How to Submit a Self Assessment Tax Return in the UK: A Complete Step-by-Step Guide

1. Register for Self Assessment

You must register with HMRC if you’re required to submit a Self Assessment tax return.

Who Needs to Register?

  • You are self-employed or a sole trader.
  • You earned income that hasn’t been taxed (e.g., freelance work, side jobs, or rental income).
  • You made over £100,000 in a year.
  • You need to report additional income such as dividends, savings, or capital gains.
  • You’re a partner in a business partnership.
  • You earned over £1,000 in self-employed income in the tax year.

How to Register:

  1. Go to the HMRC website: Register for Self Assessment.

  2. Choose the appropriate option:

    • Register as self-employed.
    • Register as a partner in a partnership.
    • Register as a taxpayer with untaxed income (e.g., rental income).

  3. HMRC will send you a Unique Taxpayer Reference (UTR) number.

    • This 10-digit number is essential for filing your return.
    • It can take up to 10 working days to arrive (or 21 days if you’re abroad).

  4. Once you have your UTR, create a Government Gateway account to access HMRC online services.

2. Gather Your Information

Before you start, gather all the records and documents you need.

Personal Details:

  • Your Unique Taxpayer Reference (UTR).
  • Your National Insurance (NI) Number.
  • Government Gateway ID and password.

Income Information:

  • Self-employed income details (e.g., total invoices issued or payments received).
  • Employment income (e.g., P60, P45, or payslips).
  • Rental income (from properties you let out).
  • Bank statements showing interest from savings accounts.
  • Dividend vouchers for income from shares.
  • Foreign income, if applicable.

Expenses and Deductions:

You’ll need records of any allowable expenses (costs that you can deduct from your income). These can include:

  • Self-Employed Business Costs:
    • Office expenses: stationery, printer ink, phone, or computer costs.
    • Travel expenses: mileage, fuel, train tickets, etc.
    • Staff wages: if you employ someone.
    • Business insurance.
    • Marketing costs (e.g., website fees, advertising).
  • Property Rental Costs:
    • Maintenance, repairs, letting agent fees, and mortgage interest.
  • Other Deductible Items:
    • Pension contributions.
    • Charitable donations (via Gift Aid).

Tax Already Paid:

  • Details of any tax deducted at source (e.g., from PAYE employment).
  • Payments on account made to HMRC in the previous year.

3. Log in to HMRC’s Online Service

Once you have everything ready, you’ll need to log in to your online account:

  1. Visit HMRC's Online Service.
  2. Use your Government Gateway ID and password to log in.
  3. Select "Self Assessment" and start the process.

4. Complete the Self Assessment Tax Return

The main form for filing your tax return is the SA100. You may need additional supplementary forms depending on your income types:

Main Form: SA100

This form covers:

  • Personal details (name, address, UTR, and NI Number).
  • Employment income (use your P60/P45 or payslips).
  • Income from pensions or state benefits.
  • Other income (interest, dividends, or foreign income).

Supplementary Forms:

  • SA103: For self-employed income.
  • SA105: For rental income from properties.
  • SA102: For employment income (if you had multiple jobs).
  • SA108: For capital gains (e.g., selling shares or property).
  • SA101: For other income, such as investments or trusts.

Step-by-Step Process for Completing Your Tax Return:

  1. Enter Personal Details: Confirm your information is correct.
  2. Declare Your Income:
    • Enter your total earnings from all sources (employment, self-employment, rentals, etc.).
  3. Report Expenses:
    • Input allowable expenses to reduce your taxable income.
  4. Adjustments and Deductions:
    • Include any payments like pension contributions, student loan repayments, or charitable donations.
  5. Review and Verify:
    • Check all figures and ensure they match your records. HMRC will prompt you if anything seems incorrect.
  6. Submit Your Return:
    • Once you’re satisfied, submit the return online.

5. Pay Your Tax Bill

After submitting your Self Assessment, HMRC will calculate the tax you owe. The amount is based on your:

  • Total income.
  • Deductions and allowable expenses.
  • Any tax already paid (like PAYE deductions).

Payment Deadlines:

  • 31 January: Deadline for:
    • Submitting your tax return for the previous tax year.
    • Paying any tax owed.
  • 31 July: Deadline for Payment on Account (advance payments towards next year’s tax).

How to Pay:

You can pay your tax bill using:

  • Online banking (bank transfer).
  • Debit or credit card.
  • Direct Debit (if you set it up in advance).
  • At your bank or building society.
  • Cheque sent by post.

6. Avoid Penalties

It’s essential to meet deadlines and ensure your information is accurate to avoid penalties.

Penalties for Late Filing:

  • Missed 31 January deadline: Automatic £100 fine.
  • 3 months late: £10 per day penalty (up to £900).
  • 6 months late: Additional £300 or 5% of the tax owed (whichever is higher).
  • 12 months late: A further £300 or 5% of the tax owed.

Penalties for Late Payment:

  • 5% of the tax due if unpaid after 30 days, 6 months, and 12 months.
  • HMRC also charges interest on overdue amounts.

7. Additional Tips

  • File Early: Don’t wait until the last minute. Filing early helps you avoid stress and spot any errors.
  • Keep Records: Maintain records of income, receipts, and invoices for at least 6 years.
  • Use Accounting Software: Tools like QuickBooks, Xero, or FreeAgent can help simplify the process.
  • Seek Professional Help: If your finances are complex, consider hiring an accountant to assist you.

Important Links:

Back to blog