Self Assessment Tax Return Deadlines Explained (2026/27)
Missing a Self Assessment deadline can lead to unnecessary penalties and interest from HMRC. The good news is that, with a little planning, it's easy to stay on top of your obligations.
Whether you're self-employed, a landlord, a company director or have other income to declare, this guide explains the key Self Assessment deadlines, what they mean and what you need to do.
Who Needs to Complete a Self Assessment Tax Return?
You may need to complete a Self Assessment tax return if you:
Are self-employed.
Receive rental income from property.
Have untaxed income.
Need to report Capital Gains Tax.
Receive certain investment or overseas income.
Have been asked by HMRC to complete a tax return.
If you're unsure whether you need to file, it's worth checking before the deadline to avoid potential penalties.
The Key Self Assessment Deadlines
For most taxpayers, there are just three dates to remember. If you're completing a tax return for the tax year 6 April 2025 to 5 April 2026, your key deadlines are:
5 October 2026 – Register for Self Assessment (first-time filers only).
31 January 2027 – Submit your online tax return and pay any tax due.
31 July 2027 – Make your second Payment on Account (if required).
Most Self Assessment tax returns are now submitted online. A separate 31 October deadline applies only if you chose to submit a paper tax return by post, which is now uncommon.
What Are Payments on Account?
Many people are surprised when their first Self Assessment tax bill is larger than expected.
This is because HMRC may ask you to make Payments on Account towards your next year's tax bill.
Who Do Payments on Account Apply To?
Payments on Account usually apply if:
Your Self Assessment tax bill is more than £1,000, and
Less than 80% of your tax has already been collected through PAYE or another source.
If your Self Assessment tax bill is £1,000 or less, or most of your tax has already been deducted before you receive it, you will not normally have to make Payments on Account.
A Simple Example
Imagine you've completed your 2025/26 Self Assessment tax return. The return calculates that you owe £8,000 in tax.
Because your tax bill is over £1,000, HMRC may ask you to make Payments on Account towards your 2026/27 tax bill.
31 January 2027: Tax due for 2025/26 - £8,000
31 January 2027: First Payment on Account for 2026/27 - £4,000
Total due on 31 January 2027- £12,000
31 July 2027: Second Payment on Account for 2026/27 - £4,000
Although your tax return calculated a tax bill of £8,000 for the 2025/26 tax year, HMRC is also asking you to pay half of your estimated tax for the following year in advance.
When you later submit your 2026/27 tax return, HMRC compares the tax you've already paid with the amount actually due:
If you've paid too much, you'll normally receive a refund or have the overpayment set against future tax.
If you've paid too little, you'll simply pay the difference.
Craigerne Tip: We encourage clients to prepare their tax return well before January. Knowing your tax bill early gives you time to budget for any Payments on Account and avoids last-minute surprises.
What Happens If You Miss a Deadline?
Missing a deadline can become costly.
HMRC may charge:
An immediate £100 late filing penalty.
Additional daily penalties if your return remains outstanding.
Further penalties for prolonged delays.
Interest on any late tax payments.
Submitting your return as early as possible is the best way to avoid unnecessary penalties and stress.
What Information Will You Need?
Having your paperwork ready makes completing your tax return much easier.
Depending on your circumstances, you may need:
Employment income (P60 or P45).
Self-employment income and expenses.
Rental income and expenses.
Bank interest.
Dividend income.
Pension contributions.
Gift Aid donations.
Capital Gains information.
Keeping organised records throughout the year can save considerable time when your tax return is due.
Common Mistakes We See
Some of the most common issues include:
Leaving everything until January.
Forgetting to register for Self Assessment.
Missing allowable business expenses.
Forgetting rental or dividend income.
Losing receipts and records.
Underestimating the first tax bill because of Payments on Account.
Getting advice early can often save both tax and stress.
Top Tips
Register early if this is your first tax return.
Keep digital records throughout the year.
Don't wait until January to gather your paperwork.
Set money aside regularly for your tax bill.
How Craigerne Accountancy Can Help
At Craigerne Accountancy, we help individuals, landlords and business owners complete accurate Self Assessment tax returns on time.
We can help you:
Prepare and submit your tax return.
Claim all allowable expenses and tax reliefs.
Understand your tax bill before it's due.
Help you budget for Payments on Account.
Deal with HMRC on your behalf if required.
Whether it's your first tax return or you've been filing for years, we'll make the process straightforward, accurate and stress-free.