Self-Assessment Deadline Tips: Avoid Last-Minute Panic
By Sardar Muhammad, AAT • • 8 min read
⏰ The Deadline: 31st January 2026
For the 2024/25 tax year, your online self-assessment must be submitted and tax paid by 11:59pm on 31st January 2026. Don't wait until the last minute!
Why You Shouldn't Leave It Until January
Every year, millions of people file their tax return in the final week of January. In 2024, over 60,000 people filed on deadline day itself – with many experiencing website crashes and stress.
Here's why you should file early:
- ✅ Know what you owe well in advance
- ✅ Time to save up for payment
- ✅ Avoid website crashes on deadline day
- ✅ Get your refund faster (if owed)
- ✅ Spot missing documents early
- ✅ Reduce stress and anxiety
- ✅ Time to fix any errors
Key Self-Assessment Deadlines
| Date | Deadline |
|---|---|
| 5th April 2025 | End of 2024/25 tax year |
| 5th October 2025 | Register for self-assessment (if new) |
| 31st October 2025 | Paper tax return deadline |
| 31st January 2026 | Online tax return + payment deadline |
| 31st July 2026 | Second payment on account |
Penalties for Missing the Deadline
HMRC's penalty system escalates quickly:
1 day late
Automatic £100 penalty – even if you owe no tax
3 months late
£10 per day for up to 90 days (£900 maximum)
6 months late
£300 or 5% of tax owed (whichever is greater)
12 months late
Another £300 or 5% (serious cases: 100% of tax)
Plus, late payment incurs interest (currently 7.75%) on unpaid tax.
What You Need to Prepare
Gather these documents before you start:
📄 Income Documents
- P60 (if employed)
- P45 (if you left a job)
- P11D (benefits in kind)
- Self-employment income records
- Bank interest statements
- Dividend vouchers
- Rental income records
- CIS statements (construction workers)
📋 Expense Records
- Business expenses receipts
- Mileage logs
- Home office costs
- Professional subscriptions
- Insurance premiums
🔐 HMRC Details
- Government Gateway login
- Unique Taxpayer Reference (UTR)
- National Insurance number
Top 10 Self-Assessment Tips
- Start in April – keep records from day one
- Use accounting software – track income and expenses automatically
- Set money aside – save 20-30% of profits for tax
- Claim all expenses – every legitimate expense reduces your bill
- Keep receipts – digital photos are fine
- Check your tax code – wrong codes mean wrong tax
- Don't forget gift aid – get tax relief on donations
- Consider pension contributions – reduce taxable income
- File early – know what you owe sooner
- Get professional help – it's often worth the cost
What If You Can't Pay?
If you can't pay your tax bill by 31st January, don't panic. Options include:
- Time to Pay arrangement – spread payments over up to 12 months
- Pay what you can – partial payment reduces interest
- Contact HMRC early – before the deadline if possible
Important: Always file on time, even if you can't pay. The filing penalty is separate from the payment penalty.
Frequently Asked Questions
When is the self-assessment deadline?
The online self-assessment deadline is 31st January following the end of the tax year. For the 2024/25 tax year (ending 5th April 2025), the deadline is 31st January 2026.
What happens if I miss the deadline?
You'll receive an automatic £100 late filing penalty, even if you owe no tax. After 3 months, you face daily penalties of £10 (up to £900). After 6 months, an additional 5% of tax owed. After 12 months, another 5%.
Can I get an extension on my tax return?
HMRC rarely grants extensions. In exceptional circumstances (bereavement, serious illness), you may be able to appeal a penalty. But it's always better to file on time, even if incomplete.
Need Help With Your Tax Return?
Don't wait until January. Let me prepare your self-assessment early – stress-free and accurate.
Sardar Muhammad, AAT Certified
Sardar is an AAT certified accountant and founder of LimeTree Accounting Solutions in Glasgow. He helps self-employed individuals and small businesses file accurate tax returns on time.