Self Assessment tax can be confusing when you have several sources of income. You may need to report business profits, rent, dividends, savings interest or gains from selling assets.

Every figure must relate to the correct tax year. You must also claim expenses under the right tax rules. A missing income source or unsupported expense may result in an incorrect bill.

SAS Accountants helps sole traders, landlords, company directors and other individuals prepare their returns. The service covers registration, record checks, tax calculations and online submission to HMRC.

What Is Self Assessment Tax?

Self Assessment is HMRC’s system for collecting tax that has not already been deducted from income. Employees often pay Income Tax through PAYE. However, PAYE may not collect all the tax due when someone has other income.

A Self Assessment return reports income, gains, expenses and relevant tax reliefs. HMRC then uses these details to determine the final liability.

The UK tax year runs from 6 April to 5 April. A return must include information for the correct period. Using documents from the wrong year may produce an inaccurate calculation.

SAS Accountants can review each income source and place the figures in the right sections of the return.

Who May Need to Submit a Tax Return?

Self-employed people may need to register when their gross trading income goes above the trading allowance. Business partners also report their share of partnership income through their own returns.

Landlords may need to file when they receive taxable rental income. A return may also be required for dividends, savings income, foreign income or gains from selling chargeable assets.

Some taxpayers need to file because of the High Income Child Benefit Charge. Others receive a notice from HMRC requiring them to submit a return.

If HMRC has issued a notice to file, you should not ignore it. You generally need to submit the return unless HMRC confirms that it has withdrawn the notice.

SAS Accountants can examine your circumstances and help determine which information must be reported.

Registering with HMRC

You must register before you can submit your first return. HMRC will normally issue a Unique Taxpayer Reference, known as a UTR.

For the 2025/26 tax year, a new taxpayer who needs to file should have told HMRC by 5 October 2026. This also applies to someone who registered in the past but did not need to file for 2024/25.

Missing the registration date does not remove the duty to report. You should register as soon as possible and prepare the return without further delay.

SAS Accountants can help with registration and explain what information HMRC may request.

Self Assessment Deadlines for 2025/26

The 2025/26 tax year started on 6 April 2025 and ended on 5 April 2026.

Paper returns are generally due by 31 October 2026. Online returns and outstanding tax payments are generally due by 11:59 pm on 31 January 2027.

HMRC confirms that the payment deadline for the 2025/26 return is 31 January 2027. A second payment date of 31 July may apply when payments on account are due.

Submitting early does not bring the normal payment date forward. It allows you to learn the amount sooner and plan how it will be paid.

What Records Do You Need?

The documents required will depend on the income reported. A sole trader may need sales records, bank statements, invoices and expense receipts.

An employee may need a P60, P45 or P11D. A landlord may need rent statements, mortgage information, agent statements and invoices for property costs.

Investors may need dividend vouchers and interest statements. Anyone who sold an asset may need documents showing its purchase price, disposal proceeds and related costs.

You should also keep details of pension contributions and eligible charitable donations. These payments may affect the final calculation in some cases.

SAS Accountants can provide a record checklist based on your income and financial activities.

Reporting Self-Employment Income

A sole trader must report business income and allowable costs. The difference between the two usually forms the starting point for taxable profit.

Business income includes payments received for goods or services. It can also include amounts received through digital platforms, card processors or online marketplaces.

The business should keep records that support the figures. Bank deposits alone may not explain the source of each payment. Clear invoices and sales records make the return easier to prepare.

SAS Accountants can organise the records and prepare the sole trader accounts used for the return.

Claiming Business Expenses

Allowable expenses reduce taxable business profit. The exact costs depend on the type of work carried out.

Common claims may include office costs, accountancy fees, advertising, business insurance and certain travel expenses. A person who works from home may also be able to claim part of relevant household costs.

Personal spending cannot be claimed as a business cost. When an expense has both personal and business use, only the business element may qualify.

Buying equipment can also require different treatment from paying a routine expense. Capital allowances or other rules may apply.

SAS Accountants can examine the purpose of each cost and apply the correct treatment.

Self Assessment Tax for Landlords

Landlords must report taxable property income. The calculation normally begins with rent and other amounts received from tenants.

Allowable property costs may include letting agent fees, insurance and qualifying repairs. However, an improvement may be treated differently from a repair.

Finance costs for residential property also have specific tax rules. They are not always deducted in the same way as other expenses.

Landlords with several properties need records for each one. This helps track income, costs and any periods when a property was empty.

SAS Accountants can prepare rental accounts and include the correct figures in the property section of the return.

Reporting Capital Gains

Selling property, shares or other chargeable assets may create Capital Gains Tax. The calculation is not based only on the amount received.

You may need the original purchase cost, legal fees, selling costs and qualifying improvement expenditure. Previous capital losses and available reliefs may also affect the result.

Some UK property disposals have separate reporting and payment requirements. They may still need to appear in the annual return.

SAS Accountants can review disposal documents and calculate the gain before the return is completed.

Understanding Payments on Account

Payments on account are advance payments towards a future Self Assessment liability. They often apply when the tax due is above the relevant limit and too little has been collected at source.

There are normally two instalments. The first is due on 31 January. The second is due on 31 July. Each payment is usually half of the previous year’s qualifying liability.

This means the amount due in January can include a balancing payment and the first advance payment for the next year.

If income is expected to fall, you may be able to reduce the payments. The estimate should be reasonable. Reducing them too far may lead to interest when the final bill is calculated.

SAS Accountants can explain how each part of the bill has arisen and whether a reduction should be considered.

What Happens If You File Late?

Missing the filing date can lead to penalties. Interest and further charges may also apply when tax remains unpaid.

A late registration can create a failure-to-notify penalty when tax has not been paid by the payment date. The amount can depend on the unpaid tax and the circumstances behind the delay.

If you have missed a deadline, you should still file as soon as possible. Waiting longer may increase the amount owed.

A reasonable excuse may support an appeal in some situations. Evidence should be kept to explain what happened and when the issue was resolved.

SAS Accountants can help bring overdue returns up to date and review HMRC notices.

Making Tax Digital for Income Tax

Making Tax Digital for Income Tax changed the reporting process for some sole traders and landlords from 6 April 2026.

It applies from 2026/27 to qualifying people whose gross self-employment and property income exceeded £50,000 in 2024/25. A £30,000 threshold applies from April 2027, based on 2025/26 qualifying income. The threshold is due to fall to £20,000 from April 2028.

Those within the rules must keep digital records and use compatible software. They also need to provide quarterly updates and complete the required year-end process.

SAS Accountants can check whether the rules apply and help establish a suitable record-keeping process.

Common Self Assessment Errors

One common error is failing to declare all income. Taxpayers sometimes assume that information held by HMRC does not need to appear on the return.

Another problem is claiming personal costs as business expenses. People may also use documents from the wrong tax year or forget to report rental income and capital gains.

Incorrect bank details can delay a repayment. An old address may also cause HMRC correspondence to be missed.

Preparing the return early gives more time to identify these issues. It also allows the figures to be checked before submission.

Why Use SAS Accountants?

Tax returns can become difficult when income comes from several sources. The work may involve business accounts, property figures, investments and capital gains.

SAS Accountants reviews the wider tax position rather than entering figures without checking their source. The team can help with registration, accounting records, expense claims and tax calculations.

Clients can review the return and ask questions before it is filed. They will also receive an explanation of the tax bill and payment dates.

The service is available to sole traders, landlords, directors and individuals across the UK.

Contact SAS Accountants

Do not wait until the January deadline to begin collecting information. Early preparation gives you time to find missing records and plan for the bill.

SAS Accountants can prepare your Self Assessment tax return and submit it to HMRC. The team can also help with overdue returns, payments on account and Making Tax Digital.

Visit SAS Accountants or call 0330 133 0278 to discuss your tax return.

Frequently Asked Questions

1. Can SAS Accountants submit my return to HMRC?

Yes. SAS Accountants can prepare and submit the return after receiving the required records and agent authorisation. You will have an opportunity to review the figures before filing.

2. Do I need to file if no tax is due?

You may still need to file if HMRC has issued a notice requiring a return. Contact HMRC or seek advice if you believe the notice should be withdrawn.

3. Can I claim expenses without receipts?

You should keep evidence supporting expense claims. Other records may sometimes help when a receipt is missing, but each cost must still be genuine and related to the business.

4. Why is my January bill larger than expected?

The amount may include the remaining tax for the completed year and the first payment on account for the next year. Your calculation should show these amounts separately.

5. Can I correct a return after filing it?

A return can normally be amended within the permitted time limit. The method depends on how the original return was filed and when the error was found.