Filing your Self Assessment tax return does not have to be stressful. With the right documents and a clear plan, you can complete it in under an hour. This checklist covers everything you need for the 2026/27 tax year — from documents and deadlines to the exact steps for filing online.
This is the online filing deadline for the 2025/26 tax year. Miss it and you face an automatic £100 penalty — even if you owe no tax. The payment deadline is the same day.
Key Dates for 2026/27
| Date | What happens |
|---|---|
| 5 April 2026 | 2025/26 tax year ends |
| 5 October 2026 | Deadline to register for Self Assessment (newly self-employed) |
| 31 October 2026 | Paper tax return deadline |
| 31 January 2027 | Online filing deadline + payment + first payment on account |
| 31 July 2027 | Second payment on account |
Documents You Need to Gather
📋 Employment Income
- P60 from your employer (shows total pay and tax deducted)
- P45 if you left a job during the tax year
- P11D if you have taxable benefits (company car, medical insurance)
💰 Self-Employment Income
- All invoices issued to clients
- Bank statements showing business income
- CIS statements (if construction subcontractor)
- Cash income records
📈 Investment & Other Income
- Bank statements showing interest earned
- Dividend vouchers from shares
- Rental income and expense records
- Pension income statements
- Partnership income (SA800 form)
💲 Tax Reliefs & Deductions
- Pension contribution statements
- Gift Aid donation records
- Student loan statements (Plan 1, 2, 4 or postgraduate)
- Marriage Allowance details if applicable
- Child Benefit information (if income over £50,000)
Expense Records to Keep
If you are self-employed, you can deduct allowable business expenses from your taxable income. Make sure you have records for:
- Office costs (stationery, phone, broadband)
- Travel (mileage logs, train tickets, parking)
- Clothing (uniforms, protective equipment only)
- Staff costs (salaries, subcontractors)
- Financial costs (accountancy, insurance, bank charges)
- Marketing (website, advertising)
- Training (courses related to your business)
Claim £6/week (£312/year) flat rate without receipts. Or claim actual costs: calculate the business proportion of your home costs (heating, electricity, council tax, mortgage interest, rent, internet). You need to base this on the number of rooms used for business and hours worked.
Step-by-Step Filing Guide
Go to gov.uk/log-in-file-self-assessment-tax-return. Use your Government Gateway ID and password. If you have not registered, do so by 5 October 2026.
Verify your name, address, National Insurance number and UTR are correct. Update anything that has changed.
Fill in each income section: employment (from P60/P45), self-employment, property income, dividends, interest, pensions and foreign income. Enter the gross amounts and any tax already deducted.
For self-employment, enter your turnover and allowable expenses. HMRC will calculate your taxable profit. For property, enter rental income and allowable costs.
Enter pension contributions, Gift Aid donations, student loan repayments and any other reliefs. Higher Rate taxpayers: make sure you claim extra pension relief.
Review the calculation summary. Check the tax owed matches your expectations. Submit the return. You will receive a confirmation reference number. Save this.
Pay by 31 January 2027. Methods: Direct Debit, bank transfer, debit card. If your bill exceeds £1,000, your January payment includes the tax owed plus your first payment on account (50% of this year's bill).
How Much Will You Owe?
Use our calculators to estimate your tax bill before filing:
📊 Calculate Your Tax Before Filing
Use the right calculator for your situation to avoid surprises.
Sole Trader Calculator →5 Tips to File Without Stress
- Start in April, not January — File soon after the tax year ends. You will know what you owe and can budget.
- Use the HMRC app — Track your tax position throughout the year.
- Save as you go — Put 20-30% of every payment into a savings account for tax.
- Get an accountant if needed — For complex situations (CIS, foreign income, capital gains), professional help saves money and stress.
- File even if you cannot pay — The filing penalty (£100) is separate from the payment penalty. File on time to avoid both.
📝 Ready to File?
Head to HMRC's online portal and use this checklist to complete your return.
File on HMRC →