Self Assessment 2025/26: What You Need to File

If you’re required to complete a Self Assessment tax return, 31 January 2026 is a deadline you can’t afford to miss. This is the date by which your 2025/26 tax return must be filed and any tax owed paid to HMRC.

Whether you’re self-employed, a landlord, or have additional income outside PAYE, this guide explains exactly what you need to file, what information you’ll need, and what happens if you miss the deadline.

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Who Needs to File a Self Assessment for 2025/26?

You’ll usually need to submit a tax return if, during the 2024/25 tax year (6 April 2025 to 5 April 2026), you:

• Were self-employed or a sole trader
  
• Were a company director
  
• Earned rental income from property
  
• Had untaxed income (side hustles, freelance work, overseas income)
  
• Earned over £100,000
  
• Received dividends or significant savings interest
  
• Needed to pay Capital Gains Tax
  
• Claimed Child Benefit with income over the threshold
  

Not sure if you need to file? Many people submit returns unnecessarily, getting advice can save time and stress.

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What You Must Submit by 31 January 2026

By the deadline, you must:

1. File Your Self Assessment Tax Return

This includes:

• Your personal details
  
• All income for the 2025/26 tax year
  
• Any allowable expenses
  
• Relevant tax reliefs or allowances
  

Most people file online, though paper returns had an earlier deadline (31 October 2025).

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2. Pay Any Tax You Owe

You may need to pay:

• Income Tax
  
• Class 2 and Class 4 National Insurance
  
• Capital Gains Tax (if applicable)
  
• Student loan repayments
  

If your tax bill is over £1,000, you may also need to make a payment on account towards your 2025/26 tax bill.

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Information You’ll Need to Prepare Your Return

Gathering everything in advance makes filing much easier. You may need:

Income Records

• Self-employment income and invoices
  
• P60 or P45 (if employed)
  
• Dividend vouchers
  
• Bank interest statements
  
• Rental income records
  
• Foreign income details
  

Expense Records (if self-employed or a landlord)

• Office costs and software
  
• Travel and mileage
  
• Professional fees
  
• Phone and internet use
  
• Repairs and maintenance (for rental properties)
  

Other Information

• Pension contributions
  
• Gift Aid donations
  
• Student loan balance
  
• Capital gains calculations
  

Good record-keeping is one of the easiest ways to reduce errors and avoid HMRC queries.

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What Happens If You Miss the Deadline?

Missing 31 January 2026 can be costly:

• £100 automatic late filing penalty
  
• Daily penalties after 3 months
  
• Interest charged on unpaid tax
  
• Additional penalties for long delays
  

Even if you can’t pay the tax, it’s still important to file the return on time, payment plans may be available, but penalties for late filing are not easily removed.

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Should You Use an Accountant?

Many people underestimate how complex Self Assessment can be. An accountant can:

• Ensure you claim all allowable expenses
  
• Reduce the risk of errors or penalties
  
• Advise on tax planning for future years
  
• Deal with HMRC on your behalf
  

In many cases, the tax savings alone can outweigh the cost of professional help.

January is the busiest time of year for accountants and the most stressful for taxpayers. If you’d like help with your 2024/25 Self Assessment, or you’re unsure whether you need to file at all,  or need advice, get in touch with us.