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Start filing →If you've never filed a Self Assessment tax return before, it can feel daunting. It doesn't need to be. This guide explains everything from scratch — what Self Assessment is, whether you need to file, and exactly how to do it.
What Is Self Assessment?
Self Assessment is HMRC's system for collecting tax on income that hasn't been automatically taxed through an employer. If you are employed, your employer deducts tax via PAYE. But if you have other income — from self-employment, rental property, dividends, or other sources — you need to declare it yourself through a Self Assessment tax return.
Who Needs to File Self Assessment?
You need to file if any of the following applied in the last tax year:
- You were self-employed and earned over £1,000
- You had rental income from a property
- You earned over £100,000 in total
- You received dividends from company shares
- You had untaxed income over £2,500
- You claimed Child Benefit and your income was over £60,000
- You are a company director
- You lived or worked abroad and had UK income
What Do You Need Before You Start?
| Document | What it contains |
|---|---|
| UTR number | Your 10-digit Unique Taxpayer Reference from HMRC — required to file |
| NI number | Your National Insurance number — on your payslip or P60 |
| P60 | From your employer — shows salary earned and tax paid |
| Self-employment records | Total income received, allowable expenses |
| Bank interest | From your bank statements |
| Rental records | Rent received, mortgage interest, expenses |
The Self Assessment Process Step by Step
Register for Self Assessment
Go to HMRC's website and register. HMRC will send your UTR (Unique Taxpayer Reference) by post within 10 days. Do this by 5 October after the end of the tax year you need to declare.
Gather your income information
Collect all your income figures for the tax year: P60 from employer, self-employment income, rental income, dividends, savings interest. Add up your allowable expenses too.
Complete your return
Use SubmitFox to work through your return. It asks plain-English questions and calculates your tax automatically. You can save progress and come back to it.
Review and submit
Check your tax calculation, make sure everything looks right, then submit directly to HMRC. You'll receive instant confirmation.
Pay what you owe
Any tax owed must be paid by 31 January. You can pay via bank transfer, debit card, or through your HMRC account.
File your first Self Assessment with SubmitFox
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Common Questions
Yes. Your Unique Taxpayer Reference (UTR) is a 10-digit number that HMRC uses to identify your tax records. If you have never filed before, you must register with HMRC first — they will post your UTR to you within 10 working days.
Most first-time filers with straightforward income take 30 to 60 minutes. The main time is spent gathering documents (P60, income records, expense receipts). The actual filing process with SubmitFox typically takes 15 to 20 minutes once you have your information.
SubmitFox is designed with first-time filers in mind — each question includes a plain-English explanation of what is being asked and why. If you are still unsure, the HMRC Self Assessment helpline (0300 200 3310) can clarify specific questions.
Not necessarily. Many first-time filers owe little or no tax, particularly if they are under the personal allowance or their expenses significantly reduce their profit. SubmitFox shows you your tax calculation before you submit so there are no surprises.
If you registered after the 5 October deadline, HMRC may issue a penalty. However, if this is your first year and you registered as soon as you realised you needed to, you can appeal the penalty by explaining the circumstances. File as soon as you have your UTR.