Requirements for Self Assessment tax return in the United Kingdom in 2026

If you are self-employed, a company director, a landlord, or you earn income that is not taxed at source, you are likely required to file a Self Assessment tax return with HMRC each year. The process tells HMRC how much income you received during the tax year (6 April to 5 April), calculates the tax you owe, and allows you to claim any allowable expenses or reliefs.

Filing on time and with accurate information is essential — late or incorrect returns can result in automatic penalties. The good news is that the process follows clear, predictable steps, and this guide sets out exactly what you need to have ready before you begin.

What this procedure is and what it’s for

Self Assessment is the system HMRC uses to collect Income Tax and National Insurance from people whose tax is not automatically deducted through PAYE (Pay As You Earn). Instead of your employer handling your tax, you report your own income and calculate what you owe.

You must register for and file a Self Assessment tax return if, in the relevant tax year, you:

• Were self-employed as a sole trader and earned more than £1,000 (before expenses)
• Were a partner in a business partnership
• Were a company director (unless your only income was a salary taxed through PAYE)
• Received rental income from property
• Had untaxed income from savings, investments or dividends above your allowances
• Earned more than £100,000 in total income
• Received Child Benefit and you or your partner earned more than £60,000 (High Income Child Benefit Charge)
• Were employed but had additional untaxed income above £2,500
• Were a trustee or personal representative of an estate

The official body responsible for Self Assessment in the United Kingdom is HMRC (His Majesty’s Revenue and Customs). The return is filed online via the HMRC online services portal using a Government Gateway account, or by post using a paper SA100 form (paper filing has an earlier deadline).

Documents required

Before you start your return, gather the following. You do not submit most of these as attachments — you use them to fill in the figures accurately. Keep originals for your own records for at least five years after the filing deadline.

Proof of identity and registration

• Your Unique Taxpayer Reference (UTR) — a 10-digit number issued by HMRC when you register for Self Assessment. Find it on previous HMRC correspondence or in your Government Gateway account.
• Your National Insurance (NI) number — found on your NI card, a payslip, a P60, or a letter from HMRC or the Department for Work and Pensions.
• Your Government Gateway user ID and password — created when you first registered online with HMRC.

Income records

• P60 (if employed) — your end-of-year certificate showing total pay and tax deducted by your employer.
• P45 — if you left a job during the tax year.
• P11D or P11D(b) — if you received taxable benefits in kind from an employer (e.g. a company car).
• Self-employment income records — invoices, sales records, or a profit and loss summary showing your total turnover and allowable expenses.
• Rental income records — rent received, mortgage interest statements, letting agent statements, and receipts for allowable expenses.
• Bank and savings statements — showing interest earned (your bank may provide an annual summary).
• Dividend vouchers or statements — from shares or investment funds.
• Pension income statements — from private or workplace pension providers.
• State Pension letter — from the Department for Work and Pensions confirming your annual State Pension amount.
• Foreign income records — if you received income from abroad, including exchange rate information.

Expenses and reliefs

• Receipts and invoices for allowable business expenses — for example, office costs, travel, equipment, professional subscriptions.
• Gift Aid donation records — amounts donated to charity under Gift Aid during the year.
• Pension contribution records — personal pension contributions paid outside of PAYE, to claim tax relief.
• Student Loan repayment details — if you are repaying a student loan, HMRC will calculate the amount due; have your loan plan type to hand (Plan 1, Plan 2, Plan 4 or Postgraduate Loan).
• Capital Gains records — if you sold assets (property, shares, cryptocurrency) during the year: purchase price, sale price, dates and any associated costs.

Notes on originals and copies

No documents need to be certified, apostilled or translated for a standard UK Self Assessment return. You retain originals yourself. If HMRC opens an enquiry into your return, they may request supporting evidence at that stage.

Steps to complete the procedure

Step 1 — Register for Self Assessment (if you have not done so before)

If this is your first time filing, you must register with HMRC before you can submit a return. Do this as early as possible — registration can take up to 10 working days to process.

• Self-employed individuals: register at gov.uk/register-for-self-assessment
• Other reasons (e.g. rental income, director): use the SA1 form, available on the same page.
• Once registered, HMRC will send your UTR by post.

Step 2 — Set up or access your Government Gateway account

Go to www.gov.uk/log-in-file-self-assessment-tax-return and sign in with your Government Gateway user ID. If you do not have one, create an account — you will need your UTR and NI number to hand.

Step 3 — Gather all your income and expense figures

Using the documents listed above, calculate your total income from each source and your total allowable expenses. If you use the cash basis of accounting (common for sole traders with turnover under £150,000), record income when received and expenses when paid.

Step 4 — Complete the online return

Log in to the HMRC Self Assessment portal. The system guides you through each section:

• Personal details and NI number
• Employment income (from P60 / P45)
• Self-employment income and expenses (or use the SA103 supplementary pages)
• Property income (SA105 supplementary pages)
• Capital gains (SA108 supplementary pages)
• Foreign income (SA106 supplementary pages)
• Reliefs and allowances (Gift Aid, pension contributions, etc.)

The online system calculates your tax liability automatically as you enter figures.

Step 5 — Review and submit

Check all figures carefully before submitting. Once submitted, you will receive an online confirmation and a submission reference number. Save or print this for your records.

Step 6 — Pay any tax owed

After submitting, your tax bill is shown in your HMRC online account. Pay by the 31 January deadline to avoid interest and surcharges. Payment methods include online banking, debit card via the HMRC portal, or bank transfer using HMRC’s bank details.

No appointment needed

The entire process is done online. No office visit or prior appointment is required for a standard return. If you prefer to file by paper (SA100 form), download it from gov.uk/self-assessment-tax-return-forms and post it to HMRC.

Estimated time

• Gathering documents: 1–3 hours depending on complexity.
• Completing the online return: 1–4 hours for a straightforward return; longer if you have multiple income sources or capital gains.
• HMRC processes online returns and updates your account within a few days of submission.

Fees and timelines

• Filing fee: There is no fee to file a Self Assessment tax return. HMRC does not charge for submitting your return.
• Tax payment: You pay the Income Tax and National Insurance calculated by your return. The amount depends entirely on your income and circumstances.
• Payments on account: If your tax bill is more than £1,000, HMRC may require advance payments (payments on account) towards the following year’s tax — due 31 January and 31 July.
• Registration deadline: Register for Self Assessment by 5 October following the end of the tax year in which you became liable (e.g. by 5 October 2026 for the 2025–26 tax year).
• Paper return deadline: 31 October following the end of the tax year (e.g. 31 October 2026 for the 2025–26 tax year).
• Online return deadline: 31 January following the end of the tax year (e.g. 31 January 2027 for the 2025–26 tax year).
• Payment deadline: 31 January — the same date as the online filing deadline. Tax owed must be paid by this date to avoid interest charges.
• Late filing penalty: An automatic £100 penalty applies if you miss the 31 January deadline, even if no tax is owed. Further daily penalties of £10 (up to £900) apply after 3 months.
• Late payment interest: HMRC charges interest on unpaid tax from 1 February.
• How long to keep records: You must keep supporting records for at least 5 years after the 31 January filing deadline for that tax year (self-employed) or at least 22 months after the end of the tax year (employees and landlords).

Common mistakes and how to avoid them

• Missing the registration deadline: If you are newly self-employed or have a new source of untaxed income, you must register by 5 October. Many people miss this and face penalties. Set a calendar reminder as soon as your circumstances change.
• Entering income figures incorrectly from a P60 or P11D: Always cross-check figures directly from the official document rather than estimating from payslips. Errors here can trigger an HMRC enquiry or result in underpayment.
• Forgetting to include all income sources: Rental income, savings interest, dividends, foreign income and capital gains must all be declared. Omitting any source — even if you believe it is below a threshold — can lead to penalties if HMRC identifies the discrepancy.
• Claiming non-allowable expenses: Not all business costs are deductible. For example, client entertainment, fines and personal expenses cannot be claimed. Only claim expenses that are wholly and exclusively for business purposes. HMRC’s guidance at gov.uk/expenses-if-youre-self-employed lists what qualifies.
• Paying late or to the wrong account: Always use HMRC’s official bank details and include your UTR as the payment reference. Payments sent without the correct reference can be misallocated, leaving your account showing an unpaid balance and triggering interest charges.

Frequently asked questions

Do I need to file a Self Assessment return if I am employed and pay tax through PAYE? Usually not — if your only income is a salary taxed through PAYE and you have no other untaxed income, you do not need to file. However, you must file if you also have self-employment income, rental income, or if your total income exceeds £100,000, among other triggers. Check the full list at gov.uk/check-if-you-need-a-tax-return.

What if I cannot pay my tax bill by 31 January? Contact HMRC before the deadline. If you owe less than £30,000, you may be able to set up a Time to Pay arrangement online, spreading payments over up to 12 months. Interest still applies, but this avoids the surcharge for non-payment. Do not simply ignore the bill — penalties escalate quickly.

Can I amend my return after I have submitted it? Yes. You can amend an online Self Assessment return up to 12 months after the 31 January filing deadline for that tax year. Log in to your HMRC online account, find the relevant return and select the option to make a correction. After 12 months, you must write to HMRC to request an amendment.

What is the difference between the cash basis and traditional accounting? The cash basis means you record income when you actually receive it and expenses when you actually pay them. Traditional (accruals) accounting records income and expenses when they are earned or incurred, regardless of when money changes hands. Most sole traders with turnover under £150,000 can use the cash basis, which is simpler. You choose your method when completing the self-employment pages of your return.

I lost my UTR number. How do I find it? Your UTR appears on any letter HMRC has sent you about Self Assessment, on your SA302 tax calculation, or in your Government Gateway account under ‘Self Assessment’. If you cannot find it, call the HMRC Self Assessment helpline on 0300 200 3310 (Monday to Friday, 8am to 6pm). Have your NI number ready to verify your identity.

What to do next

The single most important step is to confirm whether you need to file and, if so, to register with HMRC by 5 October following the relevant tax year. Once registered, gather your income records, log in to your Government Gateway account, and complete your return well before the 31 January online deadline.

The key documents to have ready are your UTR, your NI number, your P60 or self-employment income records, and any expense receipts you intend to claim.

Important notice: Tax rules and thresholds can change. Always verify the current requirements, deadlines and allowances directly with HMRC at www.gov.uk/self-assessment-tax-returns or by calling the HMRC Self Assessment helpline on 0300 200 3310 before you begin your return.