Do I have to complete a Self Assessment tax return?, image of a woman reviewing notes with a dog | Crunch

Of the many questions you’ll have when you first start to consider going self-employed, one unlikely to top your list is, “do I need to complete a Self Assessment?” It’s probably one of the most important ones, though.

Amongst all of the legal documentation that your business needs to operate successfully and within the law, a self assessment is one of the most important. This significant tax document is one that you’ll be dealing with when you’re self-employed, and if you’re not careful, it could be the one that causes you the most headaches. So let’s take a look at exactly what it is, whether you’ll need to file one, and why it’s important to stay on top of it.

What is a Self Assessment?

Simply put, a Self Assessment (or Form SA100) is HMRC’s way of finding out how much Income Tax and National Insurance you need to pay on any income which isn’t taxed at source. You can read more in our "What is a Self Assessment?" article, which details how to register with HMRC and the records you need to keep to complete your return.

Do I have to file a Self Assessment?

As a general rule, anyone who receives income that isn’t taxed at source needs to complete a Self Assessment.

In the case of a sole trader, the income you receive from your trade doesn’t have National Insurance Contributions or Income Tax deducted from it, so you need to tell HMRC about that income on a Self Assessment form so they can calculate what, if any, tax you owe.

If you’re a limited company director, you’ll usually need to file a Self Assessment to let HMRC know about any dividend income you’ve received form your company.

Other examples of income not taxed at source can include rental income from any property you own, income from abroad, or investment (dividend) income.

The complete list of who needs to complete a Self Assessment is available on the website – the website also has an online tool that will tell you if you need to file a return.


When do I need to fill in a Self Assessment?

You have to file your Self Assessment by 31st January after the end of the tax year it applies to. Tax years run from 6th April to 5th April. You don’t have to wait, though. If you’re employed, you can submit your Self Assessment as soon as you receive your Form P60 from your employer.

If you run your own company, you’ll need to issue the Form P60 from your PAYE system or get your accountant to prepare it for you. If you’re a sole trader then you can file your Self Assessment as soon as the tax year ends. There are lots of reasons why filing your Self Assessment early is a good idea.

What happens if I don't file my Self Assessment in time?

If you fail to notify HMRC, you may face a fine or penalty and will have to submit Self Assessments for prior tax years where applicable. If you’re unsure whether you’ve registered, you can contact HMRC with your National Insurance number on hand to confirm one way or another.

If you fail to submit your return once you’ve registered for Self Assessment, you can incur some fairly significant penalties (we’ve got more information on the fines and penalties in our article – Self Assessment: what happens if I miss the deadline?). HMRC are becoming increasingly strict on deadlines and penalties for late returns, so we can’t stress enough how crucial it is to get your Self Assessment filed on time.

Paying your Self Assessment tax bill

Sadly filing isn’t the end of the story, you’ll also need to ensure you pay any tax owed by the deadline of the 31st January.  HMRC will tell you how much tax you owe and you then hand over the cash, usually via Direct Debit or bank transfer (the full list of how you can pay is on the website). One last thing to remember is that since January 2018 you cannot use a personal credit card to pay your Self Assessment tax bill. You are also no longer able to pay your tax bill at the Post Office.

Don’t forget, you may also need to make a payment on account towards your next year’s tax bill. Our article “What is a payment on account and do I have to pay it?” explains more.

If you need more time to pay, we explain your options further in our article on late payment fees and fines.

We take the pain out of Self Assessments

At Crunch, we’re experts at looking after life’s numbers, so you can trust us to make your Self Assessment as worry-free as it can be. Our expert chartered certified accountants will take care of you, just like we did for over 7,500 clients in the last tax year. Speak to one of our advisers to see how we could help you keep on top of your finances.

Self Assessment service for Crunch clients

If you’re a Crunch client, our Crunch Personal Tax Service takes away all the headache and hassle of completing and filing your personal tax, we’ll prepare your Self Assessment and once you’ve approved it we’ll submit it online and let you know how much you need to pay HMRC. Our Crunch Premium package includes up to two Self Assessments for directors, or the service is available as a paid add-on for clients on our other packages.

Contact your client managers for more information or visit the ‘Personal Tax’ tab in your account.

You can find full details and pricing on our Self Assessment Service page.

Speak to an accounting expert

If you're unsure what level of support you need, our friendly team are on hand to help you pick the right package for you.
team photo off all crunch team
Share this post
Ross Bramble
Content Executive
Updated on
June 16, 2023

Knowledge Hubs

Speak to the experts

Our UK based team of experts are ready to help you find the best accounting package for you and your business.

icon of a green tick
Certified Accountants
icon of a green tick
HMRC Approved
Senior Sales Advisor
Book a meeting
Crunch Pro Tip
Using cloud-based accountancy software to manage your finances gives any small business a big advantage!

At Crunch we provide affordable cutting-edge, easy-to-use software with real human support from expert chartered accountants. That’s probably why 81% of our clients would recommend Crunch.

Crunch Pro Tip
Did you know - you have access to a Chartered Certified accountant for free on our paid subscriptions?

Book a call with our one accountants and get your questions answered. Just £24.50 +VAT for Crunch Free users.

Crunch Pro Tip
Did you know - Financial forecasting can allow you to predict any financial changes in your business and see the results of potential new ideas?

Our partnership with Brixx forecasting software gives our paid plan clients access to a financial forecasting tool for free.

Crunch Pro Tip
Did you know - Your Self Assessment has to be filed by the 31st of January deadline?

Crunch’s Self Assessment service provides an expert accountant to complete, check, and file your Self Assessment for you for just £140 +VAT.

Crunch Pro Tip
Did you know - We have a free plan that is great for sole traders and limited companies?

Why not see for yourself? It’s simple and easy to use and 100% free.