Self Assessment Guide 2025/26
Over 12 million people in the UK need to file a Self Assessment tax return each year. Whether you’re self-employed, a landlord, a director, or earn over £100,000 — this guide walks you through exactly what to do, what information you need, and how to avoid penalties.
Key Deadlines — Never Miss These
31 Jan
🔴 Online return filing deadline + tax payment due
31 Oct
🟡 Paper return filing deadline
5 Oct
🟢 Deadline to register for Self Assessment
The most important deadline is 31 January — this is both the online filing deadline AND the payment deadline for any tax owed. You will also need to pay a Payment on Account (50% of your estimated next year’s tax bill) on the same date.
Don’t wait until January!
HMRC’s systems are under huge pressure in January. Filing early — ideally before December — reduces stress, gives you time to arrange funds to pay your tax bill, and reduces the risk of last-minute technical issues.
Who Needs to File a Self Assessment?
- Self-employed sole traders with income over £1,000
- Partners in a business partnership
- Company directors (including non-executive directors)
- People earning over £100,000 (income over the personal allowance taper)
- Landlords with property rental income over £2,500
- People with capital gains to declare
- Employees with additional untaxed income over £2,500
- Anyone who has received Child Benefit and earns over £60,000
- People with savings interest or dividend income above their allowances
Step 1 — Register for Self Assessment
1
Register Online with HMRC (if first time)
If you have never filed a Self Assessment return before, you must register with HMRC first. Go to gov.uk/register-for-self-assessment. You will need your National Insurance number and contact details.
After registering, HMRC will send you a Unique Taxpayer Reference (UTR) by post within 10 working days. This 10-digit number is essential — you cannot file without it. Register well before the 5 October deadline.
2
Set Up Your Government Gateway Account
To file online, you need a Government Gateway account. If you don’t have one, create it at gov.uk/log-in-register-hmrc-online-services. You’ll receive an activation code in the post (allow 7 days).
If you already have a Government Gateway account from a previous year, simply log in with your existing credentials.
Step 2 — Gather Your Information
Before you start your return, collect all the information you’ll need. This takes time — don’t leave it until the night before the deadline.
Self-Employment Income
Total turnover from your business for the tax year (6 April – 5 April)
Business Expenses
All allowable business expenses paid during the tax year (keep receipts)
P60 / P45 from Employment
If you also had employment income alongside self-employment
P11D Benefits in Kind
If your employer provided benefits like a company car or health insurance
Rental Income Details
Gross rental income and allowable letting expenses if you have property
Bank Interest Statements
Annual interest statements from all savings accounts
Dividend Vouchers
Dividend statements from investments and any limited company dividends
Capital Gains Records
Details of any assets sold during the year (shares, property, crypto)
Pension Contributions
Any personal pension contributions paid gross (for higher-rate relief claims)
Gift Aid Donations
Total charitable donations made under Gift Aid during the year
Step 3 — Complete Your Return
3
Log Into HMRC Online and Start Your Return
Go to gov.uk/file-your-self-assessment-tax-return and log in. Select “Complete your tax return” and ensure you are completing the return for the correct tax year.
HMRC’s online system will guide you through relevant sections based on your answers. You don’t need to complete every section — only those that apply to your circumstances.
4
Complete the Self-Employment Pages
Enter your total business income (turnover) and total allowable expenses. HMRC offers simplified “Three Line Account” reporting if your turnover is under £85,000 — just enter total income, total expenses, and net profit.
For turnover over £85,000, you must provide a full breakdown of income and expense categories.
5
Complete Any Additional Sections
Add any other income sources: employment income, rental income, dividends, savings interest, capital gains. Claim any reliefs you’re entitled to: pension contributions, Gift Aid, marriage allowance, loss relief.
6
Review Your Tax Calculation
HMRC’s system automatically calculates your tax liability. Review the breakdown carefully. Check that your income and expenses look correct. If the figure seems much higher or lower than expected, review your entries for errors before submitting.
7
Submit and Save Your Confirmation
Click submit. HMRC will immediately issue a confirmation reference — save or print this as proof of submission. Your return is now filed.
Step 4 — Pay Your Tax Bill
Filing and paying are separate steps. After filing, you must also pay any tax owed by the deadline. Here’s how payments work:
📅
31 January — Balancing Payment
Pay any remaining tax owed for the previous tax year, plus your first Payment on Account for the current year (50% of last year’s bill).
📅
31 July — Second Payment on Account
Pay the second instalment (another 50% of last year’s bill) as an advance payment toward your current year’s tax.
📅
Following 31 January — Final Balancing
If your actual tax for the year differs from the Payments on Account made, you pay the difference (or receive a repayment).
How to pay HMRC
- Bank transfer (Faster Payments) — recommended, instant
- Online or telephone banking
- CHAPS (for same-day payments)
- Direct Debit (must be set up in advance)
- Cheque (allow 3 working days)
Penalties for Late Filing or Payment
| Failure | Penalty |
|---|---|
| 1 day late (missing 31 January deadline) | £100 automatic fine |
| 3 months late | £10 per day (up to 90 days = £900) |
| 6 months late | Additional £300 or 5% of tax due (whichever is higher) |
| 12 months late | Further £300 or 5% of tax (whichever is higher) |
| Late payment (30 days) | 5% of unpaid tax |
| Late payment interest | Bank base rate + 2.5% per annum |
Frequently Asked Questions
What if I can’t pay my tax bill?
Contact HMRC before the deadline — do not ignore it. HMRC offers a Time to Pay arrangement that allows you to pay your tax bill in instalments. You must set this up before the payment deadline (31 January) to avoid late payment penalties. You can arrange this online if you owe less than £30,000.
Can I amend my return after submitting?
Yes. You can amend a submitted Self Assessment return within 12 months of the 31 January filing deadline. Log into your Government Gateway account, access your return, and make the amendments. You must also notify HMRC if you discover an error after this 12-month window.
What records do I need to keep?
HMRC requires you to keep supporting records for at least 5 years after the 31 January deadline for that tax year. This includes all income records, expense receipts, bank statements, and any supporting documentation for deductions claimed.