If your tax return tends to stay on the to-do list until winter, you are not alone.

The simplest answer to when to start your Self-assessment tax return is: as soon as you have the information you need. For 2025/26, HMRC accepts returns from 6 April 2026. The online filing and payment deadline is 31 January 2027, so starting early gives you time to check the figures and plan the payment.

Want help getting your return organised before January?

Our accountancy and tax services for individuals include Self-assessment support. We can help you prepare and submit the return in good time. Call us on 01322 250 001 or email info@adams-accountancy.co.uk.

When can you file a Self-assessment tax return?

For most people asking when to file a tax return in the UK, there is no need to wait until January. Once the tax year ends on 5 April, you can file from 6 April if your records are ready.

The 2025/26 return can be submitted online any time from 6 April 2026 up to 11:59pm on 31 January 2027. Paper returns normally have an earlier deadline of 31 October 2026.

Starting early does not mean paying early. If you file before January, the normal payment deadline is still 31 January. You can therefore know the bill in advance without bringing the due date forward.

Why is filing early usually easier?

Filing self-assessment early gives you more room to find missing records, query figures, and make sure relevant income and expenses have been considered.

It can also help with cash flow. HMRC says filing earlier lets you find out what you owe, budget for the bill, or explore a payment plan if paying on time may be difficult.

What is the Self-assessment deadline for 2025/26?

The 31 January Self-assessment deadline for the 2025/26 tax year is 11:59pm on 31 January 2027 for online returns. It is also normally the payment deadline for any balancing payment and a first payment on account where applicable.

If you are new to Self-assessment, you must normally tell HMRC by 5 October if you need to complete a return for the previous tax year and have not filed one before, or did not need to file for the preceding year.

If you register late, HMRC may give you a different filing deadline. Tax can still be due by 31 January, so do not assume late registration moves the payment date too.

What happens if you miss the January deadline?

A penalty could apply even if there is no tax to pay. Under the current rules, a late return can attract an initial £100 penalty. Further penalties can build if the return remains outstanding for three, six, and twelve months.

Late payment is separate from late filing. HMRC can also charge penalties and interest on unpaid tax. If you miss the deadline, file the return and deal with any unpaid tax promptly.

If you had a reasonable excuse for filing or paying late, HMRC allows appeals. The outcome depends on your circumstances.

What should you do if you are not ready to file?

Start by working out what is missing. That could be a P60, income and expense records, rental figures, dividends, or bank interest.

If you are unsure what belongs on the return, getting advice earlier gives you more time to resolve it. Our ICAEW chartered accountants and ATT-qualified team support individuals, sole traders, and subcontractors with personal tax and Self-assessment.

If you are looking for an accountant in Kent, you can contact our team to discuss what is outstanding.

Start when your records are ready, not when January arrives

Start once you have enough information to prepare the return properly. Filing earlier gives you time to check the numbers, understand the tax due, and plan for payment.

If the deadline is close or has passed, submit what is required and address any unpaid tax promptly.

Need a hand with your Self-assessment?

If you want your return checked, prepared, or submitted with professional support, call us on 01322 250 001 or email info@adams-accountancy.co.uk. We can help you understand what is needed and the next step for your situation.

Frequently asked questions

How early can I file my Self-assessment tax return?

You can normally file from 6 April after the tax year ends. For 2025/26, filing opened on 6 April 2026.

Does filing my tax return early mean I have to pay early?

No. Filing early does not normally change the 31 January payment deadline, although you can pay sooner if you prefer.

What is the online Self-assessment deadline for 2025/26?

The deadline is 11:59pm on 31 January 2027. Paper returns normally need to reach HMRC by 31 October 2026.

Is the £100 late filing penalty charged if I owe no tax?

Yes. The initial £100 penalty can apply even if there is no tax due or the tax was paid on time.

Can I appeal a Self-assessment late filing penalty?

Yes, if you have a reasonable excuse. HMRC considers appeals based on the circumstances of the delay.