First Time Doing Self Assessment: A Beginner's Step-by-Step Guide

Filing your first Self Assessment tax return can feel daunting. But with the right preparation and guidance, it’s straightforward. Here’s everything you need to know to complete your first return successfully.

What is Self Assessment?

Self Assessment is HMRC’s system for collecting income tax from people whose tax isn’t fully handled by employers through PAYE. You “assess” your own income and tax owed, then HMRC collects it.

You might need Self Assessment because you’re:

• Self-employed or freelancing
• A landlord receiving rental income
• Earning over £150,000
• Receiving significant dividend income
• A company director
• Liable for High Income Child Benefit Charge

👉 Do I need to do a tax return?

First-Time Timeline Overview

Paper returns: If you prefer paper, the deadline is 31 October 2026 — but online is easier.

Step 1: Register for Self Assessment

You must register before you can file. Don’t leave this until January — it takes time to receive your Unique Taxpayer Reference (UTR).

How to Register

1. Go to gov.uk/register-for-self-assessment

2. Sign in with Government Gateway (create an account if needed)

3. Choose your registration type:

   • Self-employed — if you run a business, freelance, or do contract work
   • Not self-employed — if you have rental income, investments, or other untaxed income
   • Partner in a partnership — if you work with others as business partners

4. Enter your personal details:

   • Full name
   • National Insurance number
   • Date of birth
   • Address
   • Phone number
   • When you started trading (if self-employed)

5. Submit and wait for your UTR

Getting Your UTR

HMRC posts your 10-digit Unique Taxpayer Reference within 10 working days. This is essential — you can’t file without it.

If you don’t receive it within 3 weeks:

• Check your junk mail (if registered for online correspondence)
• Phone HMRC on 0300 200 3310
• Have your National Insurance number ready

Step 2: Gather Your Records

Before you start filling in forms, collect everything you need:

If You’re Self-Employed

If You’re Employed Plus Self-Employed

If You Have Rental Income

Other Information You May Need

Step 3: Access the Online System

Create a Government Gateway Account (If New)

1. Go to gov.uk/log-in-register-hmrc-online-services
2. Create an account with your email
3. You’ll receive a 12-character User ID — save this somewhere safe
4. Set up your password and security questions

Enrol for Self Assessment

1. Sign into Government Gateway
2. Select “Add a tax” or “Enrol for a service”
3. Choose “Self Assessment”
4. Enter your UTR and National Insurance number
5. Complete identity verification

Identity verification may require:

• Your passport details
• Information from your credit file
• Or waiting for an activation code by post (5-7 days)

Step 4: Complete Your Tax Return Online

Once enrolled, you can start your return. Here’s what to expect:

Main Sections

Tips for Each Section

Tailoring Your Return

The first step asks which income types you have. Only tick what applies to you - this determines which sections appear. Common selections:

• ✅ Were you an employee or company director?
• ✅ Were you self-employed?
• ✅ Did you receive income from UK property?
• ✅ Did you receive UK interest or dividends?

Self-Employment Section

For most first-timers, this is the most complex part. You’ll enter:

Income:

• Total turnover (sales) for the year

Expenses (choose one method):

• Actual expenses — itemise everything you spent on the business
• Simplified expenses — use HMRC flat rates for vehicles, home working, etc.

Common allowable expenses:

Simplified Expenses Option:

If you work from home or use your personal vehicle, simplified expenses may be easier:

Property Section

Enter:

• Total rent received
• Allowable expenses (repairs, insurance, letting agent fees, etc.)
• Or claim the £1,000 Property Allowance if that’s higher than your expenses

Note: Mortgage interest relief is now limited to 20% tax reduction, not deductible from income.

Savings and Dividends

Enter the amounts from your bank/broker statements. The system calculates whether they exceed your:

• Personal Savings Allowance (£1,000 basic rate / £500 higher rate)
• Dividend Allowance (£500)

Step 5: Review and Submit

Before submitting:

1. Check the summary: HMRC shows your total income, deductions, and tax owed
2. Review each section: Ensure figures match your records
3. Look for obvious errors: Wrong figures, missing income, double entries
4. Make a note of the tax owed: You’ll need to pay this by 31 January

When ready:

1. Click “Submit return”
2. You’ll receive an acknowledgement with a reference number
3. Save or print this for your records

Step 6: Pay Your Tax Bill

Payment Deadline

Tax owed must be paid by 31 January — the same deadline as filing.

Payment Methods

Payment reference: Use your UTR plus the tax year (e.g., “1234567890K” for 2025/26).

Payments on Account

If your tax bill exceeds £1,000 and less than 80% is collected at source (PAYE), you’ll also need to make “Payments on Account” — advance payments toward next year’s tax:

Example: Your 2025/26 Self Assessment bill is £3,000. On 31 January 2027, you pay:

• £3,000 (2025/26 tax owed)
• £1,500 (first Payment on Account for 2026/27)
• Total: £4,500

This catches many first-timers by surprise. Budget for it.

Common Mistakes to Avoid

1. Missing the Registration Deadline

Register by 5 October. If you wait until January, you won’t have your UTR in time.

2. Forgetting to Include All Income

Everything must be declared:

• All employment income (including previous jobs)
• Side hustle income
• Cash payments
• Foreign income
• Investment income

HMRC receives data from banks, employers, and platforms — they know more than you think.

3. Claiming Personal Expenses as Business

Only expenses “wholly and exclusively” for business are deductible. Personal costs (commuting, regular meals, clothing) don’t count.

4. Not Keeping Records

Keep receipts and records for at least 5 years. HMRC can investigate previous returns — without records, you can’t prove your claims.

5. Entering Wrong Figures

Double-check totals before submitting. A simple typo could mean over/underpaying tax.

6. Forgetting Payments on Account

Budget for 150% of your first year’s tax bill if you owe more than £1,000. The surprise second payment catches many people out.

What If I Need Help?

Free Help

• HMRC helpline: 0300 200 3310 (Self Assessment queries)
• HMRC YouTube: Tax return walkthrough videos
• Citizens Advice: Free guidance on tax matters
• TaxAid: Free tax advice for people on low incomes

Paid Help

• Accountant: £150-400 for a simple return, more for complex affairs
• Tax software: FreeAgent, QuickBooks, Xero — automates much of the process

For your first year, if your situation is straightforward (sole trader, simple income), try doing it yourself. The learning experience is valuable. If you have multiple income sources, property, or overseas affairs, professional help may save time and worry.

After You Submit

Keep Confirmation

Save or print your submission receipt showing:

• Date and time submitted
• Reference number
• Summary of figures

Watch for HMRC Contact

If HMRC queries your return, they’ll contact you. Check letters and your Personal Tax Account regularly.

Set Up for Next Year

Use this year’s experience:

• Create a system for tracking income and expenses throughout the year
• Set aside tax money monthly (aim for 25-30% of profits)
• File early next year to avoid the January rush

Key Takeaways

• Register early — you need your UTR before you can file (up to 10 days to arrive)
• Gather records first — income, expenses, P60, bank statements
• Use HMRC’s online system — it guides you through each section
• Declare all income — HMRC receives information from many sources
• Budget for Payments on Account — your first January bill may be 150% of the tax owed
• Keep records for 5 years — HMRC can investigate historical returns
• File early — avoid January stress and get more time to arrange payment
• Mistakes happen — you can amend within 12 months of the deadline

This guide covers the basics for first-time Self Assessment filers in 2026/27. Complex circumstances may require professional advice. This is not tax advice.