If you’re self employed, a landlord or have untaxed income, you’ll need to complete a self assessment tax return. But when is self assessment due? Getting familiar with deadlines is critical for maintaining compliance, avoiding penalties, and keeping your financial management in check.
In this guide, we’ll take you through the key self assessment tax deadlines, what happens if you miss them, and how you can stay on top of your return.
The Importance of Meeting Self Assessment Deadlines
Failing to submit a self assessment in time can trigger automatic penalties, interest charges, and make stress levels peak, especially if HMRC begins to pepper you with reminders or even investigations. Meeting deadlines helps:
- Avoid fines and late payment charges
- Keep your financial records up to date
- Stay in control of your cash flow
- Reduce the risk of HMRC scrutiny
Whether you are filing for the first time or have done this in the past, understanding when self assessments are due is an essential part of the process that helps you keep one step ahead.
The Key Deadlines for the New Tax Year:
In the UK, a tax year runs from April 6th to April 5th the year after. Here’s what you need to know about the key self assessment deadlines:
6th April
The new tax year begins. You can do this from this date; preparing your self assessment tax return for the previous tax year. So, for example, you can start submitting your 2024/25 tax return on 6th April 2025.
If you’re trying to file early and not waiting until the last moment, now is the ideal moment to get your income, expenses and other financial papers all together.
31st July
This is the deadline for the second payment on account if you’re required to make advance payments toward your tax bill. Payments on account are made against your previous year’s tax bill and are intended to spread the cost.
You may need to make a payment on 31st July if:
- Your last tax bill was over £1,000
- Less than 80% of your tax was collected via PAYE
If your actual tax liability comes in less than the sum of the two previously paid payments on account, HMRC will refund the difference. Also, if your expected tax liability for the following year is going to significantly drop, we can ask HMRC to adjust the payments on account.
5th October
If you’ve never filed a self assessment, this is your deadline to register with HMRC for the first time. You’ll need to do this if you’ve begun earning untaxed income (e.g. from self-employment or property rental), or if you earn over £100k on PAYE.
Late registration may incur penalties and delays in accessing your online account. You should do it as soon as possible to get your Unique Taxpayer Reference (UTR).
31st October
This is the deadline for paper filing. If you’re reporting via a paper tax return rather than filing electronically, it needs to be received by HMRC by midnight on 31st October.
Most people file online because it gives you until January and is processed faster, but if you like paper, this is your deadline.
31st January
The main self assessment deadline. This is the final date to:
- Submit your online tax return for the previous tax year
- Pay any tax you owe
- Make your first payment on account for the current year, if applicable
For example, by 31st January 2026, you must file and pay your 2024/25 return. Miss this date, and penalties start automatically.
Understanding Self Assessment
Self assessment is how people report income and pay tax to HMRC if it’s not automatically deducted, for example, through PAYE.
Who needs to complete a self assessment tax return?
You’ll need to file a self assessment tax return if you:
- Are self-employed as a sole trader and earned more than £1,000
- Are a partner in a business partnership
- Earn untaxed income (e.g. rent, dividends, foreign income)
- Are a company director (unless it’s a non-profit or no income)
- Earn over £100,000 annually
- Claim child benefit but your income is over £50,000
- Need to claim tax relief (e.g. for pension contributions or expenses)
If in doubt, check with HMRC or a tax professional—failing to submit a return when you should can be costly.
What Happens if you Miss the Self Assessment Tax Deadline?
Penalties for missing the filing deadline
HMRC will automatically issue you with a £100 fine (even if you owe no tax) if you miss the 31st January filing deadline. Should the return still not be submitted, more penalties kick in:
- 3 months late: £10 per day (up to 90 days, £900 max)
- 6 months late: £300 or 5% of the tax due (whichever is higher)
- 12 months late: An additional £300 or 5% of the tax due, and possibly more if HMRC believes you’re deliberately avoiding payment
Late payment penalties and interest charges
If you miss the 31st January payment deadline:
- 30 days late: 5% of the unpaid tax
- 6 months late: Another 5%
- 12 months late: Yet another 5%
In addition to these, interest accrues daily on any unpaid amounts.
How penalties increase over time
What might start as a £100 fine can quickly snowball into hundreds or even thousands of pounds if the return and payment remain overdue. For example:
- A return filed six months late with unpaid tax could cost £1,600+ in penalties alone
- Add interest, and the total could rise even more
The longer you leave it, the worse it gets. That’s why knowing when the self assessment tax deadline is can save you from serious financial pain.
Special Circumstances
Extensions and reasonable excuses
HMRC may cancel or reduce penalties if you have a reasonable excuse, such as:
- A serious illness or hospital stay
- Bereavement
- Technical failures when submitting
- Fire, flood, or theft affecting records
Extensions are rare, but during exceptional events (like the COVID-19 pandemic), HMRC has offered grace periods.
If you believe you have a valid reason, contact HMRC as soon as possible.
Self assessment when leaving the UK
Even if you move abroad or cease to be regarded as a UK tax resident, you may need to submit a tax return for the year in which you departed. But use form P85 to inform HMRC and declare UK income you still receive.
Unsure whether to file after you move? A cross border tax advisor can help you with your cross-border tax obligations.
How to File your Self Assessment Tax Return
Here are the basic steps to complete your self assessment:
- Register for self assessment with HMRC (if it’s your first time)
- Get your UTR and set up your online account
- Keep records of income and expenses throughout the year
- Log in to HMRC’s online system or use approved software
- Fill in the return accurately with income, expenses, and other details
- Submit your return by 31st January
- Pay your tax bill by the same deadline
Filing online gives you more time, calculates your bill automatically, and allows you to save progress as you go.
How Reed & Co. can Help
Worried about filing on time? Unsure about what you can claim or whether you need to register? Reed & Co. has a network of expert tax professionals ready to support you with:
- Self assessment preparation and filing
- Guidance on allowable expenses
- Advice on payments on account
- Support with HMRC correspondence
We take the stress out of tax season so you can focus on running your business or managing your income confidently.
Avoid penalties and stay ahead of the self assessment tax deadline. Contact Reed & Co. today and let our experts handle your return—accurately, on time, and hassle-free.
