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.

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.

• Are a partner in a business partnership.

• Need to claim specific tax reliefs or allowances.

• Have been asked by HMRC to complete a tax return.

Important: A high salary on its own no longer automatically means you need to complete a Self Assessment tax return. If all of your income is taxed through PAYE, you may not need to file a return unless HMRC requests one or you have other income to report.

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 are 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 for the 2025/26 tax year. This is also the deadline for your first Payment on Account for 2026/27 (if applicable).

• 31 July 2027 – Make your second Payment on Account (if applicable).

Most Self Assessment tax returns are now submitted online. A separate 31 October deadline applies only to paper tax returns. If you're eligible to have tax collected through your PAYE tax code, you'll normally need to file online by 30 December.

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 assumes you will earn a similar amount next year and will ask for payments in advance:

• 31 January 2027: Balancing 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 in advance 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 remaining balance.

Can Payments on Account be reduced?

If you expect your tax bill to be lower than the previous year, you may be able to reduce your Payments on Account. Take care not to reduce them too far, as HMRC may charge interest if you underpay.

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 Self Assessment deadline can quickly become costly. HMRC enforces a strict, escalating penalty regime for late filing and late payments—even if you ultimately owe no tax at all. 

Here is exactly how the penalties stack up if you miss the 31 January deadline:

• 1 day late: An immediate £100 automatic penalty applies the moment you miss the midnight deadline.

• 3 months late: HMRC charges an additional £10 per day for up to 90 days, adding a maximum of £900 to your bill.

• 6 months late: A further penalty of 5% of the tax due or £300 (whichever is greater) is added.

• 12 months late: Another 5% of the tax due or £300 (whichever is greater) is applied. In serious cases, the fine can be up to 100% of the tax due. 

Late Payment Penalties and Interest

Filing your tax return on time is only part of the process—you also need to pay any tax due by the deadline.

If payment is made late, HMRC will charge interest on the outstanding amount from the day after the payment deadline. Depending on your circumstances and which penalty regime applies, HMRC may also charge late-payment penalties if the tax remains unpaid. 

If you're struggling to pay, it's important to contact HMRC as soon as possible. In many cases, agreeing a Time to Pay arrangement before penalties arise can help reduce or avoid some late-payment penalties. 

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.

Making Tax Digital for Income Tax: What You Need to Know

Making Tax Digital (MTD) for Income Tax is now being introduced by HMRC.

If you're self-employed or a landlord, it's important to understand whether the new rules apply to you and what you need to do before your start date.

The good news is that, with the right software and a little preparation, the transition is usually straightforward.

What is Making Tax Digital?

MTD is HMRC's programme to modernise the UK tax system.

Instead of keeping paper records and completing one annual Self Assessment tax return, affected taxpayers will:

• Keep digital accounting records.

• Use HMRC-compatible software.

• Submit quarterly updates to HMRC.

• Complete a Final Declaration after the end of the tax year.

The aim is to make tax reporting more accurate while giving taxpayers a better view of their finances throughout the year.

Who Needs to Comply?

MTD for Income Tax is being introduced in stages based on your total qualifying income from self-employment and property.

• From April 2026: Individuals with qualifying income over £50,000.

• From April 2027: Individuals with qualifying income over £30,000.

• Expected from April 2028: Individuals with qualifying income over £20,000, subject to legislation.

What is qualifying income?

The MTD income threshold is based on your qualifying gross income from self-employment and property businesses before expenses are deducted. This includes UK property income and may also include overseas property or self-employment income if it forms part of your UK Income Tax reporting. Employment income, dividends and pension income do not count towards the threshold.

If you're unsure whether the rules apply to you, we're happy to help.

When Is My First MTD Submission Due?

If you join Making Tax Digital from 6 April 2026, your first quarterly reporting period covers: 6 April 2026 to 5 July 2026. Your first quarterly update must be submitted to HMRC by 7 August 2026, just over one month after the quarter end.

Other reporting period and submission deadlines are as follows:

• Quarter 2: Period covered: 6 July to 5 October. Submission deadline: 7 November

• Quarter 3: Period covered: 6 October to 5 January. Submission deadline: 7 February

• Quarter 4. Period covered: 6 January to 5 April. Submission deadline: 7 May

After your fourth quarterly update, you'll complete a Final Declaration, which replaces much of the current Self Assessment reporting process. This is normally due by 31 January following the end of the tax year.

Note - these are the standard quarterly periods. Some businesses may instead use calendar quarters (1 April to 30 June etc.) depending on their software and accounting period.

Do I need to pay tax quarterly now?

No, quarterly updates do not mean you'll pay tax every three months.

They simply keep HMRC updated on your income and expenses. Your tax payment dates remain unchanged.

What Should You Do Now?

If you think MTD may apply to you, we recommend taking these simple steps.

1. Check your income

Work out your annual self-employment and rental income to see whether you exceed the relevant threshold.

2. Move to digital records

If you're still relying on paper records or spreadsheets, now is the ideal time to move to digital bookkeeping.

3. Choose compatible software

You'll need HMRC-compatible software to comply with MTD. Choosing the right software now will make the transition much easier.

4. Get everything ready before your deadline. Don't wait until your first quarterly submission is due.

Setting everything up in advance gives you time to become familiar with the software and avoids unnecessary stress.

Do I Need Accounting Software?

Yes. Most taxpayers affected by MTD will need HMRC-compatible accounting software.

While spreadsheets can still be used in certain circumstances, they generally need to be linked to compatible software to meet HMRC's digital requirements.

Cloud accounting software also offers several additional benefits:

• Keep your records organised throughout the year.

• See your income and expenses in real time.

• Reduce paperwork.

• Estimate your tax position earlier.

• Make year-end tax reporting much simpler.

How Craigerne Accountancy Can Help

Making Tax Digital doesn't have to be complicated.

At Craigerne Accountancy, we can help you:

• Confirm whether MTD applies to you.

• Calculate whether you meet the income thresholds.

• Recommend suitable accounting software.

• Set up your digital bookkeeping.

• Prepare and submit your quarterly updates.

• Complete your Final Declaration.

• Provide ongoing support throughout the year.

Whether you're self-employed, a landlord, or both, we'll ensure you stay compliant while keeping the process as straightforward as possible.

Get in touch today to make your transition to Making Tax Digital simple and stress-free.