Self Assessment is how you report income and gains that need an individual tax return. A PAYE job does not settle every other income source. Check whether a return is required, gather the records for the correct tax year and file and pay by the applicable deadlines.
Check whether you need a return
For 2025/26, a sole trader with gross income over £1,000 generally needs to file. Other triggers include partnership membership, relevant gains and certain untaxed income or charges. PAYE salary alone is not a universal filing trigger. Use HMRC’s return checker, and do not ignore a notice to file while you seek clarification.
Know which year you are reporting
The 2025/26 tax year ran from 6 April 2025 to 5 April 2026. The usual online filing and payment deadline is 31 January 2027; paper filing is normally due by 31 October 2026. A specific HMRC notice can set a different filing date. If you need to register or reactivate after 5 October, follow the instructions in that notice and keep the tax payment deadline separate.
Build the figures from evidence
Collect PAYE documents, trade or rental records, interest and dividend statements, pension and donation details, gains and any loan-repayment information. Different income sources belong in the same personal return where required. Bank transfers between your own accounts are not fresh earnings.
A return and a payment are different steps
Review the complete return before it is filed, then keep the submission confirmation. Check the tax calculation and HMRC account for what remains payable. PAYE or CIS already deducted can affect the balance; payments on account can add advance payments for the following year.
If MTD applies as well
MTD changes how in-scope business and property income is recorded and reported. It does not wipe out an earlier return. Keep 2025/26 Self Assessment and 2026/27 MTD work on separate timelines.
Use the document checklist to prepare. If you want accountant-led help, compare TaxSimba’s current packages and describe all income sources before buying.
Check the home nation used for your tax calculation
Tell the accountant whether you live in England, Scotland, Wales or Northern Ireland, and about any moves during the tax year. Scottish rates differ for wages, pensions and most other taxable income; savings and dividends use UK rules. Welsh rates are set separately. Use the rules for the relevant year and your actual taxpayer status.
See Scottish Income Tax and Welsh Income Tax. These differences do not make a London address or an England-only earnings example appropriate for everyone.
Follow one return from start to finish
Illustrative preparation example.
You discover that your side business may need reporting. First check the filing requirement, then confirm registration, gather the correct year’s figures, review the draft, obtain filing evidence and arrange any payment. Put these tasks on a timeline so registration is not mistaken for a finished return.
Check: What is the next unfinished step, and what evidence will show it is done?
| Check | Practical action |
|---|---|
| Need to report | Use the official checker and relevant HMRC notices. |
| Preparation | Gather income, allowable-cost and tax-deducted evidence. |
| Completion | Check both filing confirmation and payment obligations. |
Does opening a business account register me with HMRC?
No. Check the separate notification and registration steps that apply to your circumstances.
Does a nil tax bill always mean no return?
No. The filing requirement and the tax calculation are different questions; address any HMRC notice.
Download a checklist for this guide
- Tax year and HMRC notices
- Income sources and start dates
- Income and expense records
- Tax already deducted
- Registration, filing and payment next steps