28 August 2026 – written by Steffen Kemmerzehl – Friendly Assist Accountancy – The Accounting Hub
Summer is nearly over, children are going back to school and for many businesses September means getting back into a more normal routine. January still feels a long way away, but if you need to complete a Self Assessment tax return for 2025/26, this is actually a very good time to deal with it.
The tax year ended on 5 April 2026 and the online filing deadline is 31 January 2027. That does not mean there is any benefit in waiting until January. Filing earlier can give you more time to budget, deal with missing information and, in some circumstances, make use of options that may no longer be available if you leave the return until the last minute.
Find Out What You Actually Owe
For many people, the biggest advantage of preparing a tax return now is certainty. A sole trader may know roughly how much profit the business made but that does not necessarily tell them what will actually need to be paid in January.
For example, someone whose tax liability is high enough to bring them into payments on account could have a balancing payment for 2025/26 as well as the first payment on account towards 2026/27 due on 31 January. This can make the January payment considerably larger than expected.
If the calculation is completed in September, there are around four months to prepare for that payment. If it is completed on 28 January, there are only a few days.
Filing early does not normally mean paying early. The normal payment deadline still applies, so getting the return completed can give you certainty without requiring you to hand the money to HMRC months ahead of time.
There Is an Earlier Deadline That Some People Should Know About
The 31 January deadline gets most of the attention, but there is another date which can matter.
If you owe less than £3,000 through Self Assessment and already pay tax through PAYE, HMRC may be able to collect the Self Assessment liability through your PAYE tax code, provided its other conditions are satisfied.
For example, somebody may be employed but also receive £8,000 of rental income or have a small self-employed business alongside their job. Their additional tax bill might be £1,800. Instead of paying the entire £1,800 directly in January, it may be possible for HMRC to adjust their tax code and collect the amount through their salary.
However, if you want HMRC to consider collecting an eligible bill through PAYE, an online return generally needs to be submitted by 30 December, not 31 January.
It is a small rule, but potentially a useful one. Waiting until the January deadline can mean losing a payment option that might otherwise have been available.
Payments on Account May Not Match What Your Business Is Doing Now
Another reason for dealing with the return earlier is that payments on account are based on previous tax liabilities, while businesses can change considerably from one year to another.
Imagine a self-employed person had an unusually strong 2025/26 but their income has fallen substantially during 2026/27. Their payments on account may therefore be based on a level of profit they no longer expect to achieve.
It may be possible to apply to reduce payments on account where the expected liability is genuinely lower. This needs to be done carefully because reducing them too far can result in interest if the eventual liability is higher.
Preparing the figures earlier gives you time to look at whether the payments make sense rather than simply discovering the amount shortly before it becomes payable.
Moving Abroad During the Tax Year Can Change More Than You Think
Some of the biggest differences arise where circumstances have changed during the year.
Suppose somebody lived and worked in Newcastle until September 2025 and then moved overseas to take up full-time employment. They may assume that because they spent part of the year in Britain they are simply UK resident for the whole tax year, or alternatively that leaving the UK means everything earned afterwards is automatically outside UK tax.
Neither assumption should be made without checking the facts.
The UK’s Statutory Residence Test determines residence and there are eight different split-year cases which can potentially apply when somebody arrives in or leaves the UK. Where the relevant conditions are met, the tax year can be divided into a UK part and an overseas part.
That can make a substantial difference to the treatment of income received after somebody leaves the UK or before they arrive here.
It is also why questions such as when you left, where you lived afterwards, how many days you spent in the UK and when overseas employment started can matter. These are much easier to establish in September than during a rushed conversation a few days before the filing deadline.
An Overseas Secondment Can Make a PAYE Return Less Straightforward
PAYE is another area where people understandably assume that because their employer deducted tax, there cannot be much else to consider.
Usually that is perfectly reasonable. But international employment can be different.
Consider an employee of a UK company who spends much of the year working on an overseas secondment, or somebody who returns to Britain after working abroad. Their employer may have operated PAYE based on the information available to it, and an employee working overseas may in some circumstances have had an NT, or “no tax”, code.
That tax code is part of the PAYE collection system. It does not by itself determine the employee’s final residence position or establish the final amount of UK tax due.
So if somebody tells us, “I was PAYE, but I spent eight months working in Germany”, that is information worth looking at rather than simply copying the figures from the P60 into the return.
The same principle applies to people who worked in several countries, returned to the UK part way through the year or had foreign income alongside UK employment.
You Could Be Due a Refund Rather Than a Bill
There is also a tendency to associate Self Assessment with paying HMRC, but that is not always the outcome. Tax may already have been deducted through PAYE or another source, while payments on account made during the year may turn out to have been higher than the final liability.
Completing the return establishes the actual position. If too much tax has been paid, a repayment may be due, although HMRC can use repayments against certain other amounts owed.
If you are due money back, there is little advantage in waiting until January simply to find that out.
Early Filing Gives More Time to Find the Things People Forget
The tax calculation itself is often not the part that causes delays. It is finding the information behind it.
A sole trader might discover that several months of bank statements are missing. A landlord may have forgotten about an insurance payment or repairs carried out early in the tax year. Someone with investments might need to find interest or dividend figures, while a CIS subcontractor may need to reconcile deductions shown on statements against payments actually received.
More unusual circumstances can take longer still. Overseas income may require foreign tax information, a move abroad may require travel dates, and an employment issue may mean checking P60s, payslips and tax codes.
Starting now means there is time to establish what actually happened rather than making assumptions because the deadline is approaching.
January Is a Deadline, Not a Target
There is nothing wrong with filing a tax return in January. But there is also no particular advantage in deliberately waiting for January when the information is already available.
Getting the return prepared earlier can tell you what you owe, give you time to budget, allow payments on account to be reviewed and identify less obvious issues such as PAYE coding, overseas work or split-year treatment while there is still time to investigate them properly.
Sometimes an early tax return simply gets an administrative job off your desk. Sometimes it identifies something that makes a meaningful difference.
Summer Is Over. Your Tax Return Can Be Too.
At Friendly Assist Accountancy, we prepare Self Assessment tax returns for sole traders, landlords and individuals, including cases where the position is not completely straightforward.
If you have overseas income, have moved into or out of the UK, worked abroad, had an unusual PAYE position or simply are not sure what needs to go on your return, it is worth raising this when the return is prepared rather than assuming it does not matter.
Self Assessment tax returns start from £119. More complex and international cases are quoted separately.
If your 2025/26 records are ready, or you are unsure whether you have everything you need, get in touch with Friendly Assist Accountancy and get your tax return sorted before winter.
Steffen Kemmerzehl
I am a qualified AAT accountant in Newcastle upon Tyne.
Please get in touch if you’re interested in arranging an appointment.