Self-Assessment is Coming: Do You Need To Register For October?

With just weeks left until the 5 October self-assessment registration deadline and not long until the January 31st submission deadline, thousands of people across the country are about to discover they’ve left their self-assessment dangerously late. 

If you’re reading this in a mild panic, wondering whether you need to file a tax return this year, you’re not alone.

Really, self-assessment catches more people than you’d expect. It’s not just the self-employed who need to worry about it.

Company directors, landlords, high earners, and anyone with untaxed income could find themselves facing penalties if they don’t act fast.

Let’s cut through the confusion and get you sorted before it’s too late.

The October Deadline

If you’ve never submitted a self-assessment tax return before, you must register by 5 October 2025 to submit a return for the 2024-25 tax year. That’s October 5th – exactly two weeks away.

The registration process itself takes time. You need to get your Unique Taxpayer Reference (UTR) number and activation code, which can take weeks to arrive by post. This isn’t something you can sort out on 4 October and hope for the best. 

Even if you submit your registration on the deadline day, you might not receive your login details in time to actually file your return by January.

Do You Need to File?

Many people assume self-assessment is only for the self-employed, but that’s a dangerous misconception. The rules are broader than most people realise, and the consequences of getting it wrong can be expensive.

You need to file a self-assessment if you fall into any of these categories:

The obvious ones:

• You’re self-employed and earned more than £1,000 in the 2024/25 tax year
• You’re a partner in a business partnership
• You’re a company director (even if you didn’t take a salary)

The less obvious ones:

• Your total income exceeded £100,000, even if you’re employed and pay tax through PAYE
• You received more than £2,500 in rental income before expenses
• You had untaxed income above £2,500 from investments, savings, or dividends
• You received Child Benefit and either you or your partner earned over £60,000
• You want to claim tax relief on pension contributions that weren’t automatically applied

The £100,000 threshold catches many people off guard. Even if you’re employed and your employer handles all your tax through PAYE, earning over £100,000 means you start losing your personal allowance and must file a return. 

This includes bonuses, benefits in kind, and any other income – it all counts towards that threshold.

The 2025 Timeline You Need to Know

Getting registered by 5 October is just the beginning. Here’s what happens next, and why understanding the full timeline matters for your planning:

• 31 October 2025: Deadline for paper returns. Don’t even think about going down this route unless you absolutely have to. Paper returns have an earlier deadline and offer none of the convenience of online filing. Plus, if you make an error on a paper return, correcting it becomes a much more complicated process.
• 30 December 2025: If you file your return online and also have earnings taxed through PAYE, you can opt to have any tax owed collected via your tax code throughout the following year. This only works if you owe less than £3,000 and can be a helpful way to spread the cost instead of facing a large lump sum payment.
• 31 January 2026: The big one. This is when online returns are due and when you need to pay any tax owed. It’s also when your first payment on account for the following year becomes due if you owe more than £1,000. This double payment requirement often catches people unprepared.
• 31 July 2026: Second payment on account deadline. This completes your advance payments for the 2025/26 tax year.

The Cost of Getting It Wrong

HMRC’s penalty system is clear and escalates quickly. What starts as a relatively small penalty can snowball into a significant financial burden if left unaddressed:

Late filing penalties:

• £100 immediate penalty for missing the 31 January deadline, even if you don’t owe any tax
• After 3 months: £10 per day for up to 90 days (maximum £900)
• After 6 months: 5% of tax owed or £300, whichever is greater
• After 12 months: another 5% of tax owed or £300, whichever is greater

Late payment penalties:

• 5% of unpaid tax at 30 days late
• 5% of unpaid tax at 6 months late
• 5% of unpaid tax at 12 months late
• Interest charged on unpaid tax from day one

If you register after 5 October and don’t pay all your tax by 31 January, you may face an additional “failure to notify” penalty based on the amount you still owe. 

This penalty is calculated as a percentage of the tax that should have been paid, making it particularly expensive for those with significant tax liabilities.

Getting Your Documents Together

The 2024/25 tax year ran from 6 April 2024 to 5 April 2025. You’ll need records of all income and expenses during this period. Starting your document gathering now, while the year is still relatively fresh in your memory, can save hours of detective work later.

Essential documents include:

• P60 from your employer
• P45s if you changed jobs
• Bank statements showing interest earned
• Dividend vouchers or statements
• Rental income records and associated expenses
• Business income and expense records if self-employed
• Records of any other untaxed income

Don’t forget about allowable expenses. If you’re self-employed, working from home, or have business-related costs, these can reduce your tax bill significantly. 

Keep receipts for everything from office supplies to professional subscriptions. Even small amounts add up, and proper record-keeping can make a meaningful difference to your final tax calculation.

The Payments on Account Trap

If your tax bill exceeds £1,000, HMRC will expect payments on account for the following year. These are advance payments based on your current year’s liability, paid in two instalments on 31 January and 31 July.

Many people get caught out by this. You file your return in January, discover you owe £3,000 for the year just ended, and then realise you also need to pay £1,500 as your first payment on account for the current year. That £4,500 total can come as a nasty shock if you’re not prepared.

The logic behind payments on account is that if you owed tax this year, you’ll probably owe similar amounts next year. While you can reduce these payments if your income drops, many people forget this option and overpay unnecessarily.

Making Tax Digital (MTD) is Coming

While it doesn’t affect this year’s return, significant changes are on the horizon. Sole traders and landlords with qualifying income over £50,000 will be required to use Making Tax Digital for Income Tax (MTD for ITSA) from April 2026.

MTD means you’ll need to:

• Keep digital records of your income and expenses
• Use HMRC-approved software to maintain these records
• Submit quarterly updates to HMRC throughout the year
• File a final annual return

This represents a big change from the current system where you only need to file once a year. Instead of gathering everything in January, you’ll be updating HMRC every three months.

The threshold will drop to £30,000 in April 2027, bringing even more people into the digital reporting system.

Read our full guide to MTD for ITSA here.

Your September Action Plan

With the clock ticking, here’s what you need to do right now:

This week:

1. Use HMRC’s online checker tool to confirm whether you need to file
2. If you do, register immediately for self-assessment
3. Start gathering all your financial documents
4. Create a dedicated folder (physical or digital) for all tax-related paperwork

Next week:

1. Chase any missing documents from employers, banks, or investment providers
2. Start calculating your likely tax liability
3. If you’re using an accountant, get your documents to them immediately
4. If you’re doing it yourself, familiarise yourself with the online system

Don’t wait until January! The January deadline is for submission and payment, but there’s nothing stopping you from filing much earlier. 

Many experienced self-assessment filers complete their returns in the autumn when they have time to think clearly and chase any missing information. 

When to Get Professional Help

Self-assessment can be straightforward if your affairs are simple, but it becomes complex quickly. The tax system has numerous nuances that can trip up even careful individuals, and the cost of getting it wrong often exceeds the cost of professional advice.

Consider professional help if you’re dealing with:

• Multiple income sources
• Business expenses and allowable deductions
• Rental properties
• Capital gains from asset sales
• Pension contribution planning
• First-time filing uncertainty

The cost of an accountant is often offset by the time saved, stress avoided, and potential tax savings they can identify. 

At Double Point, we’ve guided countless clients through their first self-assessment and helped established filers optimise their tax position. We understand that tax can feel overwhelming, especially when deadlines are looming and the consequences of mistakes can be expensive.

Whether you need help determining if you should file, want someone to handle the entire process, or simply need advice on maximising your allowable expenses, we’re here to help. 

Don’t let the October deadline catch you unprepared – get in touch for a consultation and let us take the stress out of your self-assessment.