Freelancing Alongside a Job: UK Rules to Know
Freelancing alongside a job is one of the safest ways to test a business idea in the UK: your salary pays the bills while you find clients. It also brings rules that many side hustlers miss, from clauses in your employment contract to registering with HMRC and paying tax on top of your PAYE income. This guide walks through what to check and what to do. It is general information, not tax or legal advice, and rates and thresholds change every tax year, so confirm the details on GOV.UK or with an accountant.
Key takeaways
- Read your employment contract first: look for clauses on outside work, conflicts of interest, confidentiality and intellectual property.
- If your gross freelance income is £1,000 or less in a tax year, the trading allowance may mean you do not need to tell HMRC (there are exceptions).
- Above £1,000, register for Self Assessment by 5 October after the end of the tax year you started.
- Your salary usually uses up your Personal Allowance, so freelance profit is often taxed from the first pound at your marginal rate.
- Set aside tax from every client payment, because nothing is deducted automatically.
Plenty of people in the UK earn some money on the side: a designer taking a few logo projects, a developer building websites at weekends, a teacher tutoring in the evenings. As soon as you sell your services to clients for profit, you are usually self-employed for that work, even if you are an employee for your main job. You can be both at the same time, and HMRC treats the two kinds of income differently.
Check your employment contract first
Before you take on a single client, reread your employment contract and staff handbook. Nothing in UK law stops most employees from doing other work, but your contract can set conditions, and breaking them could put your job at risk.
Clauses to look for
- Outside work or "moonlighting" clauses. Some contracts require you to ask permission before taking other work, or ban work for competitors.
- Conflict of interest. Working for your employer's clients, suppliers or competitors is the most common problem.
- Confidentiality. You cannot use your employer's information, client lists or methods in your freelance work.
- Intellectual property. Some contracts claim ownership of work created during employment, sometimes even outside working hours if it relates to the employer's business.
- Working time and exclusivity. Some roles, especially in regulated or senior positions, restrict other paid work altogether.
Pro tip
If anything is unclear, ask HR or your manager in writing and keep the reply. A short email saying "I plan to do some freelance copywriting for small businesses outside working hours, using my own equipment, with no overlap with our clients" is usually enough to start the conversation. If the stakes are high, an employment law adviser can review the contract.
Keep the two worlds separate
Even where side work is allowed, do it on your own time and with your own equipment. Do not answer client emails during work hours, use a work laptop for freelance projects or approach colleagues and contacts from your job for freelance work without checking first. Clean separation protects your job and your ownership of the work.
Do you need to tell HMRC at all?
The answer depends mainly on how much you earn from your freelance work. Here the key figure is the trading allowance.
The figure is based on gross income, meaning what clients pay you before any costs. How it works:
- £1,000 or less of gross trading income: this is "full relief". You may not need to tell HMRC or pay tax on it, although there are exceptions, so check GOV.UK if your situation is unusual.
- More than £1,000: you must register for Self Assessment. When you work out your profit, you can either deduct your actual allowable expenses or deduct the £1,000 allowance instead ("partial relief"). You cannot claim both.
- Expenses above £1,000: claiming actual expenses is usually the better option.
The tax year runs from 6 April to 5 April, and the current one is 6 April 2026 to 5 April 2027. The £1,000 limit applies to each tax year, not to each client. There is also a separate £1,000 property allowance for things like renting out a driveway, which does not count toward the trading allowance.
Common mistake
Assuming that a small amount of profit means you do not need to register. The £1,000 test looks at gross income, not profit. If clients paid you £1,800 and your costs were £900, your profit is £900, but your gross income is over £1,000, so you need to register.
How to register as self-employed
You can start trading straight away; you do not need permission from HMRC to take on your first client. If you earn more than £1,000 from self-employment in a tax year, you register for Self Assessment as a sole trader through GOV.UK.
- Note your start date. This is roughly when you started trading, such as your first paid project or when you began advertising your services.
- Register online on GOV.UK. You will need your National Insurance number and basic details about the business. If you already file Self Assessment for another reason, you add self-employment to your existing record rather than registering from scratch.
- Meet the deadline. Register by 5 October after the end of the tax year in which you started. If you started freelancing in June 2026, that tax year ends on 5 April 2027, so you would register by 5 October 2027.
- Wait for your reference. HMRC sends you a Unique Taxpayer Reference, which you use to file your return.
Registering late and not paying your tax by 31 January can lead to a "failure to notify" penalty, so put the 5 October date in your calendar as soon as you pass £1,000. You do not need to tell your employer's payroll anything about this; Self Assessment is separate from PAYE.
How side income is taxed on top of your salary
This is the part that surprises most people with a job. Your salary is taxed first through PAYE, and it usually uses up your Personal Allowance. Your freelance profit is then added on top of your salary, so it is taxed at whatever band your combined income reaches.
Income Tax bands for 2026/27
| Band | Taxable income | Rate |
|---|---|---|
| Personal Allowance | Up to £12,570 | 0% |
| Basic rate | £12,571 to £50,270 | 20% |
| Higher rate | £50,271 to £125,140 | 40% |
| Additional rate | Over £125,140 | 45% |
These bands apply in England, Wales and Northern Ireland. Scotland has different Income Tax bands, so check the Scottish rates on GOV.UK if you live there. The Personal Allowance also falls by £1 for every £2 of adjusted net income over £100,000.
National Insurance on freelance profit
National Insurance works differently. Your employer deducts employee National Insurance from your salary. For self-employment, Class 4 National Insurance is charged on your self-employed profits: 6% on profits between £12,570 and £50,270 and 2% above that, for 2026/27. If your freelance profit is below £12,570, you would normally pay no Class 4 at all, even with a full-time salary.
Class 2 National Insurance is treated as paid if your profits are £7,105 or more. With lower profits you can choose to pay voluntary Class 2, but if you already pay National Insurance through your job you may not need it to protect your record. Check your National Insurance record on GOV.UK if you are unsure.
Example (simplified)
Imagine Sam earns a salary of £40,000 in England and does freelance illustration on the side. In the 2026/27 tax year clients pay Sam £5,000, and Sam's costs are only £300, so Sam deducts the £1,000 trading allowance instead, leaving a profit of £4,000.
Sam's total income is £44,000, which stays inside the basic rate band, so the whole £4,000 is taxed at 20%: £800 of Income Tax. The profit is below £12,570, so there is no Class 4 National Insurance. Sam's Self Assessment bill is about £800.
Now imagine the salary is £48,000 and the freelance profit is £8,000. The first £2,270 of profit is taxed at 20% (£454) and the remaining £5,730 at 40% (£2,292), so the bill is about £2,746. This is simplified: it ignores other income, pension contributions, student loans, Scotland and any changes to your tax code.
The lesson: if your salary is close to the higher rate threshold, a good chunk of your side income could be taxed at 40%. Work out where your salary sits before you decide how much to save.
Payments on account and other extras
Once your Self Assessment bill reaches £1,000 or more, HMRC normally asks for payments on account: two advance payments toward next year's bill, each normally half of last year's bill, due 31 January and 31 July. People with a job are often exempt, because payments on account are not required if more than 80% of your tax was already paid at source, such as through PAYE. As your side business grows, that exemption can disappear, and your January bill can suddenly jump. If you have a student loan, repayments on your freelance income are also calculated through Self Assessment and paid with the 31 January balancing payment.
Records, expenses and a separate account
Even a small side business needs basic records: every invoice, every payment received and receipts for any costs you claim. Keep them for each tax year so you can complete your return in January without a scramble.
- Use a separate bank account. Sole traders are not legally required to have one, but keeping freelance money apart from your salary makes records and tax saving far easier.
- Claim only business costs. Allowable expenses must be wholly and exclusively for the business. For mixed items like a phone or broadband, claim only the business share.
- Use simplified expenses where they help. If you work from home for 25 hours or more a month on your freelance work, you can use a flat monthly rate instead of working out a share of household bills.
- Keep it on the cash basis. Cash basis is the default for sole traders, so you record income when it arrives and expenses when you pay them.
Keep an eye on Making Tax Digital for Income Tax as you grow. It applies from 6 April 2026 to sole traders and landlords with qualifying income over £50,000, falling to over £30,000 from April 2027 and over £20,000 from April 2028. Qualifying income is based on gross self-employment and property income, not your salary, so most side businesses are not affected at first.
Managing time, energy and risk
The tax side is manageable. The harder part for most people is fitting client work around a full-time job without burning out or letting either side down.
- Set fixed freelance hours. For example, two evenings a week and Saturday mornings. Quote deadlines that fit those hours, not your optimistic best case.
- Tell clients your availability. Clients cope well with "I reply within one working day" and badly with silence.
- Think about cover. Your employer's insurance does not cover your freelance work. Depending on what you do, consider public liability or professional indemnity insurance.
- Watch your data. If you handle client contact details or other personal data, UK GDPR applies to you as a sole trader too.
Your side hustle setup checklist
- Reread your contract and handbook for outside work, IP and confidentiality clauses
- Get written approval from your employer if your contract requires it
- Track gross freelance income from the first payment
- Register for Self Assessment by 5 October once you pass £1,000 in a tax year
- Open a separate account for freelance money
- Move a share of every payment into a tax savings pot, based on your salary band
- Set fixed freelance hours and protect some of your annual leave
Frequently asked questions
Do I have to tell my employer I am freelancing?
It depends on your contract. Some contracts require permission for any outside work, others only restrict work for competitors, and some say nothing. Even if you are not required to, being open about non-competing work often avoids misunderstandings later.
I earned under £1,000 but had big costs. Should I still register?
If your expenses are higher than your income, you may want to register so you can report a loss, which can sometimes be used against other income. That is a decision worth checking with an accountant, as the rules on using losses have conditions.
Should I set up a limited company for my side business?
Most side businesses start as sole traders because it is simpler and cheaper to run. A limited company brings extra admin, such as annual accounts and a confirmation statement, and usually only makes sense once profits are higher or you need limited liability.
Related reading
The bottom line
Freelancing alongside a job is a smart way to build a business with less risk, as long as you get the basics right. Clear it with your contract, track your gross income against the £1,000 trading allowance, register for Self Assessment by 5 October when you need to and save for tax at the rate your combined income reaches.
Rates, bands and thresholds change every tax year, and Scotland has its own Income Tax bands. Treat this as general information, check the current figures on GOV.UK or with HMRC, and ask an accountant if your situation is not straightforward.
