How to Fill in Your Self Assessment Tax Return Online

Filling in your Self Assessment return online is more straightforward than most people expect. Here is a section-by-section walkthrough.

Logging In

Go to GOV.UK and search for "file your Self Assessment tax return." Log in with your Government Gateway user ID and password. Select the tax year you are filing for.

Section 1: Personal Details

Confirm your name, address, National Insurance number, and UTR. Update anything that has changed.

Section 2: Tailor Your Return

HMRC asks what types of income you have. Tick the boxes that apply:

• Self-employment
• Property income
• Employment income (if not fully covered by PAYE)
• Foreign income
• Capital gains
• Other income

This determines which supplementary pages appear.

Section 3: Self-Employment Pages

This is the main section for sole traders:

Income: Enter your total business turnover (total sales before expenses).

Expenses: Enter your expenses by category. HMRC provides standard categories:

• Cost of goods
• Car, van, and travel
• Wages, salaries, and other staff costs
• Rent, rates, power, and insurance
• Repairs and renewals
• Phone, fax, stationery, and other office costs
• Advertising and business entertainment
• Interest and bank charges
• Professional fees
• Depreciation and loss on sale
• Other expenses

Net profit: HMRC calculates this automatically from your income minus expenses.

Capital allowances: Enter any claims for business equipment, vehicles, or other assets.

Section 4: Other Income

Enter any employment income (from your P60), savings interest, dividends, or other taxable income.

Section 5: Tax Reliefs

Enter pension contributions, Gift Aid donations, and any other reliefs you are claiming.

Section 6: Review and Submit

HMRC generates a tax calculation showing:

• Your total income
• Allowable deductions
• Taxable income
• Income Tax due
• National Insurance due
• Total tax liability
• Tax already paid (through PAYE, payments on account)
• Amount due or refund

Review this carefully. If it looks right, submit the return.

Tips for Accuracy

• Have all your figures ready before you start
• Use software like Accounted to prepare your figures throughout the year
• Double-check your turnover against your bank statements
• Ensure expenses are in the right categories
• Save regularly as you go — HMRC's system allows you to save and return later

Stop dreading your Self Assessment. Accounted tracks everything throughout the year so January is just a click, not a crisis. Try it free.