10 min read
If you’ve recently gone self-employed, started freelancing, renting out a property, or picked up a side hustle—you’re now required to complete a Self Assessment tax return.
It might sound intimidating at first. HMRC, UTRs, allowable expenses… where do you even begin?
Take a deep breath. Filing your tax return is easier than you think—especially when you break it down step by step.
This blog is written for absolute beginners. By the end, you’ll know exactly what to do and when to do it. Let’s get started.
What is Self Assessment and who needs to file?
A Self Assessment tax return is how you tell HMRC about your income and pay any tax you owe.
If you’re employed, tax is usually taken automatically through PAYE (Pay As You Earn). But if you’re earning money in other ways, you’ll probably need to submit a tax return yourself.
You need to file if:
- You’re self-employed or a sole trader earning over £1,000/year
- You rent out a property You receive untaxed income from savings, dividends, or overseas work
- You want to claim tax relief (e.g. on pensions or donations)
- You’ve made gains from selling shares, property, or other assets
- If you receive child benefit and fall in the higher tax bracket
If any of these apply to you, it’s important to understand how the Self Assessment process works.
How to file your tax return in 5 easy steps?
Now, let’s go through the steps to submit your tax return.
Step 1: Register with HMRC
If you’re new to Self Assessment, registering with HMRC is the first step. This tells them you have untaxed income to report.
If you earned untaxed income between 6th April 2024 and 5th April 2025, you must register by 5th October 2025.
Once registered, HMRC will post your Unique Taxpayer Reference (UTR) — a 10-digit number that identifies you for all your tax affairs. You’ll need this whenever you contact HMRC or submit a tax return.
You’ll also set up your Government Gateway login. This is your secure HMRC online account, which lets you submit your tax return, check your tax records, and manage payments.
What if you miss the deadline?
You can still register, but HMRC will give you a different filing deadline—usually three months from the date of their letter or email.
However, you still must pay any tax owed by 11:59 pm on 31st January 2026. Missing this deadline means automatic penalties and possible interest, even if HMRC gave you extra time to file.
Step 2: Get your information together
Now the admin and paperwork begins (but not too much if you stay organised). Make sure you have:
Personal info:
- National Insurance number
- UTR
- Government Gateway login
Income details:
- Self-employed income (sales records, invoices)
- PAYE income (P60 or P45)
- Rental income and expenses
- Bank interest
- Dividends
- Pension or benefits
- Overseas income (if applicable)
Expenses you can claim (if self-employed):
- Office/stationery costs
- Phone and internet
- Travel or mileage
- Home office use
- Software subscriptions
- Marketing/advertising
Keeping accurate records all year will make this step much easier.
Step 3: File online
HMRC’s online portal is the fastest and easiest way to file. Go to gov.uk, log in with your Government Gateway ID, and choose the correct tax year.
You’ll be guided through a series of questions. HMRC will only show you the sections that apply to your situation.
There’s no need to rush—take your time.
Step 4: Complete your return
Here’s what you’ll see on the form.
1. Personal details
Confirm your name, address, NI number, and UTR.
2. Employment income
Add figures from your P60 if you also had a regular job.
3. Self-employment
Report your business turnover, expenses, and net profit. You may be able to use simplified expenses (a flat-rate method for mileage and home use).
4. Property income
Landlords must report:
- Total rent received
- Mortgage interest and property-related expenses
- Profit from letting
5. Other income
Include:
- Bank interest
- Dividends
- Capital gains
- Overseas earnings
6. Tax relief
This is where you enter things like:
- Gift Aid donations
- Pension contributions
- Student loan repayments
which will be offset against your income to reduce the amount of tax you need to pay. This is all calculated on the Government online form.
Step 5: Submit and pay
Submit your return online when you’re ready — no need to overthink it. HMRC will review it and let you know how much to pay by 31 January 2026.
What are “Payments on Account”?
If your bill is over £1,000, HMRC may ask for Payments on Account. These are advance payments towards next year’s tax.
They’re split into two equal payments:
- 50% due by 31st January
- 50% due by 31st July
A lot of first-timers get caught off guard by this—so be sure to plan for it.
What if you can’t pay right away?
Don’t panic. If you’re struggling to pay your bill, contact HMRC as soon as possible. You may be able to set up a payment plan using their Time to Pay service.
Note that you should always file your return on time—even if you can’t pay right away. This helps you avoid late filing penalties, which are separate from late payment fines.
Step 6: Avoid common mistakes
Simple errors can cause stress and cost you money. Watch out for:
- Missing the deadline: File by 31st Jan (online) or 31st Oct (paper).
- Guessing figures: Always use actual records—not estimates.
- Forgetting reliefs or expenses: You could end up overpaying tax.
- Not saving a copy: Always download a PDF for your records.
Penalties: What happens if you're late?
Even if you don’t owe tax, late filing means:
- £100 fine the day after the deadline
- After 3 months: £10 per day, up to 90 days
- After 6 months: Extra £300 or 5% of tax due
- And more interesting if you still haven’t paid
Filing early is always better—you’ll avoid penalties and reduce stress.
Key dates for your diary
Mark these important Self Assessment deadlines to stay on track and avoid penalties.
What | Deadline |
Register for Self Assessment if doing it for the first time | 5th October 2025 |
Submit paper return | 31st October 2025 |
Submit online return | 31st January 2026 |
Pay tax owed | 31st January 2026 |
2nd payment on account (if due) | 31st July 2026 |
Should you get an accountant?
If your finances are simple, you can probably manage without one.
But if you have:
- Multiple income sources
- Overseas income
- Rental portfolios
- Capital gains
- Complicated deductions
…it’s worth getting professional advice. An accounting expert can help you save money, reduce errors, and stay compliant.
Tips to make it easier next time
A little planning now makes next year’s Self Assessment far less stressful.
- Keep good records all year round
- Use accounting software (even free tools work well)
- Set aside 20–30% of your income for tax
- Don’t leave it until January to start
- Ask questions if you get stuck
Even a bit of early planning can make your next return a breeze.
Conclusion
Filing your first Self Assessment return can feel like a big task—but it’s manageable with the right steps.
Register early, track your income and expenses, and don’t leave it until the last minute. Filing on time avoids unnecessary penalties.
If you need a hand or just want a little guidance, we’re always happy to help. Contact us today and get the support you need to file with confidence.
