When Should You Register a Limited Company in the UK? 2025 Guide

Many self-employed people start as sole traders because it is quick, simple, and free. You register with HMRC for self-assessment, keep records of your income and expenses, and pay income tax and National Insurance through your annual tax return. As business grows, the question of whether to convert to a limited company becomes increasingly relevant, but the right time to make that switch is not always obvious because it depends on your profit level, your plans for reinvesting, and factors beyond pure tax efficiency.

This guide explains when registering a limited company makes financial sense in the UK for 2025, what the practical steps look like, and what ongoing costs you need to account for when comparing the two structures. Use our sole trader vs limited company calculator to compare the tax position at your current profit level.

How sole trader tax works in 2025/26

As a sole trader you pay income tax on your taxable profits at the same rates as an employee: 20% on profits between £12,570 and £50,270, 40% on profits between £50,271 and £125,140, and 45% on profits above £125,140. You also pay Class 4 National Insurance at 6% on profits between £12,570 and £50,270, and 2% above that. Additionally you pay Class 2 NI at £3.45 per week to maintain state pension entitlement, though this is being absorbed into Class 4 from 2025/26.

The combined income tax and Class 4 NI rate for a sole trader with profits in the basic rate band is therefore 26% between £12,570 and £50,270. In the higher rate band it is 42%. These rates apply to all your profits regardless of whether you actually draw them out or reinvest them in the business. You pay tax on profit earned, not on what you take home.

How limited company tax works differently

A limited company pays corporation tax on its profits at 25% for profits above £250,000 or 19% for profits below £50,000, with marginal relief between those levels. The company is a separate legal entity, and you only pay personal tax on money you extract from it as salary or dividends. Profits left in the company are taxed only at corporation tax rates, not at income tax rates.

This creates the fundamental opportunity for tax deferral. If you only need to draw £40,000 from your business to live comfortably but your business generates £80,000 profit, as a sole trader you pay income tax and NI on all £80,000. As a limited company director, you pay corporation tax on £80,000 at the company level, but you only pay personal tax on the £40,000 you extract. The remaining £40,000 stays in the company and can be reinvested, saved, or extracted in a future year at a time of your choosing.

The break-even profit level

The point at which incorporating generally saves you money depends on how much profit you need to draw from the business each year. If you consistently need to extract all your profits to fund your lifestyle, the tax saving from incorporation is smaller because most of the money passes through to personal level anyway. If you can afford to leave some profit in the company, the saving grows with each pound left behind.

Most accountants suggest that the tax saving becomes meaningful enough to justify the additional administration once your profits reach approximately £40,000 to £50,000 per year, assuming you can retain some profit in the company. Below that level, the cost of an accountant to run the company, Companies House filing fees, and the additional complexity may exceed the tax saving, particularly if you are still spending a lot of time building the business.

Limited liability protection as a non-tax reason

Tax efficiency is not the only reason to incorporate. Limited liability is the other major consideration. As a sole trader you have unlimited personal liability for business debts. If your business fails or faces a legal claim that exceeds its assets, your personal assets including your home can be at risk. A limited company separates your personal and business finances, and in most circumstances limits your exposure to the value of your shares in the company.

For businesses with meaningful contracts, client relationships that carry risk, or employees, limited liability becomes more important irrespective of the profit level. A sole trader web developer who builds websites might have minimal liability. A sole trader contractor doing safety-critical work, a business that holds customer data, or anyone who employs staff has meaningfully more risk exposure that the limited liability structure helps to manage.

The practical steps to incorporate

Registering a limited company at Companies House takes less than 24 hours online and costs £50 using the standard web incorporation service. You choose a company name, confirm the registered office address, provide details of directors and shareholders, and pay the filing fee. The company exists from the date of incorporation and you can open a business bank account and start invoicing as the company immediately.

Converting an existing sole trader business to a limited company involves transferring business assets and contracts to the new entity. This does not happen automatically on incorporation. Any existing contracts with clients need to be assigned to or novated into the new company. Bank accounts need to be updated. HMRC registration for corporation tax and PAYE needs to be completed. Your sole trader self-assessment registration does not automatically end and needs to be formally closed once your final sole trader tax return is filed.

Ongoing costs of a limited company

Running a limited company has costs that do not exist for sole traders. You need a business bank account, which typically costs £5 to £15 per month. Annual accounts must be filed at Companies House and with HMRC, which requires an accountant unless you are confident preparing them yourself. A typical accountant fee for a small contractor company is £1,000 to £2,500 per year. The confirmation statement costs £34 per year to file at Companies House. PAYE registration and running adds a small overhead if you take a salary.

These costs need to be set against the tax saving to assess whether incorporation makes financial sense at your current income level. If the total additional cost of running a limited company is £2,000 per year and the tax saving at your profit level is £4,000, incorporation saves you £2,000 net. If those numbers are reversed, staying as a sole trader is financially rational even if the limited company would technically produce a lower tax bill in isolation.

Pension contributions as a tax planning tool

Whether you operate as a sole trader or a limited company, pension contributions are one of the most tax-efficient ways to reduce your taxable profit. Limited company directors who make employer pension contributions reduce the company's taxable profits at the corporation tax rate and suffer no income tax or NI on the contribution. Sole traders who make personal pension contributions receive income tax relief at their marginal rate. Both structures benefit significantly from pension planning, particularly as profits approach and exceed the higher rate threshold. Our UK salary calculator includes pension contributions in its take-home pay modelling so you can see how contributions affect your net income.