To complete a Self Assessment tax return you need your Unique Taxpayer Reference, proof of every source of income for the tax year, and records of anything that reduces your bill, such as business expenses, pension contributions and Gift Aid. Gathering these before you sit down to file is what turns a stressful January evening into a straightforward job. Use the checklist below for your 2025/26 return, which is due online by 31 January 2027.
Key takeaways
- The 2025/26 tax year ran from 6 April 2025 to 5 April 2026. Every document should relate to that period.
- The paper return deadline is 31 October 2026 and the online deadline is 31 January 2027.
- You report figures to HMRC, not paperwork, but you must keep the evidence.
- Do not forget small items: bank interest, dividends, a second job, or a few months of rental income all count.
- Missing the online deadline brings an automatic £100 penalty, even if no tax is due.
What is a Self Assessment return?
Self Assessment is the system HMRC uses to collect Income Tax from people whose tax is not fully dealt with through PAYE, such as the self-employed, landlords, company directors with dividend income and people with untaxed income. You report your income and claims for a tax year on a Self Assessment tax return, HMRC calculates what you owe, and you pay it by the deadline. If you have never filed before, you must register first. See our guide to the Self Assessment registration deadline, which is 5 October following the end of the tax year.
The dates that matter
- 5 April 2026: end of the 2025/26 tax year.
- 5 October 2026: deadline to register if you are new to Self Assessment.
- 31 October 2026: deadline for paper returns.
- 31 January 2027: deadline for online returns and for paying the tax due for 2025/26, plus any first payment on account for 2026/27.
- 31 July 2027: second payment on account, where they apply.
These are confirmed on the GOV.UK deadlines page. If paper is your preference, read our note on the paper tax return deadline.
The document checklist
Not every row will apply to you. Work down the list and tick off the ones that do.
| If you have | Gather | Where to find it |
|---|---|---|
| Any return to file | UTR, National Insurance number, Government Gateway login | HMRC letters, personal tax account, HMRC app |
| Self-employment | Total sales, expenses by category, mileage log, asset purchases | Bookkeeping software, bank statements, invoices and receipts |
| Employment | P60, or P45 if you left; P11D for benefits | Employer or payroll portal |
| Savings | Interest received on each account, 6 April to 5 April | Annual interest statements from banks and building societies |
| Shares or your own company | Dividend vouchers showing dates and amounts | Company records, broker or platform tax statements |
| Rental property | Rent received, agent statements, repairs, insurance, mortgage interest | Letting agent, bank statements, lender's annual statement |
| Pensions in payment | P60 from each pension provider, State Pension amount | Pension provider, DWP letter |
| Sold assets | Purchase and sale dates, costs and proceeds | Completion statements, broker reports |
| Pension contributions | Amounts paid personally in the year | Pension provider's annual statement |
| Charity donations | Gift Aid donations made | Charity receipts, bank statements |
| Student loan | Plan type and any repayments already deducted through PAYE | Payslips, P60, Student Loans Company account |
| Child Benefit | Amount received in the year, if the High Income Child Benefit Charge may apply | Child Benefit award letter, bank statements |
| Paid tax already | Payments on account made in January and July | HMRC online account, bank statements |
Extra records if you are self-employed
The self-employment pages need more than a single profit figure. Have ready:
- Total business income, including cash, tips and platform payouts before fees.
- Expenses grouped by type. Our guide to sole trader allowable expenses explains what usually counts.
- Business mileage, if you claim simplified mileage instead of actual vehicle costs.
- Details of equipment or vehicles bought or sold in the year.
- Any use of home figures. See working from home expenses.
- Losses carried forward from earlier years.
HMRC sets out what the self-employed must keep in its guidance on business records if you're self-employed.
Step by step: getting ready to file
- Check you can log in. Test your Government Gateway details now. Recovering access in late January is slow.
- List your income sources. Write down every place money came from between 6 April 2025 and 5 April 2026.
- Collect one document per source. Use the table above and save everything into a single folder.
- Total your business figures. Reconcile them to your bank statements so that nothing is missing.
- Collect your reliefs. Pension contributions, Gift Aid and similar.
- Check what you have already paid. Payments on account reduce the balance due.
- Complete or hand over the return. Then review the calculation before it is submitted.
- Plan the payment. Know the amount and the date. See Self Assessment payment methods and deadlines.
Worked example (illustrative)
"Priya", an illustrative example, works three days a week as an employed designer and freelances on the other two. She also has a savings account and gives monthly to a charity under Gift Aid.
In October 2026 she makes a folder and collects: her P60 from her employer; a spreadsheet of freelance invoices totalling £14,200 and expenses of £2,150 with receipts; an annual interest statement showing £310; a pension statement showing £1,200 of personal contributions; and her Gift Aid receipts for £240. She confirms in her HMRC account that she made no payments on account. With everything in one place, the return takes under an hour to complete in November, and she has more than two months to set aside the tax before 31 January 2027.
The figures are invented purely to show what a complete pack looks like.
Common mistakes
- Using the wrong year's documents. A P60 dated 5 April 2026 is the right one for the 2025/26 return.
- Leaving out savings interest or dividends. HMRC receives information from banks and other institutions, so omissions are often noticed.
- Entering net figures from platforms. Report gross income and claim fees as an expense.
- Forgetting payments on account. This leads to a nasty surprise or an overpayment.
- Starting in the last week of January. Replacement documents and login resets take time. Our guide to late filing penalties shows what a missed deadline costs.
How we can help
Send us the documents on this checklist and we will prepare and file your return, explain the calculation and tell you exactly what to pay and when. Personal tax returns start from £180 per year on a fixed fee. See our Personal Tax service, view our pricing, or contact us to get started well before January.
Frequently Asked Questions
What documents do I need for a Self Assessment tax return?
You need your Unique Taxpayer Reference and National Insurance number, plus evidence of every type of income: self-employment records, P60 or P45 and any P11D from employment, bank interest statements, dividend vouchers, rental records and pension statements. You also need records of reliefs such as pension contributions and Gift Aid, and details of payments on account already made.
Do I send the documents to HMRC with my return?
No. An online Self Assessment return asks for figures, not attachments, in almost all cases. You keep the documents yourself as evidence in case HMRC asks to see them later. If you are self-employed, you must keep records for at least 5 years after the 31 January submission deadline for that tax year.
What if I cannot find my P60?
Ask your employer for a replacement. They can issue a copy. You can also see your pay and tax for the year in your HMRC personal tax account or the HMRC app, and your final payslip of the tax year will normally show the year to date totals for pay and tax deducted.
Where do I find my UTR number?
Your Unique Taxpayer Reference is a 10-digit number. It appears on previous tax returns, on letters from HMRC about Self Assessment such as a notice to file or a statement of account, and in your HMRC personal tax account or the HMRC app. If you have never registered, you will need to do that first.
When should I start gathering documents?
As soon as the tax year ends on 5 April. Most documents are available by early summer, since employers must provide P60s by 31 May and P11Ds by 6 July. Collecting everything then means you can file months before the 31 January online deadline and know your bill well in advance.
Related reading
How Berber Accounts & Tax helps
We are a London-based, specialist gig-economy and MTD accounting practice working with fixed monthly fees. If you would like this handled for you rather than doing it yourself, we can help.
Schedule a consultation →Written by the Berber Accounts & Tax team, 124 City Road, London EC1V 2NX, United Kingdom.
Last reviewed: 4 October 2026.
This article is general information, not personal tax advice. Speak to a qualified accountant about your own circumstances before acting on it.