How to complete a Self-Assessment Tax Return – A step-by-step guide for SATR beginners
Filing a Self-Assessment Tax Return (SATR) can feel overwhelming, especially if you’re doing it for the first time. Whether you’re self-employed, a landlord, earning extra income from a side hustle, or a company director, you need to make sure your tax return is accurate, submitted on time, and as tax efficient as possible.
While it’s possible to do it yourself, mistakes can be costly- from overpaying tax to penalties from HMRC.
Here’s a step-by-step guide to completing your Self-Assessment and why working with a tax expert could be the best option for you…
Do I need to submit a Self-Assessment Tax Return?
Not everyone needs to complete a Self-Assessment, but you must file one if:
- You’re self-employed and earned over £1,000.
- You’re a landlord earning rental income.
- You have a side hustle, freelance income, or gig work outside your main job.
- You’re a company owner (unless 100% of your income is PAYE – in which case you may want to get a review on your current remuneration as this is likely not the most tax efficient way to pay yourself).
- You earn over £150,000, even if you’re fully employed.
- You earn over £60,000 and receive child benefit (due to the High-Income Child Benefit Tax Charge).
- You receive foreign income or untaxed savings/investments.
- You claim expenses that need to be reported via Self-Assessment.
💡 Not sure if you need to file? Contact our team for guidance – getting it wrong can lead to fines.
Do I need to register for Self-Assessment with HMRC?
If you haven’t filed a tax return before, you need to register with HMRC by 5th October following the tax year for which you were required to file a return.
- Register as self-employed (sole trader).
- Register as a landlord for property income.
- Register if you’re a director or receive untaxed income.
- HMRC will send you a Unique Taxpayer Reference (UTR)—you’ll need this to file.
💡 Missed the deadline? You could face penalties, so act quickly. We can help register you properly if you’d like support with registering for SATR.
Do I need documents and other information to support my tax return?
Filing your tax return is much easier if you have everything prepared. You’ll need:
- Your Unique Taxpayer Reference (UTR) and Government Gateway login
- Your National Insurance number
- A record of all income sources (self-employment, PAYE, dividends, rental income, investments)
- Business expenses you want to claim
- Your P60, P45, and possibly P11D if you also have employment income
- Details of any pension contributions or charitable donations
💡 Common mistake: Many business owners forget to keep proper records and miss out on allowable deductions. We can help ensure you claim everything you’re entitled to – and we send all our clients a personal tax organiser (just a small detail that makes SATR’s much easier for you!)
What expenses can I claim on my tax return?
One of the biggest advantages of working with an accountant is maximising tax relief on business expenses. You might be able to claim for:
- Office costs (rent, utilities, internet, phone bills)
- Travel expenses (mileage, train fares, accommodation)
- Marketing & advertising (website costs, social media ads, branding)
- Professional fees (accountants, solicitors, business insurance)
- Equipment & software (laptops, subscriptions, tools)
- Home office expenses (if you work from home, a portion of bills may be claimable)
💡 Warning: HMRC has strict rules on what qualifies as a business expense. An accountant ensures you claim the right things – without triggering an HMRC investigation (or a fine!)
When do I need to file and complete my online Tax Return?
Once you have all your information, log into your HMRC Self-Assessment account and start filling in the sections:
- Enter your income details (employment, self-employment, property, dividends, etc.)
- Input your business expenses
- Declare any pension contributions, benefits, or tax reliefs
- Double-check all figures to avoid errors
- Submit before the 31st January deadline
💡 Struggling with it? Even a simple mistake could cost you hundreds or result in fines. Let our tax experts handle it for you.
How do I pay my Tax bill? (can I set up a payment plan for my tax bill?)
After submitting your return, HMRC will calculate how much tax you owe. You’ll need to:
- Pay any tax due by 31st January (including any Payments on Account)
- Set up a payment plan by phoning HMRC, if you can’t afford to pay in full
- Check if you overpaid tax and are due a refund
💡 Missed the deadline? Late tax returns = automatic fines. We can help you avoid penalties and advise you on payment plans with HMRC.
Should I use an Accountant for my Self-Assessment Tax Return?
While it’s possible to file your Self-Assessment tax return yourself, it’s easy to make mistakes that result in overpaying tax or getting fined by HMRC. Here’s why working with a professional is a smart move:
- We ensure you claim every allowable expense – maximising your tax savings.
- We handle the complicated tax rules for you, avoiding HMRC penalties.
- We free up your time so you can focus on running your business.
- We help with tax planning, so you’re never caught off guard by big bills.
Need help with your Self-Assessment Tax Return?
Our expert team of accountants at BAS Associates take the stress out of tax returns – so you stay compliant, save money, and avoid costly mistakes. Get in touch today!
