- Your salary stays taxed through PAYE when you run a business on the side.
- Sole traders must register for Self Assessment once trading income tops £1,000.
- Sole trader profits pay Class 4 National Insurance at 6%, then 2% above £50,270.
Your tax obligations when running a business while employed come down to this: your salary stays taxed through PAYE, and as a sole trader you report business profits on a Self Assessment tax return once trading income passes £1,000 a year. A sole trader accountant can handle that return for you. This guide covers what you owe and when to file it.
What are your tax obligations when running a business while employed?
Running a business while working full time means dealing with three taxes: Income Tax, Corporation Tax if you set up a company, and National Insurance. Getting them wrong leads to penalties, so it’s worth knowing which apply to you before your first tax year ends.
If you’re still deciding whether you can be employed and self-employed at the same time, start there. This section covers what you owe and what you file once you are.
Income Tax
Your employer keeps taxing your salary through PAYE, so nothing changes there. As a sole trader, you need to register for Self Assessment once your gross trading income passes £1,000 a year, the limit of the trading allowance.
If you run a limited company and pay yourself a salary, it goes through the company’s own payroll. HMRC gives you a second tax code for it, usually BR because your job already uses your personal allowance, as explained in our guide to tax on a second job.
Your return needs to show all your income for the year, including your salary and benefits as well as your business profits. Paper returns are due by 31 October and online returns by 31 January after the tax year ends, so keep those dates in mind when submitting your Self Assessment tax return.
Corporation Tax
If you set up a limited company, the company pays Corporation Tax on its profits. You need to register for Corporation Tax within three months of the company starting to do business.
The company files a Company Tax Return each year, plus VAT returns if it’s VAT-registered. You personally pay Income Tax on any salary and dividends you take, and registering properly with HMRC and Companies House helps you avoid penalties.
National Insurance
Your employer deducts Class 1 National Insurance from your salary through PAYE, as usual. As a sole trader, you also pay Class 4 National Insurance on your profits through Self Assessment: 6% between £12,570 and £50,270, and 2% above that.
Class 2 National Insurance is no longer compulsory, though you can pay it voluntarily if your profits are below £7,105 to protect your State Pension record. If you run a limited company instead, the salary it pays you goes through its payroll, so Class 1 applies to that pay once it passes the threshold.
Does your employment contract limit your side business?
Your contract matters as much as your tax position when you start a business alongside a job. It can include disclosure requirements and intellectual property clauses that affect what you can do.
Legal restrictions and disclosure requirements
Before you start trading, read your employment contract and check your business idea doesn’t breach any disclosure agreement or intellectual property terms. Most contracts ask you to tell your employer if you take on a second job, and that usually includes running your own business.
Being open with your employer helps you avoid conflicts later. Tell them what you’re planning and get approval if your contract requires it.
Intellectual property
Don’t use your employer’s resources or confidential information in your new business, as that can lead to legal disputes. Keep your own work, research and ideas clearly separate from your job, so you can show they were developed independently.
Should you register as a sole trader or a limited company?
One of the first decisions is whether to trade as a sole trader or set up a limited company. Each affects what you pay and file, and our guide to sole trader vs limited company tax compares the two in detail.
Setting up a limited company
A limited company means registration with Companies House, appointing a director and filing annual accounts. The company pays Corporation Tax on its profits.
Setting up a company can also clash with your employment contract. Check it doesn’t breach any restrictions or disclosure requirements before you register.
Operating as a sole trader
As a sole trader, you register with HMRC and file a Self Assessment tax return each year. You pay Income Tax and Class 4 National Insurance on your business profits.
Trading as a sole trader is simpler to run, with lighter accounting and fewer filings. Weigh up both options against your income, your plans for the business and your contract.
How do you manage business finances alongside a full-time job?
Running a business while working full time leaves you with less time for admin, so it pays to keep your finances organised from the start.
Working with an accountant
Working with an accountant can help you:
- Save time on bookkeeping and returns
- Stay within the tax rules
- Claim every relief you’re entitled to
- Spot where the business can grow
That support is useful whether you’re a sole trader or run a limited company.
Using financial management tools
Accounting software automates manual tasks, keeps your records in one place and shows how the business is performing. Popular tools for small businesses include:
- QuickBooks
- FreshBooks
- Sage Accounting
- Xero
- FreeAgent
Want an accountant to handle this?
If your side business barely clears the trading allowance, filing your own Self Assessment is manageable. Once it’s growing, the questions get harder, such as which expenses you can claim and whether a limited company would save you tax.
Sleek’s Sole Trader Accountant service gives you a dedicated accountant who keeps your books, prepares your year-end accounts and files your Self Assessment tax return, with your salary and business profits on one return. AI handles the bookkeeping, a qualified accountant checks every figure, and you can see what was filed. If you’ve already set up a company, a limited company accountant covers the company side instead.
How can pensions and ISAs help you save tax?
Pensions and tax-free savings matter more when you’ve got two sources of income. Used well, they reduce your tax bill now or shelter what you earn later.
Tax relief on pension contributions
You get tax relief on private pension contributions up to 100% of your UK earnings, within an annual allowance of £60,000 that includes any employer contributions. Your business profits count as earnings, so a side business can raise how much you’re able to pay in with relief.
This applies whether you’re a sole trader or a limited company owner, so it’s worth reviewing your contributions each year.
ISAs and other savings
ISAs let you save or invest without paying tax on the interest or returns. Using them alongside your pension helps you build savings from both your salary and your business without adding to your tax bill.
How Sleek helps with tax when you run a business while employed
Running a business while working full time means two systems at once: PAYE on your salary and Self Assessment on your business profits. Getting the registration, deadlines and National Insurance right in your first year saves you a surprise bill in January.
Sleek’s accountants take care of the business side, from bookkeeping to filing your Self Assessment tax return, so you can keep your job and grow the business. For quick answers in the meantime, see our tax FAQs.
Sleek handles your tax while you run a business and a job
A dedicated accountant keeps your books and files your Self Assessment alongside your PAYE salary.
FAQs on tax obligations when running a business while employed
Can my accountant do this for me?
Yes. An accountant can register you for Self Assessment, keep your business records and file your return, with your PAYE salary and business profits on the same return. You’ll still need to share your P60 and business figures, but you won’t have to work out the tax yourself. Sleek does this through its Sole Trader Accountant service.
Will my side business push me into a higher tax band?
It can. Your business profits are added to your salary, so if your job already uses your personal allowance, every pound of profit is taxed at your marginal rate. In England, Wales and Northern Ireland, income above £50,270 is taxed at the 40% higher rate, and Scotland has its own bands.
Can I pay tax on my business profits through my PAYE tax code?
Yes, if you owe less than £3,000, already pay tax through PAYE and file your return online by 30 December, or on paper by 31 October. HMRC then collects the bill in 12 monthly instalments from your salary instead of one payment in January. You can’t use it if you owe £3,000 or more, even if you pay part of the bill first.
Does Making Tax Digital apply if I also have a job?
Only if your self-employment and property income is high enough. Making Tax Digital for Income Tax applies from 6 April 2026 when that gross income is over £50,000, falling to £30,000 from April 2027, and your salary doesn’t count towards either figure. If it applies, you’ll keep digital records and send quarterly updates through compatible software.
