Filing Your First Self Assessment Tax Return

Filing your first Self Assessment tax return can feel overwhelming. There are forms to complete, deadlines to meet, and penalties to avoid. But with the right preparation, it's a straightforward process that takes most people a few hours to complete.

This guide walks you through everything you need to know — from gathering your information to submitting your return online.

Before You Start

Make Sure You're Registered

Before you can file a tax return, you need to be registered for Self Assessment. If you haven't registered yet, you should have received:

A Unique Taxpayer Reference (UTR) — a 10-digit number
An Activation Code — sent separately by post

If you're missing either of these, you'll need to register first at GOV.UK. The UTR typically arrives within 10 working days of registration.

Create Your Government Gateway Account

To file online, you need a Government Gateway account. This is separate from your UTR registration.

Go to GOV.UK
Select "Create sign in details"
Provide your email address and create a password
You'll receive a User ID — keep this safe

If you already have a Government Gateway account (perhaps from claiming benefits or using other government services), you can use the same one.

Gather Your Information

Having everything ready before you start makes the process much faster. You'll need:

Income information:

Source	Documents needed
Employment	P60 (year-end summary), P45 (if you left a job), P11D (benefits)
Self-employment	Invoices, sales records, bank statements
Rental income	Rent received, letting agent statements
Savings interest	Bank/building society statements
Dividends	Dividend vouchers or statements

Expense records (if self-employed):

Receipts for allowable business expenses
Mileage logs if claiming vehicle costs
Home office calculations (if working from home)

Other information:

National Insurance number
UTR (10-digit reference)
Bank details (for refunds or Direct Debit payments)
Student loan plan type (if applicable)

Filing Online: Step by Step

Step 1: Log In to HMRC Online

Go to HMRC online services
Enter your Government Gateway User ID and password
Select "Self Assessment" from your account homepage
Click "Complete your tax return"

Step 2: Answer the Tailoring Questions

The first section asks about your circumstances to show only relevant parts of the form:

Did you receive income from employment?
Were you self-employed?
Did you receive rental income?
Did you have any savings or investment income?
Did you receive foreign income?

Answer honestly — saying "no" to something that applies to you could result in an incorrect return.

Step 3: Complete Each Section

Work through each section methodically. The main sections for most first-time filers are:

Personal details Check your name, address, and National Insurance number are correct. Update if needed.

Employment income Enter figures from your P60. If you had multiple employers, add each one separately. HMRC may have pre-filled some of this — check it matches your records.

Self-employment income Enter your total business income (turnover) and allowable expenses. You'll need to provide:

Your business name and description
Your accounting period (usually 6 April to 5 April)
Total income received
Total expenses claimed

Other income Add any other taxable income: savings interest above your Personal Savings Allowance, dividends, rental income, etc.

Step 4: Review Your Calculation

Once you've completed all sections, HMRC calculates your tax:

The system shows your total income and tax due
It accounts for your Personal Allowance and any tax already paid
You can see a breakdown of how the figure was calculated

Important: The calculation may show "Payments on Account" for next year. This is an advance payment towards next year's tax bill, usually half of your current year's liability. More on this in the "What to Expect After Filing" section.

Step 5: Submit Your Return

Before submitting:

Review all sections for accuracy
Check numbers match your records
Look for any warning messages or prompts

When ready:

Click "Submit" or "File return"
Read and accept the declaration
Note down your submission receipt number
Save or print the confirmation page

You'll also receive an email confirmation from HMRC.

What to Expect After Filing

Your Tax Bill

After submitting, you'll see exactly how much tax you owe. If this is your first Self Assessment, you might be surprised by "Payments on Account" — these are advance payments towards next year's bill.

Payment	Due date	What it covers
Balancing payment	31 January	Tax owed for the year you just filed
First payment on account	31 January	50% of next year's estimated tax
Second payment on account	31 July	Remaining 50% of next year's estimated tax

Example: If your tax bill is £3,000 for 2024/25, you'd pay:

£3,000 (balancing payment) — by 31 January 2026
£1,500 (first payment on account) — by 31 January 2026
£1,500 (second payment on account) — by 31 July 2026

That's £6,000 in your first year. The good news is that payments on account reduce your bill the following year.

Getting a Refund

If you've overpaid tax (perhaps through your PAYE job), you may be due a refund. HMRC will:

Process refunds within a few weeks of submission
Pay directly to your bank account (if you've provided details)
Send a cheque if no bank details are on file

Common First-Timer Concerns

"What if I make a mistake?"

If you realise you've made an error after submitting, you can amend your return online for up to 12 months after the filing deadline. After that, you'll need to write to HMRC.

"What if I don't have all my records?"

Use the best estimates you can from bank statements and other sources. HMRC understands that perfect records aren't always available, especially for first-time filers. Just be reasonable and consistent.

"What if I can't pay the full amount?"

If you can't pay by 31 January, you have options:

Set up a Time to Pay arrangement online (for bills up to £30,000)
Contact HMRC to discuss a payment plan
Pay what you can — even partial payment reduces interest and penalties

Don't ignore the deadline — the penalties for not paying are separate from penalties for not filing.

"Do I need an accountant?"

For straightforward self-employment with minimal expenses, most people can file themselves. Consider professional help if:

Your affairs are complex (multiple income sources, capital gains)
You're not confident with numbers
Your business has significant expenses to optimise
You want to save time

Tips for a Smoother Process

Don't leave it until January — File early to know what you owe and plan accordingly
Save as you go — The online system lets you save and return later. You don't need to complete everything in one sitting
Use the HMRC app — You can check your tax position and make payments via the free HMRC app
Keep a copy — Download or print your completed return for your records
Note the deadlines — For 2024/25 tax year:
- Online filing deadline: 31 January 2026
- Payment deadline: 31 January 2026

What About Paper Returns?

You can still file on paper, but the deadline is earlier — 31 October instead of 31 January. Most people file online because:

It's faster and easier
You get an immediate calculation
The deadline is three months later
You receive instant confirmation

To file on paper, request form SA100 from HMRC or download it from GOV.UK.

This guide is for informational purposes only and does not constitute tax, legal, or financial advice. Tax rules change frequently. Always verify current requirements on GOV.UK or consult a qualified accountant for your specific situation.

Official Sources

Self Assessment tax returns - GOV.UK
File your Self Assessment tax return online - GOV.UK
Understand your Self Assessment tax bill - GOV.UK
Pay your Self Assessment tax bill - GOV.UK