If you are self-employed, landlord, or have untaxed income, you are probably familiar with the Self-Assessment tax return. But every year, many taxpayers leave their filing to the last minute, sometimes missing deadlines and facing penalties. With the 2024/25 tax year underway, it’s a perfect time to get ahead of the game.

In this blog, we’ll break down the important Self-Assessment deadlines for the 2024/25 tax year, why submitting early is a smart move, and what you need to prepare for your return.

Who Needs to Complete a Self-Assessment Tax Return?

Before diving into the deadlines, let’s clarify who needs to file a Self-Assessment return. You will typically need to file during the 2024/25 tax year (6 April 2024 to 5 April 2025)

• Were self-employed or a sole trader
• Earned more than £1,000 from self-employment
• Received rental income over £1,000
• Had untaxed income (e.g., dividends, investments, or savings interest)
• Were a partner in a business partnership
• Claimed Child Benefit and your income was over £50,000
• Earned income abroad or from foreign investments
• Had income over £100,000

If any of these apply to you, HMRC expects you to submit a Self-Assessment tax return and failure to do so can lead to fines and interest charges.

Key Self-Assessment Deadlines for 2024/25

Let’s look at the key deadlines for the 2024/25 Self-Assessment cycle:

6 April 2025 – Start of Filing Period

You can begin submitting your tax return for the 2024/25 tax year from this date. Although most people wait until closer to the deadline, you don’t have to. Submitting early has several advantages, which we’ll explore shortly.

31 October 2025 – Paper Return Deadline

If you plan to file a paper tax return, HMRC must receive it by midnight on 31 October 2025. It’s worth noting that paper returns are becoming less common, and HMRC encourages most people to file online instead.

31 January 2026 – Online Return & Payment Deadline

This is the main deadline on 31 January 2026

• Submit your online Self tax return for 2024/25
• Pay any tax you owe
• Pay your first payment on account (if applicable) for the 2025/26 tax year

Missing this deadline results in an automatic £100 fine, even if you don’t pay any tax.

What Happens If You Miss the Tex Deadline?

If you don’t  pay your Self-Assessment tax on time, HMRC will issue penalties:

• Late Filing:
  

  • £100 automatic fine after missing the deadline
  • Additional daily penalties (£10 per day up to 90 days)
  • Further penalties at 6 and 12 months if still outstanding

• Late Payment:
  

  • Interest in the unpaid tax
  • 5% surcharge on unpaid amounts after 30 days
  • Further 5% surcharges at 6 and 12 months

These penalties can speedily add up so timely submission is essential.

Why You Should File Early

Even though the final deadline is 31 January 2026, there are several benefits to submitting your return much earlier:

1. Peace of Mind

Avoid the January rush and reduce stress. Filing early means you won’t be scrambling to gather receipts and invoices during the busiest part of the year.

2. More Time to Pay

The earlier you know how much tax you owe, the more time you must budget. You can still wait until January to make the payment, but you’ll avoid any surprises.

3. Get Tax Refunds Sooner

If you’re due to a refund (for example, if you’ve overpaid tax or had work expenses), HMRC will process it as soon as your return is submitted, no need to wait until January.

4. Avoid Last-Minute Errors

Rushed submissions often lead to mistakes. Filing early gives you time to double check everything or seek professional advice if needed.

5. More Accountant Availability

If you use an accountant, they’re often less busy outside of January. You’re more likely to get quicker, personalized support earlier in the year.

What Information Do You Need to Complete Your Tax Return?

To file your 2024/25 return, make sure you have:

• Your Unique Taxpayer Reference (UTR) and National Insurance number
• Details of all income earned between 6 April 2024 and 5 April 2025
• Business expenses (for sole traders)
• Rental income and allowable property expenses (for landlords)
• Dividends and savings interest
• Contributions to pensions or charitable donations
• Records of any capital gains
• Previous year’s tax return (for reference)
• Any tax reliefs or deductions you plan to claim

Registering for Self Assessment

If you are new to Self-Assessment for instance, you became self-employed or started renting out a property during the 2024/25 tax year, you must register with HMRC before you can submit a return.

Self-employed?

You must register by 5 October 2025.

You can register online via HMRC’s website. Once registered, you’ll receive your UTR (Unique Taxpayer Reference), which is needed to file your return.

Payments on Account – What You Need to Know

If your tax bill is over £1,000 and less than 80% of your tax is deducted at source (e.g., via PAYE), HMRC may ask you to make payments on account.

These are advance payments toward your next year’s tax bill:

• The first payment is due on 31 January (along with your main tax bill)
• Second payment is due on 31 July

Each payment is typically half of your previous year’s tax bill.

What If You Can’t Afford to Pay?

If you know you’ll struggle to pay your tax bill by 31 January, don’t wait until the deadline. Contact HMRC early to arrange a Time to Pay plan. This lets you spread your tax bill into affordable monthly payments, but interest may apply.

Final Tips for Filing Your Self Assessment Return

• Go digital: Filing online is faster, easier, and gives you access to automatic calculations and submission receipts.
• Keep records: Maintain digital records of all income and expenses this will be mandatory when Making Tax Digital for Income Tax comes into effect in 2026.
• Double-check before submitting: Make sure figures are correct and all required sections are completed.
• Don’t ignore HMRC letters: They may include deadlines, payment requests, or follow-up information.

 Summary

The key Self Assessment dates for 2024/25 are:

• 6 April 2025 – Start of the filing period
• 31 October 2025 – Paper return deadline
• 31 January 2026 – Online return and payment deadline
• 5 October 2025 – Deadline to register if new to Self-Assessment

While 31 January 2026 might feel far off, filing early can save you stress, prevent mistakes, and help you manage your cash flow better. Whether you’re a sole trader, landlord, or freelancer, being proactive about your Self-Assessment is one of the smartest financial decisions you can make.