Self-Employed First Tax Return 2026: A Beginner's Guide

Quick answer

Your first Self Assessment can feel daunting, but the process is logical once you break it down. You register with HMRC to get a Unique Taxpayer Reference, keep records of your income and expenses, file a return online by 31 January after the tax year ends, and pay income tax plus Class 4 National Insurance on your profits. On top of that, the new Making Tax Digital for Income Tax regime is now phasing in, changing how the highest-earning sole traders and landlords report. This guide takes you through each step in order so nothing catches you out.

Step 1: Do you actually need to file?

You need to complete a Self Assessment return if, in the tax year, you were self-employed as a sole trader and earned more than £1,000 (the trading allowance), among other triggers. If your self-employed income was under £1,000, the trading allowance usually means you have nothing to declare. Other common reasons to file include untaxed income, rental income, or being caught by the High Income Child Benefit Charge. Our guide on whether you need to file covers every trigger.

Step 2: Register and get your UTR

Before you can file, you need to register for Self Assessment with HMRC. Registration:

• Must be done by 5 October following the end of the tax year in which you started trading. Miss it and you can face a "failure to notify" penalty.
• Generates your Unique Taxpayer Reference (UTR) — a 10-digit number you need for every return.
• Sets up your Government Gateway account for online filing.

The UTR arrives by post within about 10 working days, and a separate activation code follows, so do not leave registration to the last minute. Register as a sole trader specifically — this also enrols you for Class 2 and Class 4 National Insurance where relevant.

Step 3: Know your deadlines

There are three dates that matter for your first return:

• 5 October (after the tax year ended): deadline to register if you have not already.
• 31 October: deadline for a paper return (rarely used now).
• 31 January (after the tax year ended): deadline to file online and pay the tax due.

So for the 2025/26 tax year (6 April 2025 to 5 April 2026), you register by 5 October 2026 and file and pay by 31 January 2027. Missing the January deadline triggers an automatic £100 penalty, with more added the longer you delay — so diarise it early.

Step 4: Work out your taxable profit

Your tax is based on profit, not turnover. Profit is:

Business income − allowable expenses = taxable profit

You then have a choice of accounting basis, and you can claim either actual expenses or simplified flat-rate amounts for things like vehicle mileage and working from home. Getting expenses right is where many first-timers either overpay tax or, worse, over-claim and risk a query.

Allowable expenses

Common allowable expenses for a sole trader include:

• Office costs, stationery and phone/internet used for business.
• Travel for business (not commuting), including a mileage rate for your own vehicle.
• A proportion of home costs if you work from home.
• Stock, materials and tools.
• Professional fees, insurance, and accountancy costs.
• Bank charges and interest on business borrowing.

The golden rule is that an expense must be wholly and exclusively for the business. Keep every receipt and record from day one. Our allowable expenses guide goes through the categories in detail.

Step 5: Understand the tax and NI you'll pay

As a sole trader you pay two things on your profits.

Income tax

Profit is taxed after your personal allowance of £12,570 (2026/27):

• 20% on profit in the basic-rate band up to £50,270.
• 40% on profit in the higher-rate band above £50,270.
• 45% on profit above the additional-rate threshold.

Class 4 National Insurance

On top of income tax, you pay Class 4 NI on profits above the lower threshold, charged as a percentage of profits up to the upper limit and a lower percentage above it. Class 2 NI rules have changed in recent years — for most, Class 2 is no longer a flat weekly charge but profits above the small-profits threshold still secure your NI record for the State Pension. Estimate the combined bill with the

, and see your overall take-home with the .

Step 6: Brace for payments on account

This is the single biggest surprise for first-time filers. If your tax bill is over £1,000, HMRC asks you to make payments on account — advance payments towards next year's bill. In your first January you may have to pay:

• The full tax due for the year just ended, plus
• A first payment on account of 50% of that bill towards the next year.

So your first bill can effectively be 150% of one year's tax. A second payment on account follows on 31 July. It feels brutal, but it is bringing you onto the same footing as PAYE employees who pay as they go. After the first year it smooths out. Our deadline guides explain the mechanics so there are no surprises.

Step 7: Get ready for Making Tax Digital (MTD ITSA)

The biggest change on the horizon is Making Tax Digital for Income Tax Self Assessment (MTD ITSA). Instead of one annual return, affected sole traders and landlords must:

• Keep digital records of income and expenses using MTD-compatible software.
• Send HMRC quarterly updates of their figures.
• Submit a final declaration after the tax year to confirm the full position.

MTD ITSA is being phased in from April 2026, starting with the highest earners (those with qualifying self-employment and property income above the top threshold), with lower income thresholds brought in over the following years. If your gross self-employment and property income is high, check whether you are in the first wave — you may need to start keeping digital records and filing quarterly rather than relying on the familiar single January return. Even if you are not yet in scope, adopting bookkeeping software now makes the eventual transition painless.

Step 8: File the return

When it comes to filing, you log into your Government Gateway account, complete the self-employment pages (and any other sections that apply, such as employment or rental income), enter your income and expenses, and HMRC calculates the tax. You then pay by the 31 January deadline. Keep your records for at least five years after the filing deadline in case HMRC asks to see them.

A first-year worked example

Aisha starts freelancing in the 2025/26 tax year and makes £35,000 profit after expenses.

• She registers by 5 October 2026 and gets her UTR.
• Income tax: profit above the £12,570 allowance is taxed at 20%, giving roughly £4,486.
• Class 4 NI adds a further charge on profits above the threshold.
• Her total bill is over £1,000, so in January 2027 she pays the full year's tax plus a 50% payment on account for 2026/27, with a second payment due in July 2027.

Had Aisha set aside 30% of every invoice from the start, the January bill would have been comfortably covered. Run your own numbers through the

and the .

Choosing your accounting basis

When you fill in your first return you record income and expenses on one of two bases, and the default changed recently:

• Cash basis — you count income when money actually reaches you and expenses when you actually pay them. It is simple, intuitive and now the default for most sole traders. Cash flow and tax line up neatly, which suits small and growing businesses.
• Traditional (accruals) basis — you record income when invoiced and expenses when incurred, regardless of when cash moves. This is more complex but can suit larger businesses or those carrying stock and giving credit.

For most first-time sole traders the cash basis is the sensible choice because it is easier and matches how you experience your money. You can opt out and use traditional accounting if it suits your business better. Whichever you pick, apply it consistently and keep clear records to back up the figures.

Common first-year mistakes to avoid

A few errors trip up almost every new sole trader. Forewarned is forearmed:

• Forgetting payments on account, then being blindsided by a bill of up to 150% of one year's tax in January.
• Mixing personal and business money in one account — open a separate business account from day one so your records are clean and defensible.
• Over-claiming expenses that are not wholly and exclusively for the business, which can invite an HMRC enquiry.
• Under-claiming legitimate expenses (mileage, use of home, equipment) and paying more tax than you need to.
• Leaving registration or filing to the last minute, risking failure-to-notify and late-filing penalties.
• Not setting tax money aside as income arrives, then having no cash to pay the bill.

Should you use an accountant?

You are not required to use an accountant — many sole traders file perfectly well themselves, especially with bookkeeping software. But in your first year, a good accountant often pays for themselves by ensuring you claim everything you are entitled to, structure things sensibly, register on time, and avoid penalties. Their fee is itself an allowable expense. As your turnover grows, the question of whether to incorporate as a limited company also arises, which is a decision where professional advice is especially valuable. If you stay a sole trader and your affairs are straightforward, you may comfortably handle the return yourself once you have the routine established. Either way, understanding the process — as set out here — keeps you in control.

First-return checklist

• Register for Self Assessment as a sole trader and get your UTR (by 5 October).
• Set up a Government Gateway account.
• Keep digital records of all income and expenses from day one.
• Put aside 25–30% of income for tax and NI as you go.
• Diarise 31 January for filing and payment, and 31 July for the second payment on account.
• Check whether MTD ITSA applies to you and adopt compatible software early.
• Keep records for at least five years.

The bottom line

Your first self-employed tax return is mostly about getting organised early: register on time, keep clean records, claim your legitimate expenses, and set money aside as you earn so the January bill — payments on account included — does not bite. With MTD ITSA now phasing in from April 2026, adopting digital bookkeeping now is the smartest move you can make. Estimate your liability with the

and your take-home with the , and lean on our allowable expenses guide to keep your tax bill fair.

This article is general information, not financial advice or tax advice. Figures use 2026/27 UK rates. MTD ITSA thresholds and timings are being phased in — confirm current rules on gov.uk or with an accountant.