Self Assessment for First-Time Filers: A Beginner’s Guide

Step 1: register

Tell HMRC you need to file as soon as your income starts, for example when you start trading or receive rental income. You will receive a UTR by post.

Step 2: keep records

Record income and costs from day one. Even a simple spreadsheet with receipts is enough to begin with.

Step 3: file and pay

Complete the return online, check the calculation and pay by 31 January. Set aside part of each payment you receive, around 20% to 30% of profit is a common starting point.

First-year surprises

Your first bill can include the previous year’s balance plus the first payment on account, which feels like paying twice. It is a timing effect rather than extra tax.

Step by step: how a first Self Assessment return works

Filing for the first time feels daunting mainly because the process has several stages that are spread over months. Understanding the order helps. The tax year runs from 6 April to 5 April. You need to tell HMRC you need to file by 5 October after the end of the tax year in which you first had untaxed income. HMRC then issues a Unique Taxpayer Reference (UTR) by post, which can take around 10 working days, and longer if you live abroad. You then activate your online Government Gateway account using a code sent separately by post, so it pays to register early rather than in January.

The deadlines are: 5 October to register, 31 October for a paper return, and 31 January for an online return and for paying the tax due. If you are required to make payments on account, the second instalment falls on 31 July. Missing the 31 January filing deadline brings an immediate £100 penalty, even if you owe no tax.

What you will need to hand

• Your National Insurance number and UTR.
• Records of income and expenses for the tax year, such as invoices, bank statements and receipts.
• Details of any other income: employment (P60 or final payslip), savings interest, dividends, rental income or capital gains.
• Details of pension contributions, Gift Aid donations and student loan plan, if relevant.

Which expenses and allowances can you use?

If you are newly self-employed, you can either deduct your actual allowable business expenses or use the £1,000 trading allowance, but not both. The allowance is simple, and it often suits people with small side incomes. The same £1,000 limit applies separately to property income. Where gross income is £1,000 or less, it may not need to be reported at all, though check current HMRC guidance for your circumstances.

Worked example: a first return for a freelancer

This is an illustrative example. A freelancer started working in the 2025/26 tax year, with income of £14,000 and expenses of £2,500, and no other income.

No tax is due, but the return must still be filed. Because profit is above the Small Profits Threshold of £6,845, the freelancer is treated as having paid Class 2 National Insurance for State Pension credit purposes. Below that figure they could choose to pay voluntary Class 2, about £3.50 a week in 2025/26, to protect their record.

Now consider a different example: a person with £2,400 of side income and £600 of real expenses. Using actual expenses gives profit of £1,800. Using the trading allowance gives £2,400 – £1,000 = £1,400. The allowance is better here, so it would normally be chosen.

Common mistakes first-time filers make

• Leaving registration until after 5 October and then waiting for the UTR to arrive.
• Waiting until January to start gathering records.
• Claiming both the trading allowance and expenses.
• Assuming that no tax due means no return is needed.
• Forgetting savings interest, dividends or a small amount of other income.
• Missing the tax bill, which is due on the same day as the return, 31 January.

First-time filer checklist

1. Register with HMRC and note the 5 October deadline.
2. Activate your Government Gateway account when the code arrives.
3. Record income and expenses as you go.
4. Decide between expenses and the trading allowance.
5. File online and pay by 31 January, then keep records for five years after that deadline.

Helpful guides: registering late after 5 October, setting up your Government Gateway account, the SA100 form explained and a first-year self-employed tax guide. Our Self Assessment for sole traders page explains the service in full.

SATR is a trading style of Accotax. We help first-time filers with registration, records and the return itself: qualified UK accountants, filed online, for a fixed fee from £199 + VAT.

This is general information, not personal tax advice.

Planning your first year of tax

The first return is also the moment to build habits that make later years easier. Open a separate bank account for business income and spending if you can, because it makes the figures far easier to check. Record each invoice and receipt weekly or monthly, rather than leaving it until January. Put aside a share of every payment you receive: many new filers find that setting aside around 20% to 30% of profit, depending on income level

The Bottom Line

Filing your first Self Assessment tax return is a significant milestone. Understanding the registration process, key deadlines, and allowable expenses from the outset helps you avoid costly penalties and ensures you claim everything you’re entitled to. With the right preparation, your first return can be straightforward.

Our fixed-fee Self Assessment tax return service is £199 + VAT. Order now or get an instant quote.

, avoids a nasty surprise. If your tax bill for the year is more than £1,000, remember that payments on account may apply from the following year, which means a larger January payment the first time. Our guide to [[self-assessment-payments-on-account-explained|payments on account]] explains how this works.

Finally, keep a copy of your return and a note of how you worked out each figure. HMRC can ask questions about a return for a period after you file, and clear records make any enquiry far less stressful.

Frequently asked questions

Can an accountant do my first return?

Yes. A fixed-fee service means you know the cost before you start.

What if I started in the middle of the year?

You file for the tax year in which you started and report income from the start date.

How long does it take to get a UTR?

It usually takes around 10 working days by post, and longer if you live abroad. Your Government Gateway activation code is sent separately, so allow time for both before the deadline.

Do I have to file if I owe no tax?

If you are required to submit a return, you must file by the deadline even if no tax is due. A late return brings a £100 penalty from day one.

Can I file my first return myself?

Yes, many people do. An accountant can help if your affairs include expenses, several income types or capital gains, and want certainty that the return is correct.