Self Assessment Tax Return: Step-by-Step Guide for Freelancers

Who Needs to File a Self Assessment Return?

If you earned more than £1,000 from self-employment in a tax year, you must register for Self Assessment with HMRC and file a tax return. The tax year runs from 6 April to 5 April the following year.

You also need to file if you're a company director, have income from property, or earn over £100,000 as an employee. If in doubt, HMRC's online checker can confirm whether you need to register.

Step 1: Register with HMRC

If you haven't already, register as self-employed at gov.uk/register-for-self-assessment. You'll need your National Insurance number and contact details. HMRC will send your Unique Taxpayer Reference (UTR) number by post within about 10 working days — you need this to file.

Step 2: Gather Your Records

Before you sit down to file, pull together:

Total income from all clients (invoices raised and paid)
Allowable business expenses with receipts
Any other income (employment, rental, savings interest)
Bank statements to cross-reference figures
Details of any payments on account already made

Good record-keeping throughout the year makes this process much faster. If you use accounting software, most of this information is already categorised.

Step 3: Log In to Your HMRC Online Account

Go to gov.uk/log-in-file-self-assessment-tax-return and sign in with your Government Gateway credentials. If you don't have these, you'll need to set them up first — allow a week for activation codes to arrive.

The return has several sections. As a self-employed sole trader, you'll mainly complete the Self-employment (short) or Self-employment (full) pages.

Step 4: Fill in Your Income and Expenses

Enter your gross turnover (total invoiced amount before expenses), then your allowable expenses. HMRC calculates your profit automatically. Alternatively, use the trading allowance (£1,000) if your expenses are below this — though for most freelancers, actual expenses will be higher.

Common allowable expenses include: professional subscriptions, software, home office costs, travel, equipment, and marketing. Do not include personal expenses or fines.

Step 5: Check for Reliefs and Allowances

Before submitting, review whether you qualify for any additional reliefs:

Pension contributions: Personal pension payments reduce your taxable income
Gift Aid donations: Can extend your basic rate band
Marriage allowance: If your partner earns below the Personal Allowance
Capital allowances: For equipment purchased for business use

Step 6: Review Your Calculation

HMRC's system will show you the tax owed before you submit. Check this against your own calculation. If the figures look very different from what you expected, review your entries for errors before proceeding.

Key Deadlines

5 October: Register for Self Assessment if you're newly self-employed
31 October: Deadline for paper returns
31 January: Deadline for online returns and payment of tax owed
31 July: Second payment on account due

Penalties for Late Filing

Missing the 31 January deadline triggers an automatic £100 penalty, even if you owe no tax. Further penalties accrue daily after 3 months. Always file on time, even if you can't pay immediately — HMRC would rather arrange a payment plan than see you incur avoidable penalties.