Self Assessment for sole traders

How sole trader tax works

A sole trader is self-employed and runs a business in their own name. Legally, there is no separation between the person and the business — all profits belong to the individual, and all business debts are personal responsibilities.

Unlike a limited company, a sole trader does not file Corporation Tax returns or company accounts with Companies House. Instead, business income and expenses feed into the annual Self Assessment return alongside any other personal income, such as employment wages or rental profits.

HMRC taxes sole traders on profits, not turnover. Profit is what remains after allowable business expenses are deducted from total income. National Insurance on self-employed profits is calculated separately but appears on the same Self Assessment bill.

Understanding this structure helps sole traders keep the right records throughout the year rather than scrambling at filing time.

Registering as a sole trader

Before trading starts, sole traders must register for Self Assessment with HMRC. Registration is done online and should happen by 5 October after the tax year in which trading began.

After registration, HMRC sends a Unique Taxpayer Reference (UTR) by post. The UTR is needed to file the return. The full registration and filing process is covered in the how to file Self Assessment guide.

Sole traders whose turnover exceeds the VAT registration threshold must also register for VAT. That is a separate obligation from Self Assessment, though VAT figures may affect record-keeping.

Records HMRC expects

Good records make filing faster and support the figures if HMRC asks questions later. HMRC requires business records to be kept for at least five years after the 31 January filing deadline for the relevant tax year.

Useful records include:

• Sales records — invoices, till rolls, or platform statements showing money received
• Purchase records — receipts for stock, materials, and services bought for the business
• Bank statements — ideally a dedicated business account, though a separate record of business transactions works too
• Mileage logs — date, destination, purpose, and miles driven for business trips
• Contracts and agreements — with clients, suppliers, or landlords
• Cash book — if cash payments are common, a simple log of money in and out

Digital copies are acceptable if they are clear and easy to find. Photos of receipts stored in dated folders are widely used by sole traders.

HMRC can charge penalties for poor record-keeping, even when the tax figures themselves are correct. Organised records reduce that risk.

Working out business profit

The basic calculation is straightforward:

Turnover (all money earned from the business) minus allowable expenses equals taxable profit.

Turnover includes all business income, whether invoiced formally or received through payment platforms. Income must be declared for the tax year it was earned, not when it was paid — known as the accruals basis. Cash basis accounting is available for smaller businesses and records income when received.

Sole traders who qualify may instead use the £1,000 trading allowance. This lets them count £1,000 of trading income as tax-free without claiming expenses. It suits side hustles and very small ventures where expenses are low. Once profits exceed £1,000, the full Self Assessment rules apply.

Allowable expenses

Expenses reduce taxable profit only when they are wholly and exclusively for business purposes. Personal costs cannot be claimed, and mixed-use items need careful splitting.

Common allowable expenses for sole traders include:

• Office costs — stationery, printing, postage, and phone bills used for business
• Premises costs — rent, business rates, utilities, and insurance for business premises
• Travel — vehicle running costs or the approved mileage rate, train fares, and accommodation on business trips (not ordinary commuting)
• Clothing — uniforms or protective gear, but not everyday clothing
• Staff costs — salaries, employer National Insurance, and subcontractor payments
• Stock and materials — goods bought to resell or materials used in providing services
• Financial costs — bank charges, insurance, and interest on business loans
• Marketing — website costs, advertising, and business cards
• Professional fees — accountant, solicitor, or surveyor fees for business work
• Training — courses that maintain or update existing business skills (not training for a new career)

Some costs need special rules. Using a home as an office, for example, can be claimed through simplified expenses (a flat rate based on hours worked at home) or by calculating the actual proportion of household costs. Vehicle costs can use simplified mileage rates instead of tracking fuel and repairs.

The allowable expenses guide walks through categories in more detail with worked examples.

Expenses that are not allowable include personal living costs, client entertainment (in most cases), fines, and depreciation handled through capital allowances instead.

Capital allowances

When a sole trader buys equipment, vehicles, or other assets for the business, the full cost is not usually claimed as a one-off expense. Instead, capital allowances spread the tax relief over time.

The Annual Investment Allowance (AIA) lets most businesses deduct the full cost of qualifying plant and machinery in the year of purchase, up to a set limit published by HMRC. Items that do not qualify for AIA may fall under writing down allowances at prescribed rates.

Cars have separate rules depending on emissions. Keeping purchase invoices and dates matters for capital allowance claims.

National Insurance for sole traders

Self-employed people pay two classes of National Insurance on their profits:

Class 2

Class 2 is a flat weekly amount. It counts towards State Pension entitlement and certain benefits. Taxpayers with profits below the Small Profits Threshold may not need to pay Class 2, though voluntary payments are sometimes worthwhile for pension credits.

Class 4

Class 4 is a percentage charge on profits above a lower threshold. It does not count towards benefit entitlements in the same way as Class 2. Rates and thresholds are set each tax year and published on GOV.UK.

Both Class 2 and Class 4 are calculated through Self Assessment and appear on the same tax bill as Income Tax. They are not collected through PAYE unless the sole trader also has employed income with a special coding adjustment.

Current rates and thresholds are on Self-employed National Insurance rates.

Which return sections to complete

The Self Assessment return (form SA100) is the main document. Sole traders with business income also complete supplementary pages:

SA103S — short self-employment pages

For simpler businesses with turnover under £85,000 (threshold set by HMRC and subject to change). Fewer boxes to complete.

SA103F — full self-employment pages

For larger turnovers, more complex affairs, or when the short pages do not apply.

The online filing system usually selects the right pages based on answers given at the start. Key boxes on the self-employment pages include:

• Business details — name, description, and accounting dates
• Turnover — total sales and other business income
• Expenses — either individual categories or a single total, depending on the method chosen
• Net profit or loss — carried forward to the main return
• Class 2 and Class 4 National Insurance — calculated from the profit figure

If the sole trader also has PAYE employment during the year, the employment pages (SA102) are needed too, using figures from the P60 form.

Other pages may apply for rental income (SA105), capital gains (SA108), or foreign income (SA106).

A full list of forms is on Self Assessment tax return forms.

Payments and cash flow

Sole traders pay Income Tax and National Insurance on profits through Self Assessment. Nothing is deducted automatically during the year unless the trader also works as an employee with PAYE.

That means setting aside money from each payment received is a practical habit. A common approach is to reserve a percentage of profit for tax, though the exact rate depends on total income and tax bands.

The main payment deadline is 31 January after the tax year ends. Sole traders who owed more than £1,000 in tax last year may also face payments on account in January and July. The payments on account guide explains how these advance payments are calculated.

Missing the 31 January deadline triggers late-filing penalties and interest on unpaid tax. The Self Assessment deadlines guide lists every date sole traders need on the calendar.

Simplified expenses and cash basis

HMRC offers simplified rules that reduce paperwork for smaller sole traders:

Cash basis accounting — record income when received and expenses when paid, rather than when invoiced. Available to businesses with turnover up to £150,000.

Simplified expenses — flat rates for working from home, living at business premises, and business mileage, instead of calculating actual costs.

These options suit many sole traders with straightforward affairs. Once turnover or complexity grows, traditional accounting may give more accurate results and better control.

Common sole trader mistakes

Mixing personal and business spending — without clear separation, expense claims become unreliable and HMRC may disallow them.

Claiming all home costs — only the business portion is allowable, or the simplified rate applies.

Forgetting payments on account — the January bill can be much larger than expected when advance payments are due on top of the balancing payment.

Missing the registration deadline — late registration does not stop the tax being owed; it can delay receiving a UTR and make on-time filing harder.

Not keeping evidence — estimates without receipts are risky if HMRC opens an enquiry.

Ignoring Class 2 National Insurance — even when profits are low, voluntary Class 2 payments may protect State Pension entitlement.

When a sole trader might incorporate

Some sole traders later form a limited company for commercial or tax reasons. That changes how tax is reported — company profits are taxed through Corporation Tax, and the director may need a separate personal Self Assessment return for dividends and salary.

The director Self Assessment guide covers personal filing obligations after incorporation.

Incorporation is a significant step with legal and accounting consequences beyond the scope of this guide.

Your next step

Sole traders preparing for their next return can review HMRC's official list of allowable expenses and check each cost against the wholly-and-exclusively rule: Expenses if you're self-employed.