31 January has a habit of arriving quicker than expected.

If you need to complete a Self Assessment tax return for the 2025/26 tax year, the deadline for submitting your online return and paying the tax you owe is generally 31 January 2027.

But that doesn’t mean 31 January should be the date you start thinking about it.

At Barrons, receiving your information early gives our team time to prepare your return properly, raise any queries and, importantly, tell you how much tax you need to pay well before the deadline.

What information does your accountant need for Self Assessment?

Exactly what we’ll need depends on your individual circumstances, but it may include:

  • Employment income, including your P60, P45 and P11D where applicable
  • Self-employment income and business expenses
  • Rental and other property income and expenses
  • Dividend income
  • Bank and building society interest
  • Pension income and pension contributions
  • Details of investments sold during the year
  • Capital gains information
  • Details of other taxable income
  • Information relating to relevant tax reliefs or allowances
  • Student loan information, where applicable
  • Details of any other significant changes to your financial circumstances

If you’re unsure whether something is relevant, send it to us or ask. We’d rather have too much information than discover something important at the last minute.

Why does Barrons ask for your information early?

Sending your records early isn’t simply about making your accountant happy — although we certainly won’t complain.

It gives us more time to make sure your return is accurate and complete, identify missing information and discuss anything unusual with you.

More importantly, completing your tax return earlier means you can know your tax liability sooner.

The payment deadline doesn’t become earlier simply because your return has been prepared early. Instead, you have more time to plan your cash flow and make sure the funds are available when payment is due.

What happens if I miss the 31 January deadline?

Submitting a Self Assessment tax return late can result in an initial £100 late filing penalty. Further penalties can apply if the return remains outstanding.

Late payment can also result in interest and additional penalties.

In other words, leaving everything until 31 January can turn an already busy month into a considerably more expensive one.

Don’t forget payments on account

Your January payment may include more than the balancing payment for the previous tax year.

Depending on your circumstances, you may also be required to make a payment on account towards your next tax bill.

This can sometimes catch taxpayers by surprise, particularly those completing Self Assessment for the first time.

Knowing the figures early means knowing what is coming.

Do I need to wait until January to submit my tax return?

No.

A 2025/26 Self Assessment tax return can be submitted well before January 2027.

And while we appreciate that tax returns aren’t necessarily at the top of everyone’s summer reading list, there are very few advantages to deliberately leaving yours until the last minute.

Let Barrons take care of your Self Assessment

Whether you’ve been completing Self Assessment for years or this is your first tax return, our team can help make the process straightforward.

Send us your information early, we’ll take care of the numbers, and you can enjoy January without a last-minute search for that one missing document.

Already a Barrons client? Send your Self Assessment information to your usual Barrons contact as soon as it’s available.

Need help with your Self Assessment? Speak to the Barrons Personal Tax team to find out how we can help.

This article provides general information only. Your tax position will depend on your individual circumstances and professional advice should be sought where appropriate.