Filing Your Self Assessment Tax Return

Before You Start

Gather everything you need before sitting down to file. Having your records ready makes the process much faster:^[2]

P60 — from your employer (if you’re employed), showing total pay and tax deducted
P45 — if you left a job during the year
P11D — details of benefits in kind (company car, private medical, etc.)
Bank and savings statements — showing interest earned
Dividend vouchers — from any shares you hold
Business income and expense records — if self-employed
Rental income and expense records — if you’re a landlord
Pension contribution statements
Gift Aid receipts
Your UTR and Government Gateway login details

Filing Online

Most people file online through HMRC’s Self Assessment service. Here’s how:^[1]

Go to gov.uk and sign in with Government Gateway
Select the tax year you’re filing for
Work through each section, entering your income and claiming any deductions
HMRC’s system automatically calculates your tax as you go
Review the summary, check the figures, and submit
You’ll get an immediate confirmation with your tax calculation

The Main SA100 Form

Every Self Assessment return starts with the SA100 form, which covers:^[3]

Personal details and residency status
Employment income (from your P60)
Savings and investment income
Pension income
Other income
Tax reliefs (pension contributions, Gift Aid, etc.)
Student loan repayments

Supplementary Pages

If you have specific types of income, you’ll need additional forms:^[3]

Form	Used For
SA103	Self-employment income
SA104	Partnership income
SA105	Property income
SA106	Foreign income
SA108	Capital gains
SA109	Residence and remittance basis

The online system guides you through which supplementary sections you need based on your answers.

Filing Deadlines

Method	Deadline
Paper return	31 October following the tax year
Online return	31 January following the tax year
Payment	31 January following the tax year

For the 2025/26 tax year (ending 5 April 2026), the online filing and payment deadline is 31 January 2027.^[5]

Don’t wait until January. HMRC opens online filing from the following 6 April, so you can file as early as April. Filing early doesn’t mean you have to pay early — payment is still due 31 January.

After Filing

Once you submit, HMRC immediately calculates your tax and shows you either the amount you owe or the refund you’re due. You can view and download your SA302 tax calculation from your online account.^[2]

Using Commercial Software

You can also file through HMRC-recognised commercial software instead of the HMRC online portal. This is often preferred by accountants and may be required under Making Tax Digital.^[1] GoFile is HMRC-recognised for MTD Income Tax filing.

Frequently Asked Questions

When is the Self Assessment tax return deadline?

The deadline for online filing is 31 January following the end of the tax year. Paper returns must be filed by 31 October. Your tax payment is also due by 31 January.

What documents do I need to file my tax return?

Gather your P60 (employment income), P11D (benefits in kind), bank statements (interest earned), dividend vouchers, business income and expense records, pension contribution statements, Gift Aid receipts, and your Government Gateway login details.

Can I file my tax return early?

Yes. HMRC opens online filing from 6 April after the tax year ends. Filing early does not mean you have to pay early — payment is still due by 31 January. Filing early gives you more time to budget for your bill.

What is the SA103 form used for?

The SA103 is the supplementary page for self-employment income. Other supplementary forms include SA105 for property income, SA106 for foreign income, and SA108 for capital gains.

Sources

File your Self Assessment tax return online — GOV.UK
Self Assessment tax returns — GOV.UK
Self Assessment forms and helpsheets — GOV.UK
Estimate your Income Tax for the current year — GOV.UK
Self Assessment tax returns: deadlines — GOV.UK

How to File Your Self Assessment Tax Return