The sole trader vs limited company tax calculator has become many people’s first stop when they start thinking about incorporation. Type in your annual profits, hit calculate, and a figure appears showing how much more you could take home as a limited company director. It’s satisfying and, at a high level, reasonably accurate.

The problem is that most people treat the output as a decision rather than a starting point. The calculator compares structures at a single profit figure. It can’t account for your dividend tax position, your plans for retained profits, your IR35 exposure, your tolerance for additional admin, or any of the dozen other factors that determine whether incorporation actually benefits you in practice.

We use these calculators ourselves when talking through the structure question with clients. They’re genuinely useful as a conversation opener. But in our experience, the decision to incorporate is rarely as straightforward as the headline saving suggests — and sometimes the right answer is to stay as a sole trader for longer than you might expect.

A good sole trader vs limited company tax calculator for 2026/27 will compare your total tax burden under both structures at the same profit level. On the sole trader side, it applies Income Tax at 20% on profits between £12,570 and £50,270, rising to 40% on profits between £50,271 and £125,140, and 45% above that. It also applies Class 4 National Insurance Contributions at 6% on profits between £12,570 and £50,270, and 2% on anything above, plus Class 2 NIC of £3.45 per week if profits exceed the lower profits threshold.

On the limited company side, the calculator models the standard approach: paying yourself a salary up to the personal allowance of £12,570 (avoiding National Insurance on the salary portion), then extracting remaining profits as dividends. Corporation Tax is applied at 19% on profits under £50,000, 25% on profits over £250,000, with marginal relief scaling between those figures. Dividends then attract Dividend Tax at 8.75% (basic rate), 33.75% (higher rate), or 39.35% (additional rate), after a £500 annual dividend allowance.

The saving this produces looks significant on paper — and at higher profit levels, it genuinely is. The calculator is doing its job correctly. The issue is what it leaves out.

Calculators model a clean extraction: you earn profit, you pay corporation tax, you take everything out as dividends. Real businesses rarely work that way.

If you intend to retain profits in the company — to reinvest, to build a buffer, or simply because you don’t need the cash yet — the tax comparison looks more favourable for the limited company, because you’re deferring the dividend tax. If, on the other hand, you need most of the profit for personal living expenses each month, you’ll be extracting nearly everything as dividends anyway, and the gap between structures narrows considerably.

There’s also the question of what counts as a deductible expense. A limited company has some additional flexibility here — certain costs that sit in a grey area for sole traders are more clearly allowable through a company. But this isn’t a blank cheque, and it shouldn’t be the primary reason to incorporate.

Then there are the costs the calculator ignores entirely: accountancy fees for year-end accounts and a Corporation Tax return tend to run higher than sole trader accounts, there’s a Confirmation Statement to file annually, and if you want to close the company one day, there are dissolution costs to consider. These aren’t huge figures, but they’re real ones that reduce the net saving the calculator displays.

A more honest comparison accounts for these running costs before celebrating the headline number.

This is the question we get most often, and there’s a reasonably consistent answer in our experience: once your profits push comfortably into the higher rate Income Tax band — roughly above £50,000 to £55,000 in sustained annual profits — the case for a limited company structure becomes genuinely compelling for most self-employed people.

Below that level, the saving after accounting for additional accountancy and filing costs is often modest enough that it doesn’t justify the added administrative overhead. Sole trader status is simpler, faster to maintain, and easier to wind down if your circumstances change.

Between around £35,000 and £50,000, the answer genuinely depends on your situation. If you plan to grow, if you want the credibility a limited company can offer with certain clients, or if you’re already using Xero and comfortable with the additional admin, incorporating sooner can make sense. But if you’re happy at your current scale and you need all of your profit each month, the tax saving at that level may not be worth the friction.

Above £80,000, the calculation shifts noticeably. The combined effect of higher-rate Income Tax and Class 4 NIC on sole trader profits at that level is significant, and the limited company structure — even after dividend tax — typically produces a meaningfully better outcome. This is where clients often come to us saying they wish they’d made the switch sooner.

If you work primarily for one or two clients, particularly in a contractor or consultancy capacity, the structure question can’t be separated from IR35 — the off-payroll working rules that determine whether HMRC treats your income as employment income regardless of how you’ve structured your business.

A calculator will show you a generous take-home figure as a limited company. But if your contracts fall inside IR35, that saving largely disappears. You’d be paying Employer’s and Employee’s National Insurance on your deemed salary, with none of the dividend extraction efficiency the calculator assumed.

This doesn’t mean you shouldn’t incorporate — it means you need to understand your IR35 position before making the structure decision. Working with a single end client, having little substitution right, and being fully integrated into the client’s business are the kind of indicators that put a contract at risk of an inside determination.

We review IR35 exposure as part of any incorporation conversation, because the tax comparison only makes sense once you know whether the limited company route is actually available to you in the way the calculator assumes. If you’re a contractor in IT or engineering — two sectors we work closely with — this step is non-negotiable before making any structural change.