If you earn extra money or are self-employed, pay attention. HMRC has issued a serious warning about Self Assessment, and the October 5 deadline is important for many in the UK. If you’ve never filed a tax return before but need to now, you must register for Self Assessment by October 5, 2025. Not doing this could result in a penalty.
At Clarkwell & Co., our accountants in London are helping clients meet this urgent deadline. We understand that HMRC’s rules can be confusing, especially for those balancing jobs, side businesses, or rental income. That’s why we created this guide to help you understand your responsibilities and avoid fines. Here’s what you need to know and do quickly.
Why This October 5 Deadline Matters More Than Ever
The 5th of October is an important date. It’s the last day to register for Self Assessment with HMRC if you earned untaxed income last year and haven’t registered before. This is not about filing your tax return, which happens later. It’s about informing HMRC that you have tax to report for the 2024–2025 tax year.
If you’re a new sole trader, freelancer, landlord, or have received dividends or foreign income, don’t miss this deadline. If you do, you could face a penalty for not notifying HMRC. Even small or irregular earnings must be reported on time.
HMRC is enforcing rules more strictly now, especially for digital platform earnings and cross-border income. Ignoring this deadline can lead to significant risks. In 2024, many UK residents faced penalties just for missing registration, even if they owed little tax.
Who Needs to Register for Self Assessment?
It’s important to know who needs to register for Self Assessment. Many people don’t realise they qualify. If you fit any of these categories, take action now:
- You are self-employed and earned over £1,000 in the tax year.
- You were in a business partnership.
- You earned rental income from property, even from one tenant.
- You received untaxed dividends, interest, or savings income.
- You earned foreign income that was taxed abroad.
- You sold assets like shares or property and owe Capital Gains Tax.
- You faced the High Income Child Benefit Charge.
In today’s gig economy, many people unknowingly fall into these categories. Delivering food part-time, selling on eBay, tutoring students, or renting out a spare room can all count as untaxed income. If you’re unsure, use HMRC’s eligibility checker or consult a qualified accountant. At Clarkwell & Co., we provide accounting services for sole traders and small businesses to help you meet your tax obligations.
What Happens If You Miss the October 5 Deadline?
If you don’t register with HMRC by October 5, you could face a penalty for failing to notify them. This is different from penalties for filing late. HMRC wants you to communicate with them, and if they think you should have registered but didn’t, they may take quick action.
Penalties depend on how much tax HMRC thinks you owe and whether your failure to register was intentional, careless, or reasonable. Even if you didn’t mean to miss the deadline, HMRC may still penalise you unless you can show that you took care to meet the requirements.
Penalties can be anywhere from 0% to 100% of the tax owed. For example, if HMRC thinks you owe £2,000 in tax, your penalty could also be £2,000. That’s why it’s important to act now, especially since more Late Self Assessment penalties are being reported across the UK.
How to Register for Self Assessment UK: Step-by-Step
If you need to register, here’s how to do it quickly:
- Go to the HMRC website and create a Government Gateway account.
- Fill out the SA1 form online to register for Self Assessment.
- HMRC will mail you a Unique Taxpayer Reference (UTR) number within 10 working days.
- After you get your UTR, you can log in and complete your HMRC tax return for 2025 online.
Register early to avoid delays. HMRC may get busy near the deadline, which could cause you to miss important documents for filing. Registering now gives you time to prepare and reduces stress.
If you feel overwhelmed or don’t know where to start, our Self Assessment tax specialists in London can manage the whole process for you, from registration to final submission.
Common Misconceptions About Self Assessment
One dangerous assumption is, “I don’t need to file a tax return because I didn’t make much money.” This is wrong. If you earn more than £1,000 from self-employment, you must register and file with HMRC.
Another myth is, “HMRC will contact me if I need to file.” This is also incorrect. It’s your responsibility to inform HMRC if you think you need to file. Don’t wait for them to reach out. HMRC penalties apply to both innocent mistakes and intentional hiding of income, leading to heavy fines.
Other common misconceptions are:
“I can file whenever I want.” This is false; you must file by the deadline to avoid penalties.
“If I don’t owe tax, I don’t need to file.” This is also incorrect; you need to file based on your income, not just what you owe in tax.
Don’t let these myths lead to penalties for failing to notify HMRC. Our accounting services can help clarify your responsibilities and keep you protected.
Untaxed Income? Here’s What You Need to Know
Not all income is taxed automatically. If you have earned untaxed income, it may come from:
- Airbnb or short-term rentals
- Selling online on Etsy, eBay, Depop, or Vinted
- Freelance work, such as graphic design, writing, or tutoring
- Consulting, coaching, or mentoring
- Profits from cryptocurrency or NFT trades
- Side jobs like drop-shipping or affiliate marketing
If you earn from these sources, you may need to file a Self Assessment for untaxed income. Even small amounts can push you over the income limit. This applies even if you have a regular PAYE job. Clarkwell & Co. can help you identify all your income and make sure nothing is missed.
Penalties Explained: What You Could Owe
HMRC has a tiered penalty system. Here’s a simpler breakdown:
- If you miss the registration deadline of October 5, you may face a “failure to notify” penalty of 0%–100% of your owed tax.
- If you file your return late, you will get a £100 initial penalty.
- If you are more than three months late, you could incur daily penalties up to £900 (£10 per day).
- If you’re over six months late, you’ll face an extra 5% of the tax due or a minimum of £300.
- If you’re over twelve months late, you could get another 5% or more, based on HMRC’s review.
These penalties can total over £1,600 before you even pay your tax. HMRC is getting stricter, especially with new digital income. It’s not worth the risk. If HMRC is already contacting you or reviewing your case, our Self Assessment tax investigation service can help reduce penalties and support you.
Why It Pays to Use a Professional Accountant
Handling self-assessment on your own can be risky, especially if you’re new to it. The process can be complicated, especially with multiple income sources, foreign income, or recent life changes like marriage, buying a house, or starting a side business.
At Clarkwell & Co., our professional accountants do more than just file your tax return. We:
- Find tax-saving opportunities you might not know about
- Help you avoid penalties for registration and filing
- Ensure you follow the latest HMRC rules
- Provide documents ready for audits if needed
- Give strategic advice for future tax years
Whether you’re a sole trader, freelancer, or small business owner, our accountants in London will give you peace of mind, save you time, and improve your financial results.
Proactive Steps You Can Take Today
Here’s a simple action plan to help you stay on track:
- Use HMRC’s online tool to see if you need to register.
- Collect all your income records (from jobs, freelancing, property, crypto, and dividends).
- Register on HMRC’s portal before October 5, 2025.
- Set reminders for the filing and payment deadlines on January 31 and October 31.
- Check available tax reliefs and allowances, like the marriage allowance and work-from-home expenses.
- Reach out to a tax expert for help with your return.
Need help? Our London Self Assessment experts are ready to assist you. We help many clients each year meet deadlines, avoid penalties, and improve their returns. Act soon for more options!
Don’t Let Time (or HMRC) Catch You Out
The Self Assessment deadline in 2025 is coming soon, so you need to act fast. If you have a side job, earn rental income, or are self-employed, you must register with HMRC by October 5.
Delaying could lead to more than just extra costs; it can create stress and confusion in your busy life. But you don’t have to do this alone.
At Clarkwell & Co., we offer complete accounting services for individuals, sole traders, and small businesses throughout London and the UK. We can help you stay compliant, save on taxes, and avoid mistakes.
