Guide

File your Self Assessment tax return

Step-by-step guidance for sole traders on completing and submitting your Self Assessment tax return to HMRC, including key deadlines, payment schedules, and how to avoid penalties.

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As a sole trader, you must submit a Self Assessment tax return each year to report your business income and expenses to HMRC. This guide covers everything you need to know about filing your return, from key deadlines to avoiding costly penalties.

Who needs to file Self Assessment?

You must file a Self Assessment return if your self-employment income exceeds £1,000 in the tax year (known as the trading allowance). Even if you have no tax to pay, you must still file if HMRC has asked you to or if you're registered for Self Assessment.

First time filing? Make sure you've registered for Self Assessment by 5 October following the end of the tax year in which you started trading. You'll receive a Unique Taxpayer Reference (UTR) which you'll need to file your return.

Key filing deadlines

Missing these deadlines will result in automatic penalties, even if you owe no tax:

Important: The 31 January deadline is both your filing deadline and your payment deadline. Plan ahead to avoid a last-minute rush when HMRC's systems are busiest.

Tip: File early in the tax year (from 6 April onwards) to get a clear picture of what you owe and spread your payments if needed. Filing early does not mean paying early - tax is still due by 31 January.

Payment deadlines

Understanding when to pay is just as important as knowing when to file. Your payment schedule depends on how much tax you owe:

Understanding payments on account

If your tax bill is substantial, HMRC requires advance payments towards next year's bill. These are called "payments on account" and can catch new sole traders by surprise.

Example: Your 2024/25 tax bill is £4,000. On 31 January 2026, you pay:

  • £4,000 - the tax you owe for 2024/25
  • £2,000 - first payment on account for 2025/26 (50% of previous year)

On 31 July 2026, you pay a further £2,000 (second payment on account). This means your first year with a substantial tax bill can feel like a double payment.

Reducing payments on account: If you expect your income to be significantly lower next year, you can apply to reduce your payments on account. Be cautious - if you reduce too much and underestimate, you'll pay interest on the shortfall.

Penalties for late filing

HMRC's penalty regime escalates quickly. Even one day late triggers an automatic penalty:

Key point: The £100 penalty applies even if you owe no tax. Many sole traders mistakenly think that because they have no tax liability, they don't need to file on time. This is wrong - the deadline applies to everyone.

Penalties for late payment

If you file on time but don't pay on time, a separate set of penalties applies:

Cannot pay in full? Contact HMRC before the deadline to arrange a Time to Pay plan. HMRC is often flexible with those who communicate proactively. Ignoring the bill leads to escalating penalties and potential debt recovery action.

What you'll need to complete your return

Gather these records before starting:

  • Income records: Invoices issued, bank statements showing income, till records
  • Expense records: Receipts, supplier invoices, mileage logs
  • P60/P45: If you also had employment income
  • Bank interest statements: Interest earned on savings accounts
  • Dividend vouchers: If you received any dividends
  • Pension contributions: Records of payments to private pensions
  • Previous year's return: Useful for reference and consistency

  1. Register for Self Assessment (if not already done)

    You need a UTR before you can file. Register by 5 October following the tax year you started trading. HMRC posts your UTR within 10 working days.

  2. Gather your records

    Collect all income and expense records for the tax year (6 April to 5 April). Include bank statements, invoices, and receipts.

  3. Calculate your profit

    Total income minus allowable expenses equals your taxable profit. Consider using accounting software or a spreadsheet to track this throughout the year.

  4. Log in to HMRC's Self Assessment service

    Use your Government Gateway account. Complete the SA100 main return and SA103S (short) or SA103F (full) supplementary pages for self-employment.

  5. Check the calculation

    HMRC's online service calculates your tax. Review this carefully before submitting. Save or print a copy for your records.

  6. Submit your return

    File online by 31 January. You'll receive an acknowledgement with a reference number - keep this safe.

  7. Pay any tax owed

    Pay by 31 January via bank transfer, Direct Debit, or debit card. Use your UTR as the payment reference.

Record keeping

You must keep your business records for at least 5 years after the 31 January submission deadline. For your 2024/25 return (deadline 31 January 2026), keep records until at least 31 January 2031.

Records to keep include:

  • Sales invoices and income records
  • Expense receipts and supplier invoices
  • Bank and building society statements
  • Mileage logs if claiming vehicle expenses
  • Records of assets bought or sold

Digital records: Photographs or scans of receipts are acceptable. Consider accounting software (FreeAgent, QuickBooks, Xero) to make record-keeping easier and prepare for Making Tax Digital.

Common mistakes to avoid

  • Missing the deadline: Set a reminder for mid-January at the latest
  • Forgetting payments on account: Budget for 150% of your tax bill in your first year if you expect ongoing profits
  • Claiming personal expenses: Only claim expenses that are wholly and exclusively for business
  • Not keeping receipts: HMRC can ask to see evidence for any expense claimed
  • Ignoring the trading allowance: If your turnover is under £1,000, you may not need to register or file at all
  • Using last year's thresholds: Tax rates and thresholds change annually - always check current figures

File your Self Assessment tax return

SOLE TRADER Requirement

File SA103 supplementary pages for self-employment

As a sole trader, you file:

  • SA100: The main Self Assessment tax return
  • SA103S (Short): For straightforward self-employment with turnover under £85,000
  • SA103F (Full): For more complex situations or turnover of £85,000 or more

The online Self Assessment service guides you through which pages you need based on your circumstances.

Comparison to other structures:

Company directors file employment income on SA102, with company profits reported separately through Corporation Tax returns.

When this matters: Choosing the correct form ensures HMRC receives accurate information about your business income and expenses.
Self Assessment forms (GOV.UK)

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