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.