2 NI: £3.45/week (£179.40/year for 2025/26) if profit above Small Profits Threshold (£6,725). Pays for state pension entitlement.
• Class 4 NI: 6% on profit £12,571–£50,270, 2% on profit above £50,270.

Both are reported and paid via Self-Assessment. The annual NI contribution sits separate from the income tax calculation.

For directors of limited companies: Class 1 NI applies via PAYE on salary, no Class 2 or Class 4. Different mechanics entirely.

Payments on account — the cash flow surprise

If your tax bill (income tax + Class 4 NI) for a year exceeds £1,000, HMRC requires "payments on account" toward the next year's tax:

• 31 January: Pay balance for past tax year + first payment on account for current tax year (50% of past year's tax)
• 31 July: Second payment on account for current tax year (the other 50%)

This means the first year of self-employment is harder than steady-state — you pay one tax bill and immediately pay 50% toward the next year's. Cash flow planning matters.

For a tradesperson with £40k profit in year 1 (say £6,000 tax bill), the January payment is £6,000 + £3,000 on account = £9,000. The July payment is another £3,000. If year 2's tax bill is also £6,000, the situation stabilises.

MTD-IT — the April 2026 change

From April 2026, sole traders and landlords with self-employment + property turnover above £50,000 must:

• Keep digital records using compatible software
• Submit quarterly updates to HMRC (4 per year)
• Submit final declaration replacing the single annual return

The threshold drops to £30,000 from April 2027.

What changes:

• 4 submissions/year instead of 1 (more touch-points but each smaller)
• Digital record-keeping mandatory (no more shoebox of receipts)
• Software-based filing (no more HMRC online form direct entry)

What stays the same:

• Tax year still 6 April – 5 April
• Payment dates still 31 January and 31 July
• Allowable expenses rules unchanged
• Personal allowance, tax bands, NI rates unchanged

Trading allowance — £1,000 tax-free

The trading allowance allows £1,000 of self-employment income per tax year tax-free. Useful for:

• Side hustles producing under £1,000 income
• Avoidance of Self-Assessment if total trading income under £1,000

For a serious trade business, the trading allowance is irrelevant (income exceeds £1,000 by orders of magnitude). For a side gig (selling tools online, occasional weekend handyman work), the trading allowance can mean no Self-Assessment is needed at all if income stays under £1,000.

Common errors and HMRC enquiry triggers

The errors most likely to trigger an HMRC enquiry:

• Round-number expenses — claiming "£500 for tools" when records would show £487.32 — HMRC's algorithms flag suspiciously round numbers
• Implausible apportionment — claiming 95% business use of a family vehicle when school runs are obvious from address pattern
• Cash income under-reporting — HMRC has industry benchmarks for cash-heavy trades and flags returns that show suspiciously low cash income
• Missing income from third parties — bank deposits not matching declared income
• Expense-to-income ratio outside benchmark — HMRC has expected ranges for each trade

Best protection is to keep good records (digital, dated, evidenced), apply expenses honestly, and use software with bank-feed reconciliation.

Frequently Asked Questions

When do I have to file my Self-Assessment?

By 31 January following the end of the tax year. The 2025/26 tax year (ending 5 April 2026) must be filed online by 31 January 2027. Paper deadline is 31 October — rarely used. Late filing triggers an automatic £100 penalty plus escalating fees and interest.

What expenses can I claim as a self-employed tradesperson?

Materials for jobs, tools and equipment (via AIA capital allowances), vehicle costs (45p/mile or actual costs), insurance (public liability, tool, van), trade subscriptions, accountancy fees, mobile phone (business %), home office expenses (£6/week flat or actual %), PPE, software subscriptions, bank charges. Personal expenses (groceries, family holidays) and most general clothing are not allowable.

How does CIS work on my Self-Assessment?

CIS deductions taken from your gross pay by contractors are recorded as tax already paid. Report gross income (before CIS), claim allowable expenses, calculate the tax due, then offset CIS deductions taken at source. Most CIS subcontractors get a tax refund at year-end because the 20% deducted exceeds the actual tax due after expenses. The refund is paid by HMRC after the return is processed.

Should I use the trading allowance or claim actual expenses?

Use whichever gives the lower tax bill. The trading allowance gives a flat £1,000 deduction with no records needed. Actual expenses give the real total of allowable spending. For any serious trade business, actual expenses will far exceed £1,000 — claim them. The trading allowance is only useful for tiny side-hustles.

What changes when MTD-IT starts in April 2026?

If your self-employment turnover is above £50,000 (or £30,000 from April 2027), you'll submit 4 quarterly updates to HMRC plus a final declaration, replacing the single annual return. Records must be kept digitally in compatible software. Tax year, payment dates, allowable expense rules, and tax bands all stay the same. The change is the filing process, not the underlying tax.

Regulations & Standards

• The Income Tax (Trading and Other Income) Act 2005 — primary income tax legislation

• The Income Tax (Earnings and Pensions) Act 2003 — employment income (relevant for PAYE)

• The Income Tax (Pay As You Earn) Regulations 2003 — PAYE framework

• The Income Tax (Digital Requirements) Regulations 2021 — MTD-IT framework

• The Capital Allowances Act 2001 — capital allowances rules (AIA, WDA)

• The Construction Industry Scheme Regulations 2005 — CIS framework

• The Social Security Contributions and Benefits Act 1992 — National Insurance rules

• HMRC Self-Assessment Manual — operational guidance

• HMRC Business Income Manual — expense allowability detail

• HMRC — Self-Assessment registration and filing — primary HMRC guidance

• HMRC — Expenses if you're self-employed — allowable expenses guide

• HMRC — Capital allowances — AIA and WDA

• HMRC — Construction Industry Scheme — CIS rules

• HMRC — Making Tax Digital for Income Tax — MTD-IT guidance

• self-employment tax overview including NI and income tax bands — for tax fundamentals

• accounting software comparison for sole trader returns — for the tooling decision

• MTD overview including IT and VAT — for the regulatory framework

• CIS deduction handling and reclaim — for CIS detail

• sole trader vs limited company tax comparison — for the structural decision