Filing a Self Assessment tax return can feel intimidating the first time — especially if you’re new to self-employment or earning additional income outside of PAYE. But with proper preparation and understanding, the process becomes straightforward and even empowering.
Whether you’re a freelancer, subcontractor, landlord, or company director, submitting your Self Assessment accurately and on time is essential to staying compliant with HMRC. In this article, we’ll guide you through every step of preparing for your first tax return — from registration to submission — and share tips for avoiding the most common mistakes.
1. What Is a Self Assessment Tax Return?
The Self Assessment system is how HMRC collects Income Tax from individuals who do not have it automatically deducted through PAYE.
This includes:
Sole traders and freelancers.
Partners in a business partnership.
Company directors receiving dividends.
Individuals earning rental or investment income.
Through Self Assessment, you report your total income and allowable expenses for the tax year (6 April to 5 April), and HMRC calculates how much tax you owe.
Even if you believe you’ve already paid enough tax through PAYE, you must still file if HMRC has requested one or if you’ve received untaxed income.
2. Registering for Self Assessment
If you’re new to self-employment, your first step is to register for Self Assessment with HMRC.
Here’s how the process works:
Visit the HMRC website and create a Government Gateway account.
Register as a sole trader or self-employed individual.
HMRC will issue you a Unique Taxpayer Reference (UTR) — a 10-digit code used to identify your tax record.
You’ll also receive an activation code for your online tax account.
You must register by 5 October following the end of the tax year in which you became self-employed.
Example: if you started trading in July 2024, you must register by 5 October 2025.
Failing to register on time can lead to penalties, even if you have no tax to pay.
3. Gathering the Right Information and Documents
Once registered, you’ll need to collect all relevant documents to complete your return accurately.
This includes:
Records of all self-employed income (invoices, receipts, and bank statements).
Details of other income (employment, rental, dividends, or savings).
Business expenses and receipts.
Your National Insurance number and UTR.
P60 or P45 forms (if employed during the year).
Pension contributions or charitable donations.
Keep in mind that HMRC requires you to keep accounting records for at least 5 years after the 31 January filing deadline.
If you use accounting software or an accountant, ensure your records are reconciled monthly. This makes year-end preparation significantly easier.
4. Claiming Allowable Expenses
A major benefit of Self Assessment is the ability to deduct allowable business expenses from your taxable income.
These can include:
Office supplies, stationery, and printing.
Phone, internet, and business-related software.
Travel and fuel costs (excluding commuting).
Professional subscriptions or insurance.
Marketing, advertising, and website hosting.
You can also claim a portion of home utility costs if you work from home, based on usage or HMRC’s simplified flat-rate allowance.
However, personal expenses are not deductible. Mixing personal and business costs can trigger HMRC scrutiny, so it’s best to maintain separate business accounts.
5. Calculating Income and Tax
Once all income and expenses are accounted for, you can calculate your taxable profit:
Total Income – Allowable Expenses = Taxable Profit
Your profits are then taxed according to current Income Tax and National Insurance thresholds.
For the 2024/25 tax year:
Basic rate (20%) applies up to £50,270.
Higher rate (40%) applies from £50,271 to £125,140.
Additional rate (45%) applies above £125,140.
You’ll also pay Class 2 and Class 4 National Insurance contributions based on your profit levels.
Using accounting software or working with a qualified accountant ensures these calculations are accurate and up-to-date with HMRC’s annual rate changes.
6. Filing Your Tax Return
Once ready, you can submit your Self Assessment online via the HMRC portal or through approved MTD-compatible software.
Key deadlines:
31 October – Paper return deadline.
31 January – Online submission deadline.
31 January – Payment due for your tax bill and first “payment on account” (if applicable).
HMRC will confirm your calculation instantly online. Always download a copy of your submission receipt and confirmation for your records.
If you miss the 31 January deadline, an automatic £100 penalty applies, followed by daily fines for prolonged delays. Interest is also charged on late payments.
7. Payments on Account Explained
One area that confuses many first-time filers is Payments on Account.
If your tax bill exceeds £1,000, HMRC assumes you’ll owe a similar amount next year and requires you to make two advance payments towards it:
First payment: 31 January (with your main tax bill).
Second payment: 31 July.
Each payment is 50% of your previous year’s tax bill.
When you file next year’s return, any overpayment will be credited or refunded automatically.
This system helps HMRC collect tax more evenly but can surprise first-timers, so it’s wise to budget early for these payments.
8. Common Mistakes to Avoid
First-time Self Assessment filers often run into the same pitfalls:
Missing registration deadlines (forgetting to apply for a UTR).
Not declaring all income sources.
Claiming disallowed expenses.
Failing to keep detailed records.
Leaving filing to the last minute.
Each mistake can lead to penalties or HMRC investigations. Staying organised throughout the year is far easier than trying to gather everything in January.
9. Professional Help or DIY?
While HMRC’s online system is user-friendly, many first-time filers prefer professional guidance — especially if they have multiple income streams or complex deductions.
An experienced accountant can:
Maximise your allowable expenses.
Ensure compliance with HMRC rules.
File on your behalf accurately and on time.
Handle correspondence if HMRC raises queries.
Think of it not as an expense, but as a risk prevention measure that saves time and potential penalties.
10. Final Thoughts
Filing your first Self Assessment doesn’t have to be stressful. With proper organisation, the right tools, and clear understanding, it becomes a manageable annual process.
Register early, track your income and expenses consistently, and never underestimate the value of professional guidance.
The key to success lies in preparation — not panic. By starting early and embracing digital recordkeeping, you’ll not only meet your obligations but gain greater control over your finances and confidence in your business growth.
