Self-Assessment Deadlines and What You Need to Submit

If you are self-employed, a company director, or earn income outside of PAYE, completing a Self-Assessment tax return is one of your key responsibilities. It ensures that HM Revenue & Customs (HMRC) receives the correct information about your income and expenses so you can pay the right amount of tax. Missing a deadline or submitting inaccurate information can lead to penalties and unnecessary stress, so understanding the key dates and requirements is essential.

What is Self-Assessment?

Self-Assessment is HMRC’s system for collecting Income Tax from individuals and businesses whose income is not taxed automatically at source. It applies to self-employed individuals, business partners, landlords, company directors, and anyone who earns additional income from dividends, investments, or overseas sources. Each year, you must complete a tax return declaring your total income and allowable expenses for the previous tax year.

Important Self-Assessment Deadlines

There are several key dates throughout the Self-Assessment process and missing them can result in penalties. The deadlines apply to the tax year that runs from 6 April to 5 April.

• Registering for Self-Assessment: If this is your first time completing a tax return, you must register with HMRC by 5 October following the end of the tax year. For example, for the 2025/26 tax year (ending 5 April 2026), the registration deadline is 5 October 2026.
• Submitting a Paper Tax Return: If you prefer to file a paper tax return, HMRC must receive it by 31 October.
• Submitting an Online Tax Return: Most people now file online. The deadline for online submissions is 31 January following the end of the tax year. For example, for the 2025/26 tax year, you have until 31 January 2027 to file.
• Paying Your Tax Bill: Any tax due must also be paid by 31 January. Some taxpayers will also need to make a payment on account towards the following year’s bill by 31 July.

Submitting late or missing a payment deadline can result in penalties and interest charges, so it’s best to plan and complete your return well before the due date.

What You Need to Submit

When completing your Self-Assessment, you will need to include details of all income and allowable expenses for the tax year. The exact information required will depend on your circumstances, but typically includes:

• Employment income if you receive a salary and have a P60 or P45
• Self-employment income and expenses including invoices, receipts, and records of business costs
• Dividend income from shares or investments
• Rental income and associated property expenses for landlords
• Savings interest and other investment income
• Capital gains if you have sold assets such as property or shares
• Pension contributions and charitable donations that qualify for tax relief

It is vital to keep accurate records throughout the year, as HMRC may request evidence to support your figures. Good bookkeeping makes the Self-Assessment process much smoother and reduces the risk of mistakes.

How to Prepare Efficiently

Preparing for Self-Assessment doesn’t have to be stressful. Start by gathering all relevant financial documents early, including bank statements, receipts, invoices, and payslips. Using accounting software or working with an accountant can make the process far more efficient and reduce the chance of errors.

If you are self-employed, ensure you claim all allowable business expenses such as office supplies, travel, and professional fees. This helps reduce your taxable income and ensures you are not paying more tax than necessary.

It is also wise to set aside funds for your tax bill throughout the year rather than waiting until the deadline. This helps avoid cash flow problems and ensures you can pay your tax on time.

Final Thoughts

Understanding Self-Assessment deadlines and what needs to be submitted is essential for staying compliant and maintaining control over your finances. By keeping organised records, preparing early, and taking professional advice when needed, you can avoid penalties and ensure your tax return is accurate.

Working with an accountant provides peace of mind, as they can manage your submission, check for available allowances, and help you plan for future tax years. Staying ahead of deadlines is not only good practice but a crucial step towards efficient financial management and business success.

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