Self Assessment Tax Return Guide 2026/27
Self Assessment is the system HMRC uses to collect Income Tax from people who don't have it deducted automatically. This guide covers everything you need to know for the 2026/27 tax year.
Who Needs to File a Self Assessment?
You must file a Self Assessment tax return if you:
- Are self-employed and earned over £1,000
- Are a partner in a business partnership
- Had income over £150,000
- Received rental income
- Had savings or investment income over £10,000
- Received foreign income
- Need to pay Capital Gains Tax
- Need to pay the High Income Child Benefit Charge
- Are a company director (unless no tax to pay)
- Received tips or commission
- Had income from trusts
Key Deadlines for 2026/27 Tax Year
| Action | Deadline |
|---|---|
| Tax year ends | 5 April 2027 |
| Register for Self Assessment | 5 October 2027 |
| Paper tax return deadline | 31 October 2027 |
| Online tax return deadline | 31 January 2028 |
| Pay tax owed | 31 January 2028 |
| Second payment on account | 31 July 2028 |
Payments on Account
If you owe more than £1,000 in Self Assessment, you'll need to make payments on account:
- First payment: 31 January (during the tax year)
- Second payment: 31 July (after the tax year)
Each payment is 50% of the previous year's tax bill.
What Income to Declare
Employment Income:
- Salary, wages, bonuses
- Benefits in kind
- Redundancy pay over £30,000
- Tips and gratuities
Self-Employment Income:
- Business profits
- Freelance earnings
- Side hustle income
Property Income:
- Rental income
- Holiday let profits
- Property sale gains
Investment Income:
- Dividends over £500
- Savings interest over £1,000/£500
- Capital gains over £3,000
Other Income:
- Pension income
- Foreign income
- Trust income
Allowable Expenses for Self-Employed
Reduce your taxable profit by claiming:
- Office costs and equipment
- Travel expenses (not commuting)
- Staff costs
- Stock and materials
- Marketing and advertising
- Professional fees
- Training courses
- Proportion of home costs (if working from home)
Penalties for Late Filing
| Delay | Penalty |
|---|---|
| 1 day late | £100 fixed penalty |
| 3 months late | £10 per day (up to 90 days) |
| 6 months late | 5% of tax due or £300 (whichever is higher) |
| 12 months late | Additional 5% or £300 |
Late Payment Penalties:
- 30 days late: 5% of tax unpaid
- 6 months late: Additional 5%
- 12 months late: Additional 5%
Plus interest on outstanding amounts.
How to File Your Tax Return
Option 1: HMRC Online
- Free to use
- Automatic calculations
- 24/7 access
- Deadline: 31 January
Option 2: Commercial Software
- More features than HMRC's service
- Often integrates with accounting software
- May have a cost
Option 3: Paper Return
- Earlier deadline (31 October)
- Manual calculations required
- Not recommended
Tips for a Smooth Filing Process
- Gather documents early - P60s, P45s, bank statements, receipts
- Keep records organised - Digital storage recommended
- Don't wait until deadline - File early to avoid stress
- Double-check figures - Errors can trigger enquiries
- Pay what you can - Even partial payment reduces interest
Calculate Your Tax Bill
Use our Self Assessment Calculator to estimate your Income Tax and National Insurance before filing.
Related Topics
Waqas Sagar
ACA, FCCA, FMAAT - Chartered Accountant
Waqas is a Chartered Accountant regulated by ICAEW, ACCA and AAT with 18+ years of UK tax experience. He is the founder of Accotax, a London-based accountancy firm serving over 1,200 clients.
Accuracy Note
This information is for guidance only and is based on 2026/27 tax year rates. Tax rules are complex and your circumstances may differ. For personal advice, consult a qualified accountant or tax adviser.