Don’t panic! The ultimate Self Assessment guide (updated for 2026)

If you’re self-employed and reading this article, it’s likely that you’ve put off completing your Self Assessment tax return.

Don’t worry, there’s still time. We’ve shared resources and information you’ll need to make the process as straightforward as possible.

What’s the deadline for completing my Self Assessment?

Self Assessment is the system HMRC uses to collect your National Insurance Contributions (NICs) and income tax for the previous financial year.

The Self Assessment deadline for the 2024-2025 tax year is 31 January 2026. You also need to pay your tax bill by this date.

In the UK, the financial year starts on 6 April and ends on 5 April. That means the return that’s due on 31 January 2026 covers 6 April 2024 to 5 April 2025.

What are the penalties for late completion?

You will get a penalty for sending your return or paying your bill late.

This can include an initial £100 penalty and additional fines after three months for filing late, and a percentage charge for late payment.

The Gov.uk guidelines explain how these fees are applied.

Speak to HMRC if you’re worried about being able to complete your tax return. The phone lines are busy at this time of year, but they are helpful and you may be able to negotiate an extension.

Who needs to complete the Self Assessment?

If you're registered as self-employed, you'll be responsible for paying your own taxes.

You must send a tax return if, in the 2024-2025 tax year, you were:

• self-employed as a sole trader and earned more than £1,000 (before taking off anything you can claim tax relief on)

• a partner in a business partnership

You may need to send a Self Assessment tax return if you have any other untaxed income from the 2024-2025 tax year, such as:

• money from renting out a property

• tips and commission

• income from savings, investments and dividends

• foreign income

You can read the government guidelines on who needs to complete a return and use their tool to check if you need to complete a Self Assessment tax return.

How can I file my Self Assessment tax return?

You can file your tax return online – 97% of people choose to do it this way, according to the Gov.uk website.

Paper tax returns were due by 31 October 2025 for the 2024-2025 tax year.

What information will I need to fill in a Self Assessment?

If you've never filled in a Self Assessment tax return before, it can seem complex. However, once you understand the process, it's relatively simple, as long as you have the relevant information to hand:

• your 10-digit unique taxpayer reference (UTR) number

• your Government Gateway User ID

• your National Insurance number

• details of your untaxed income from the tax year, including income from self-employment, dividends and interest on shares

• records of any expenses relating to your self-employment

• details of any contributions to charity or pensions which might be eligible for tax relief

• a P60 or other documents showing how much income you've received and already paid tax on

• a P11D if you’ve received benefits from your employer like a company car or interest-free loan

If you’re a director of a limited company, it’s likely that you’re also registered as an employee and get paid a wage through Pay As You Earn (PAYE). That will be included in your return along with any other jobs.

I’m ready to complete my return – what happens next?

You can start the process by going to the Gov.uk website and signing in. Once you’re logged into your account, you can select Self Assessment and choose to complete your return.

Your personal Self Assessment page includes the deadline and how many days you have left to complete the assessment.

It’s possible to move between the different stages of the assessment process and save and return to complete details later.

How do I pay my Self Assessment tax bill?

Once your Self Assessment tax return has been filed, you need to pay your tax bill:

• sign in to your Government Gateway account

• navigate to "Self Assessment" to see the amount you owe.

• choose a payment method

The time you need to allow for the payment to clear before the 31 January deadline varies depending on how you pay.

Self Assessment payments that clear the same or next day:

• Bank transfer: Pay directly through your online bank account using HMRC's bank details, referencing your UTR number.

• Debit or credit card: Use the HMRC payment portal for online debit or corporate credit card payments.

• At your bank or building society: Visit a branch of your bank or building society, and make your payment there.

Payment methods that take three working days:

• Bacs bank transfer: Pay directly through your online bank account using Bacs.

• Direct debit: Set up a direct debit through your online HMRC account.

• By cheque: You can send a cheque by post to HMRC.

What happens if I can’t afford to pay?

It’s worth speaking to HMRC as soon as possible if you think you aren’t able to pay your tax – don’t bury your head in the sand!

HMRC’s Self Assessment general enquiries page explains your options for getting in touch.

HMRC's Time to Pay service allows people to spread tax payments over time. Self Assessment taxpayers with up to £30,000 of tax debt can do this online once they have filed their return.

If you owe more than £30,000, or need longer to pay, you should call the Self Assessment Payment Helpline on 0300 200 3822.

What are payments on account?

Payments on account are payments towards your next tax bill, which reflect how much HMRC expects you to make in the current tax year (remember you’re completing a tax return for income earned between 6 April 2024 and 5 April 2025).

Payments on account are designed to spread tax payments across the year, removing the burden of paying all the tax you owe in one go next time you file.

Let’s say you’re a freelance designer and your tax bill for the 2024-2025 tax year comes to £6,000.

HMRC assumes you’ll earn a similar amount in the 2025-2026 tax year. Instead of waiting until next January, HMRC asks you to pay half of next year’s tax in advance:

31 January 2026

• £6,000 for your 2024 to 2025 tax bill

• £3,000 first payment on account for 2025 to 2026

31 July 2026

• £3,000 second payment on account for 2025 to 2026

If your income drops and you know next year’s tax bill will be lower, you can apply to reduce your payments on account.

Not everyone who is self-employed has to follow the payments on account system. If your tax bill is £1,000 or less, you can just make a single tax payment. The same applies if more than 80% of your tax bill was paid via PAYE.

How can I keep accurate records?

Keeping accurate records is essential if you want to pay the correct amount of tax – and getting organised makes life a lot easier.

It’s essential to keep records of your income and expenses. That’s likely to include things like receipts, invoices and till rolls.

Downloading accounting software will help simplify the process.

Advice for filing your Self Assessment tax return

There are lots of resources if you need more help completing your tax return:

• book a free discovery call with an accountant in Enterprise Nation’s community

• watch HMRC’s videos on Self Assessment and access specialised advice for specific trades

• Chat to HMRC's digital assistant

• Read our guide on how to find last-minute help with your tax return

• contact HMRC's Self Assessment helpline on 0300 200 3310

HMRC warns that the helpline is usually extremely busy in January and business owners are encouraged to use online resources.