You can legally freelance alongside a full-time job in the UK, as long as your employment contract allows it and you declare the income. If your freelance income is more than £1,000 in a tax year, you register for Self Assessment by 5 October after that tax year ends and pay Income Tax on your profit at your highest rate, because your salary has already used your Personal Allowance.
This guide covers the parts that are specific to doing it on top of a PAYE job: your contract, how the tax stacks on your salary, National Insurance, and keeping the workload sustainable. For general self-employment basics, see freelancing in the UK: a beginner's guide.
Check your employment contract first
Before you take on a client, read your contract and staff handbook for anything that limits outside work. Common clauses include:
- Outside work or exclusivity clauses: some require you to get permission before taking other work, or ban it outright for certain roles.
- Conflict of interest: working for a competitor, client or supplier of your employer is the most likely thing to cause trouble.
- Confidentiality: you cannot use your employer's information, contacts or materials in your freelance work.
- Intellectual property: some contracts claim ownership of work created using company time or equipment, so keep freelance work on your own devices and in your own time.
- Working time: employers have health and safety duties around rest and working hours, and some ask you to disclose other jobs for that reason.
When you need to tell HMRC
The trading allowance lets you earn up to £1,000 of gross trading income a year tax-free without telling HMRC. Above that, you must register for Self Assessment by 5 October after the end of the tax year in which you started. For freelance work started in the 2026/27 tax year (6 April 2026 to 5 April 2027), that means registering by 5 October 2027, filing online and paying by 31 January 2028.
Once registered, you can either claim the £1,000 trading allowance or deduct your actual business expenses, but not both. If your expenses are higher than £1,000, claiming expenses is usually better. Note that the allowance cannot be used for income from your own employer or your spouse's employer. HMRC's guidance on the trading allowance sets out the rules.
How the tax stacks on top of your salary
Your salary uses up your £12,570 Personal Allowance first, so every pound of freelance profit is taxed at your marginal rate: 20% up to £50,270 of total income, 40% above that and 45% over £125,140 (Scotland has different bands). Two examples for 2026/27 in England, Wales or Northern Ireland:
| Salary | Freelance profit | Extra Income Tax |
|---|---|---|
| £35,000 | £6,000 | £1,200 (all at 20%) |
| £48,000 | £8,000 | £2,746 (£2,270 at 20%, £5,730 at 40%) |
Watch the thresholds. Freelance profit that takes your total income over £50,270 is taxed at 40%, over £60,000 can trigger the High Income Child Benefit Charge, and over £100,000 starts to reduce your Personal Allowance. Making pension contributions can bring your adjusted income back down. Use the take-home pay calculator to see where your salary sits.
National Insurance on freelance profits
Class 4 National Insurance is worked out on your self-employed profits on their own, not added to your salary. That means many people with a modest side business pay no extra National Insurance at all.
| Annual freelance profit | National Insurance position (2026/27) |
|---|---|
| Under £7,105 | Nothing due; voluntary Class 2 optional |
| £7,105 to £12,570 | Nothing to pay; you are treated as having paid Class 2 |
| £12,570 to £50,270 | Class 4 at 6% on profit in this band |
| Over £50,270 | Class 4 at 2% on profit above this |
As an employee you are usually already building State Pension qualifying years through your job, so voluntary Class 2 is rarely needed if you have a full-time salary.
Paying the bill: payments on account and tax codes
The first Self Assessment bill can be a shock. If your bill is over £1,000 and less than 80% of your total tax is collected through PAYE, HMRC also asks for payments on account: two advance payments towards next year's bill, due on 31 January and 31 July. In your first year this can mean paying around one and a half years of freelance tax in one go.
If you owe less than £3,000 and file online by 30 December, you can ask HMRC to collect it through your PAYE tax code over the following year instead. Either way, the simplest habit is to move a set share of every invoice into a separate savings account the day you are paid: 20% to 25% if you are a basic rate taxpayer, and 40% to 45% if your freelance profit falls in the higher rate band. Interest on that pot counts towards your Personal Savings Allowance.
Making Tax Digital and record keeping
Making Tax Digital for Income Tax requires quarterly digital updates from sole traders and landlords whose qualifying income is over a threshold. Qualifying income is self-employment and property income before expenses; your PAYE salary does not count. The thresholds are over £50,000 (based on 2024/25, from 6 April 2026), over £30,000 (based on 2025/26, from April 2027) and over £20,000 (based on 2026/27, from April 2028). Most people freelancing on the side are below these for now, but keep digital records from the start: invoices, receipts, mileage and a simple spreadsheet or app.
Online platforms that pay you for services are also required to report seller income to HMRC, so assume HMRC can see platform earnings.
Keeping it sustainable
- Set fixed freelance hours and protect at least one full day off a week.
- Never use employer time, equipment or software licences for client work.
- Price for the tax: a £30 an hour job is worth about £24 to a basic rate taxpayer and £18 to a higher rate taxpayer.
- Build a small buffer for late-paying clients, separate from your tax pot. The emergency fund calculator helps size it.
- If you have a student loan, Self Assessment adds repayments on your combined income above your plan threshold. Check with the student loan calculator.
- Consider paying some profit into a pension: it gets tax relief and reduces adjusted income near the £60,000 and £100,000 thresholds.
Frequently asked questions
Can my employer stop me freelancing in my spare time?
Do I need to tell my employer about my side business?
How much can I earn freelancing before paying tax?
Will freelancing push me into the higher rate tax band?
Do I pay National Insurance on freelance income if I already pay it through my job?
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