Self-Assessment Deadline 2026: When to get help with your tax return

What is self-assessment?

Self-assessment is the system used by HM Revenue & Customs (HMRC) to collect Income Tax from individuals and businesses whose tax isn’t fully handled through PAYE. It’s most commonly used by self-employed people, landlords, and company directors who receive income in different ways throughout the year.

Rather than HMRC calculating everything automatically, self-assessment places the responsibility on you to manage your tax affairs. This means you must:

• Report all relevant income accurately
• Claim allowable expenses correctly
• Submit your return and pay any tax owed on time

The tax year runs from 6^th April to 5^th April, and your self-assessment return covers all income earned during that period, even if the money is paid later.

For independent businesses and individuals, this typically includes trading income, rental income, dividends, and other taxable income that isn’t taxed at source. Understanding what needs to be included and how it should be reported, is a key part of avoiding mistakes later on.

Key self-assessment deadlines for 2026

Knowing your deadlines is critical and one of the most common areas people fall behind.

For the 2024/25 Tax Year (6 April 2024 – 5 April 2025)

• Register for self-assessment: by 5^th October 2025 (passed)
• Paper return deadline: 31^st October 2025 (passed)
• Online return & tax payment deadline: 31^st January 2026

For the 2025/26 Tax Year (6 April 2025 – 5 April 2026)

For the 2026 tax year, income you make this year:

• Register for self-assessment: by 5^th October 2026
• Online return: by 31^st January 2027
• Tax payment due: 31^st January 2028

Miss the January deadline and you’ll face:

• An automatic £100 penalty
• Daily penalties after 3 months
• Interest on unpaid tax

Even if you owe no tax, penalties still apply.

How to register for self-assessment

If this is your first time, you must register with HMRC before you can file. Before you can start, you need a Unique Taxpayer Reference (UTR).

When to register

You’ll need to register by 5^th October following the end of the tax year you need to report. For example, for the tax year 2025-2026, you’ll need to register by 5^th October 2026.

HMRC will send you a Unique Taxpayer Reference (UTR) by post, this can take time, so don’t leave it until the last minute. You can also download the HMRC app, which provides easy access to check your details and obtain further information.

How to file your self-assessment return

Online filing

Most independent businesses file their self-assessment tax return online, either directly through HMRC or using approved accounting software. Online filing is usually the simplest option, with automatic calculations, built-in checks, and a later deadline than paper returns.

Before you can file, you’ll need a Unique Taxpayer Reference (UTR) from HMRC and a Government Gateway ID to access their online services.

If this is your first time filing, it’s worth allowing extra time for registration and setup, as these steps can’t always be completed instantly.

Paper Filing

From 6^th April 2026 (the next tax year) paper filing will no longer be possible. Everyone is expected to adopt the Making Tax Digital process, unless given an exemption directly from HMRC.

Find more about the Making Tax Digital system and deadline.

What information you’ll need to file

Preparation is where many people struggle and where mistakes creep in.

You’ll typically need:

• Total business income
• Rental income (if applicable)
• Allowable expenses
• PAYE income (if you also have a job)
• Dividend income
• Student loan details
• Pension contributions

Good records make filing easier, reduce stress, and help avoid overpaying tax.

Who does self-assessment apply to?

Self-assessment applies to more people than many expect, plus you may have different criteria depending on your how you operate.

How your business is structured plays a big role in which taxes you pay, how you report income, and what deadlines apply. Below is a simple overview of how tax responsibilities typically differ across common business types, helping you quickly see what applies to your situation and what you may need to keep in mind as your business grows.

Below is a practical overview of the most common business types and how self-assessment typically applies to each.

Self-employed or a Sole trader

This includes sole traders, freelancers, contractors, and consultants.

If you’re self-employed, you’ll usually:

• Pay Income Tax via self-assessment
• Pay National Insurance contributions
• Have a simpler structure, but personal liability for tax and debts

Freelancers and contractors often have additional complexity, such as:

• Multiple income streams
• Possible IR35 considerations when contracting

Anyone earning more than £1,000 from self-employment or a side hustle typically needs to register.

Small limited company director

If you’re a director of a limited company, your tax responsibilities are different, even if the company is small or not actively trading.

You may need to file self-assessment if you:

• Take a salary and/or dividends
• Receive benefits or other untaxed income

Limited companies themselves:

• Pay Corporation Tax
• Are a separate legal entity
• Have additional reporting and filing obligations

This distinction often catches new directors out, especially when mixing personal and company income.

Landlords

Self-Assessment usually applies if you earn income from property, including:

• Residential or commercial property
• UK or overseas rental income
• Jointly owned property (each owner files separately)

Property income has its own rules and allowable expenses, which can make returns more complex than expected.

Partnerships & other income sources

You may also need to complete a Self-Assessment tax return if you earn income alongside your main job or business, or if your income doesn’t fit neatly into a single category.

This commonly includes:

• Shared profits through a partnership or joint venture
• Side-hustle or second income, such as online selling, freelance work, or gig economy platforms
• Other untaxed income, including foreign income, capital gains, or multiple income streams

Side-hustle income is a frequent source of confusion, particularly for people who already pay tax through PAYE. Even if your main job is taxed automatically, additional income over £1,000 in a tax year usually needs to be declared through Self-Assessment.

Where income comes from multiple sources, reporting becomes more detailed, and it’s easier to overlook something. In these situations, checking early, or seeking advice, can help ensure everything is declared correctly and reduce the risk of penalties later.

How to pay your self-assessment tax

Understanding when and how income tax is paid can make a big difference to cash flow, especially for sole traders and self-employed business owners. Rather than paying tax automatically through payroll, income tax is usually settled after you’ve submitted your Self-Assessment return, which can feel unfamiliar if you’re new to running a business.

This section breaks down the main types of income tax payments you might be asked to make, what they mean in practice, and why they sometimes come as a surprise.

Balancing payments

A balancing payment is the amount you owe for the previous tax year once your Self-Assessment return has been submitted and HMRC has calculated your final bill.

This payment is usually due by 31^st January and reflects any tax that hasn’t already been paid through PAYE or payments on account.

Payments on account

If your income tax bill is over £1,000, HMRC may ask you to make payments on account towards the next tax year’s bill. These are split into two instalments:

• 50% by 31^st January
• 50% by 31^st July

These advance payments are based on your previous year’s tax bill and are designed to spread the cost, but they can be unexpected, particularly in your first year of trading or after a profitable year.

Payment methods include:

• Bank transfer
• Debit card
• Direct Debit
• HMRC app

Late payments

If tax payments are made late, HMRC may apply:

• Automatic penalties
• Daily interest charges
• Enforcement action if the debt is ignored

If you’re struggling to pay on time, contacting HMRC early can sometimes help, as support options may be available.

Read more on what happens if you miss the tax return deadline.

Common self-assessment mistakes

Most self-assessment mistakes aren’t caused by carelessness, they happen because deadlines are easy to miss, tax rules aren’t always clear, and many people are juggling this alongside running a business. Accountants see the same issues arise year after year, particularly among small businesses and first-time filers who are managing the process themselves.

The most common problems include:

• Missing key deadlines, including registration, filing, or payment dates
• Misunderstanding payments on account, leading to unexpectedly high tax bills
• Errors in reporting, such as under-declaring income or claiming expenses incorrectly

While these mistakes might seem minor at first, their impact can be significant. Even small errors can trigger:

• Automatic penalties and interest charges
• HMRC enquiries or audits, which take time and energy to resolve
• Cash-flow issues, especially if unexpected tax bills arrive at short notice

Spotting risks early, keeping clear records, and asking for help when something doesn’t make sense can prevent most of these issues before they escalate.

How to get help

Knowing when and how to get help can make a significant difference to a smooth process. Tax rules aren’t always intuitive, and as we’ve seen from common errors, small misunderstandings can lead to costly errors, missed reliefs, or unexpected bills.

Getting support is strongly recommended if you’re facing any uncertainty, particularly if:

• You’re filing a self-assessment return for the first time, or your circumstances have recently changed
• You’re unsure what counts as an allowable expense or how to report different types of income
• Your tax bill is higher than expected, payments on account don’t make sense, or you’ve missed a deadline

Even a short conversation with an accountant or tax adviser can clarify your position, highlight potential savings, and help you avoid problems that can otherwise linger for years.

Ways to get support

There are several ways to access help, depending on how much guidance you need:

• Official HMRC guidance and helplines, which can help explain deadlines, forms, and basic requirements
• Accounting software with built-in support, often useful for straightforward returns and ongoing record-keeping
• Professional accountants, bookkeepers, or tax advisers, particularly valuable for landlords, limited company directors, or anyone with multiple income streams

The key is choosing support that matches your situation. For some, a tutorial or software prompt is enough. For others, professional advice can quickly pay for itself by reducing risk and ensuring everything is done correctly.

Discover more on when to hire an accountant.

Plan early, avoid stress

While we’ve highlighted where things often go wrong, it’s worth remembering that millions of people successfully complete their self-assessment each year. With early planning, clear records, and seeking support when needed, most mistakes are completely avoidable.

If you’re self-employed, running a small, limited company, or earning rental income, taking time now to understand your obligations, prepare for key deadlines, and decide whether you need help can make the process far less stressful — and your future self (and bank balance) will thank you.

*Disclaimer – This blog has been created as general information and should not be taken as advice. Make sure you have the correct level of insurance for your requirements and always review policy documentation. Information is factually accurate at the time of publishing but may have become out of date.