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January is the point in the year when Self-Assessment moves from the background to the top of the to-do list.
For some people, it is a familiar annual process. For others, it is the first time they realise their circumstances now require a tax return — often when the deadline is already close. A change in income, a new role, additional earnings, or moving away from standard PAYE arrangements can all bring Self-Assessment into focus.
Understanding how Self-Assessment works, and what HMRC expects, makes the process far more manageable and helps avoid unnecessary pressure at the start of the year.
What Is Self-Assessment?
Self-Assessment is an annual tax return covering income earned between 6 April and 5 April.
Rather than HMRC calculating your tax automatically, you are required to report your income and confirm that the information submitted is complete and accurate. Based on what is declared, HMRC then calculates how much tax is due.
As part of the return, you report:
- what income you received
- where that income came from
- any allowable deductions or reliefs
The responsibility for accuracy always sits with the taxpayer, even when professional support is used. The declaration is made in your own name, which is why clarity and correctness matter.
Who Needs to Complete a Self-Assessment?
You may need to file a Self-Assessment tax return if you:
- are self-employed or operate as a sole trader
- are a company director
- receive rental income
- earn income from savings, dividends or investments
- have income from abroad
- earn over £100,000
- have more than one source of income
Not everyone in these categories will automatically be required to file, but many are. In practice, company directors and business owners are among those most affected, particularly where income is received outside standard PAYE or where circumstances change during the year.
If you are unsure whether Self-Assessment applies to you, it is best to check rather than assume. Leaving it until January often limits your options and creates unnecessary pressure.
Key Dates to Be Aware Of
There are two deadlines that matter most:
5 October
This is the deadline to register for Self-Assessment if you have never filed before. Missing this date does not remove the obligation to file, but it can create complications later.
31 January
This is the deadline to submit your online tax return and pay any tax due for the previous tax year.
Missing these deadlines can result in automatic penalties, even if no tax is ultimately owed. Interest may also be charged on unpaid amounts.
What Information Do You Need?
To complete a Self-Assessment, you will usually need to gather information covering the entire tax year.
This typically includes:
- details of all income received during the year
- records of business expenses, where applicable
- bank and building society interest statements
- dividend statements
- rental income and associated costs
- pension contributions and Gift Aid donations
Keeping clear and organised records throughout the year makes the process significantly simpler. It also reduces the risk of errors or omissions, which can lead to HMRC queries later on.
How Is the Tax Paid?
Once your return has been submitted, HMRC will confirm:
- the amount of tax due
- whether payments on account apply
- the deadline by which payment must be made
Payment is typically made online, most commonly by bank transfer, direct debit or debit card.
Payments on account often come as a surprise, particularly for first-time filers or those whose income has increased. Understanding how they work is an important part of managing cash flow.
What Happens If You File or Pay Late?
If you miss the 31 January deadline:
- an automatic penalty applies
- interest is charged on any unpaid tax
- further penalties may follow if delays continue
If you are unable to pay the full amount immediately, it may be possible to agree a Time to Pay arrangement with HMRC. This must be requested and approved — it is not applied automatically.
Addressing issues early generally gives you more flexibility than waiting until penalties begin to accumulate.
When Does Self-Assessment Become More Complex?
Self-Assessment is usually straightforward when income is simple and consistent.
It often becomes more complex when:
- income comes from multiple sources
- business and personal income overlap
- dividends or director remuneration are involved
- property or overseas income forms part of the picture
- circumstances change during the year
In these situations, accuracy matters more than speed. A return that reflects the full financial picture is far more valuable than one submitted quickly without proper consideration.
A Practical, Long-Term Approach
At J. Dauman & Co., we work with UK-based business owners and directors who want their Self-Assessment to reflect their actual position — not just meet a deadline.
For many clients, the value lies not only in filing the return, but in understanding how different income streams fit together and how decisions made during the year affect the outcome.
If your circumstances have changed, or your income is no longer straightforward, addressing this early allows for clearer decisions and a far smoother January.
To discuss your Self-Assessment speak to our team