To file your tax return online in the UK, you’ll need to follow these simple steps:

1. The first step is to sign onto the GOV.UK website if you’re registered. If you’re not registered, you’ll first need to do so. 

   a. Apart from being registered, you’ll also need your unique taxpayer reference (UTR), National Insurance number, a valid email address, and an employer reference if you have one.

2. Once logged into your account, you can start completing the tax return form online. Here, you’ll provide details about your income and expenses. When completing the form, there are a few things to keep in mind: 

   a. You don’t need to complete the form in one sitting. You can save your progress and return to the document later. 

   b. You shouldn’t send any documents to support your self-assessment if the HMRC does not ask you to do so.  

3. After you’ve completed the form, but before submitting it, you should carefully check all the information to ensure that it’s correct and that you’ve included everything you need. Remember, you accept responsibility for all the information provided. Luckily, if you encounter any challenges, you can always contact the HMRC helpline to ask for help.

4. If you’re satisfied that all the information you’ve provided is correct, you can submit your tax return online. The online platform will calculate your tax liability based on this information.

5. You’ll then need to pay any tax you owe to HMRC before the deadline, typically at the end of January every year. If you cannot pay any outstanding tax in full, you can set up a payment plan with HMRC.

The process itself is straightforward. However, it gets complicated when deciding where to file which expense and income. For example, can you deduct Item A? Can you deduct Item B? 

It all depends on the nature of your business, so you’ll either need to be acquainted with bookkeeping or consider Outmin, where you’re paired with experts who do all your accounting for you (including filing tax returns), starting from £199/month.