Your evening and weekend project is paying real money now. Maybe it is matching your day job. The question stops being "is this fun?" and becomes "can I do this properly, and what does HMRC expect when I do?"
This is the roadmap. We cover when you must register, how to choose between staying a sole trader and forming a limited company, the tax you will actually pay, the VAT line you need to watch, and the deadlines that catch people out in their first full year.
It is written for UK side hustlers and early-stage founders going full-time. All figures are for the 2025/26 tax year and link to the gov.uk source. If you would rather hand the admin to someone, we explain where Zmartly fits at the end.
When does a side hustle become a business HMRC cares about?
There is a clear line, and it is not about quitting your job. It is about income.
You get a tax-free trading allowance of up to £1,000 of gross trading income each tax year. If your side hustle brings in £1,000 or less in a tax year, you usually do not need to tell HMRC at all (gov.uk trading allowance).
The moment your gross trading income for a tax year goes over £1,000, that changes. You must register for Self Assessment and declare the income. Most people scaling a side hustle cross that line quickly.
"Gross" matters here. It is your turnover before expenses, not your profit. So you can owe a registration duty even on a venture that is barely breaking even.
One more point that trips people up: you can be employed and self-employed at the same time. Going "full-time" on your hustle is your decision, not HMRC's. The registration trigger is the £1,000, whether you have a day job or not.
What is the registration roadmap, step by step?
Here is the order to do things in once you have crossed the £1,000 line or decided to go full-time.
Step 1. Register with HMRC for Self Assessment. If your gross income for a tax year is more than £1,000, you must register by 5 October in the following tax year (gov.uk). For example, if you cross the line during 2025/26 (the year ending 5 April 2026), the deadline to register is 5 October 2026. Do not leave it to the last week. Registration produces a Unique Taxpayer Reference that arrives by post.
Step 2. Decide your structure. Sole trader or limited company. This is the big one, so it has its own section below.
Step 3. If you choose a limited company, register it at Companies House. You can do this online for £100, and the company is usually registered within 24 hours (gov.uk company formation). A company is a separate legal person, so it brings its own filing and tax obligations.
Step 4. Set up your money and records from day one. A separate business bank account, a simple bookkeeping system, and a folder for receipts. You are legally required to keep records of your income and expenses. Getting this right early saves a painful clean-up later.
Step 5. Watch the thresholds as you grow. VAT registration and, from April 2026, Making Tax Digital for Income Tax both kick in at set income levels. We cover both below so you are not caught out.
Our services for sole traders and startups walk new businesses through exactly this sequence.
Should I stay a sole trader or set up a limited company?
There is no single right answer. It depends on your profit level, your appetite for admin, and whether you need limited liability or outside investment.
Here is the honest comparison.
| Factor | Sole trader | Limited company |
|---|---|---|
| Set-up | Register for Self Assessment with HMRC | Register at Companies House (£100 online) plus HMRC |
| Legal status | You and the business are the same | A separate legal person |
| Liability | You are personally liable for debts | Generally limited to what you put in (with exceptions) |
| Profits taxed via | Income Tax and Class 4 NIC on profits | Corporation Tax, then you pay tax on salary or dividends taken |
| Public filing | Your accounts stay private | Accounts and details filed publicly at Companies House |
| Admin load | Lighter | Heavier (annual accounts, confirmation statement, payroll if you take a salary) |
In practice, the mistake we most often see is incorporating too early purely "for the tax", before profits are high enough to make the extra admin and filing worth it. The flip side is also real: stay a sole trader too long and you carry unlimited personal liability on a business that has outgrown it.
A rough rule of thumb many accountants use is to revisit the question seriously once profits are consistently into the higher-rate territory, but the right trigger for you depends on liability, clients, and plans for investment. It is exactly the kind of decision worth a short conversation rather than a guess.
If you do incorporate, there is ongoing company housekeeping to manage, from the confirmation statement to filing deadlines. That is what our company secretarial service is for.
How much tax will I pay as a full-time sole trader?
As a sole trader you pay Income Tax and Class 4 National Insurance on your profits (turnover minus allowable expenses), reported through Self Assessment.
For 2025/26 the building blocks are:
| Item | 2025/26 figure |
|---|---|
| Personal Allowance (tax-free) | £12,570 |
| Income Tax basic rate | 20% |
| Income Tax higher rate (from £50,271) | 40% |
| Class 4 NIC main rate (profits £12,570 to £50,270) | 6% |
| Class 4 NIC additional rate (profits above £50,270) | 2% |
Sources: Income Tax rates, Income Tax allowances and self-employed NIC rates.
Illustrative example: Priya goes full-time
Priya is a freelance graphic designer who has gone full-time on her hustle. In 2025/26 her business profit (after allowable expenses) is £40,000. She has no other income. The figures below use 2025/26 rates.
Income Tax
- Personal Allowance: £12,570 is tax-free.
- Taxable income: £40,000 minus £12,570 = £27,430.
- All of it falls in the basic rate band, taxed at 20%: £27,430 x 20% = £5,486.
Class 4 National Insurance
- Profits between £12,570 and £40,000 are charged at 6%.
- £40,000 minus £12,570 = £27,430, taxed at 6% = £1,645.80.
Priya's total for the year
- Income Tax £5,486 plus Class 4 NIC £1,645.80 = £7,131.80.
That leaves her with £32,868.20 after Income Tax and Class 4 NIC on £40,000 of profit. Note that part of this bill can fall due as payments on account towards the following year, which we cover under deadlines below. To model your own numbers, try our self-employed tax calculator.
This example ignores reliefs such as pension contributions and assumes England, Wales or Northern Ireland. Scotland sets its own Income Tax bands, so the Income Tax figures would differ there.
When do I need to register for VAT?
VAT is the threshold most growing businesses hit first, and it is based on turnover, not profit.
You must register for VAT once your VAT-taxable turnover goes over £90,000 in any rolling 12-month period, or if you expect to go over it in the next 30 days alone (gov.uk VAT registration thresholds). The standard VAT rate is 20% (gov.uk VAT rates).
"Rolling 12 months" catches people out. It is not your accounting year or the tax year. You check the total of the last 12 months at the end of every month, so a strong run of sales can tip you over mid-year.
Once registered, you charge VAT on your sales, reclaim VAT on eligible costs, and file VAT returns digitally under Making Tax Digital for VAT. If you sell mainly to consumers, adding 20% can feel like a price rise, so it is worth planning for the threshold before you reach it rather than after.
What are the key deadlines in my first full year?
Self Assessment runs on a fixed annual cycle. For a tax year that ends on 5 April, the dates are:
| Deadline | Date |
|---|---|
| Register for Self Assessment | 5 October after the tax year ends |
| Paper tax return | Midnight 31 October after the tax year ends |
| Online tax return | Midnight 31 January after the tax year ends |
| Pay the tax you owe (balancing payment) | Midnight 31 January after the tax year ends |
| Payments on account | 31 January and 31 July |
Source: gov.uk Self Assessment deadlines.
Two things surprise first-timers. The first is payments on account: HMRC often asks you to pay towards next year's bill in two instalments, on 31 January and 31 July, which can make your first January payment larger than expected. The second is Making Tax Digital for Income Tax. From 6 April 2026, sole traders and landlords with qualifying income over £50,000 (based on the 2024/25 tax year) must keep digital records and file quarterly updates (gov.uk MTD for Income Tax). Lower income thresholds follow in later years, so it is worth getting your bookkeeping digital now.
Missing a filing or payment deadline triggers penalties and interest, so put these dates in your calendar the day you register. If you would rather not track them at all, our Self Assessment service handles registration, the return, and the deadlines for you.
Frequently asked questions
Do I need to register if my side hustle earns under £1,000?
Usually no. If your gross trading income is £1,000 or less in a tax year, the trading allowance means you typically do not need to tell HMRC. Once you go over £1,000 gross in a tax year, you must register for Self Assessment by 5 October in the following tax year.
Can I be employed and run a business at the same time?
Yes. Many people start a side hustle while employed. You pay tax through PAYE on your job and report your self-employed profits through Self Assessment. Going full-time is your choice, but the registration trigger is the £1,000 of gross trading income, not whether you have left your job.
Is a limited company always more tax-efficient than being a sole trader?
No. A company can be more efficient at higher profit levels, but it brings extra costs and admin: Companies House filing, annual accounts, a confirmation statement, and often payroll. At lower profits the savings may not cover the extra work. The right answer depends on your profit, liability needs, and plans, so it is worth getting tailored advice.
When do I have to register for VAT?
You must register once your VAT-taxable turnover goes over £90,000 in any rolling 12-month period, or if you expect to exceed it in the next 30 days. It is based on turnover, not profit, so a busy stretch can take you over even on thin margins.
How much does it cost to set up a limited company?
You can register a private limited company online with Companies House for £100, and it is usually registered within 24 hours. That is the formation fee only. Running a company brings ongoing costs such as annual accounts and a confirmation statement.
Get help with your tax return →
Ready to make it official?
Turning a side hustle into a full-time business is mostly about getting the foundations right: registering on time, choosing the structure that fits, and staying ahead of VAT and Self Assessment deadlines.
If you want that handled properly from day one, book a free call with a Zmartly accountant. We will register you, set up your records, and tell you straight whether sole trader or limited company is right for your numbers. Talk to us through our Self Assessment service.
