A calculator is only as honest as the figures you feed it. Most people feed it the wrong one.

Turnover is the wrong starting point. Two businesses invoicing £180,000 can land in completely different places once costs are in. The comparison runs on profit and on drawings.

Using a sole trader vs limited company calculator properly

Before you open any tool, have these to hand:

• Annual profit, meaning income after allowable business costs, not money in the bank.
• What you need to live on, month by month, after tax.
• What you would leave in the business if you had the choice.
• Other personal income, such as rent, a salary elsewhere, or a pension.
• Whether you are VAT registered, and on which scheme.

That third item does most of the work. A company only saves tax on profit you do not extract. Draw every penny each year and the advantage narrows sharply, because the money is taxed twice on the way out.

The fourth item catches people out too. Dividend income sits on top of your other income. A spouse with a salary, or a landlord with rental profit, can find the dividends taxed at a higher rate than the calculator assumed.

If a tool asks only for turnover and gives you a headline saving, close it. It has guessed at your costs and assumed you extract everything, and those two guesses are where the real answer lives.

Here is the mechanism, stripped back, for the 2026 to 2027 tax year.

As a sole trader, business profit is your income. It goes on your self assessment return and is taxed at the usual rates, rising to 45% at the top, with Class 4 National Insurance on top. There is no second layer. What the business makes, you are taxed on, whether you spend it or not.

A company is taxed separately. Corporation tax is 19% on profits up to £50,000 and 25% on profits above £250,000, with marginal relief in between, which produces an effective rate higher than 19% across that middle band. You can check the current rates on GOV.UK.

Notice the third row. That is the real lever. A business retaining profit to fund equipment, staff, or a quiet quarter is better served by the company rates. A business where every pound comes straight out has a much thinner case.

The Association of Taxation Technicians has pointed out that the tax advantage of incorporating has been eroded over recent years. There is no longer a profit figure at which the answer is automatic.

Every free tool models the tax and stops. These are the items that change the decision and never appear on screen.

Access to your own money

As a sole trader you draw when you like. As a director you cannot. Dividends can only be paid out of retained profit, and they need to be declared and documented. Owners who keep taking money regardless end up with an overdrawn director’s loan account and a tax charge on it.

The cost of running a company

Statutory accounts, a corporation tax return, a confirmation statement, payroll for the director, and your own self assessment. That is a bigger annual job than one tax return, and the fees reflect it. Set the saving against the running cost, not against zero.

Your first year in the company

The switch year is messy. You will have a final sole trader return and a first company period. Payments on account for the old trade often still fall due after the trade has stopped. Cash flow in that year rarely looks like either model.

Everything that is not tax

• Contracts, agency terms, and licences that name you personally.
• Insurance and any trade accreditation held in your own name.
• CIS gross payment status, if you are in construction.
• Mortgage lending, where two years of company accounts can reset the clock.
• Company accounts appearing on the public register at Companies House.

None of that shows up as a number. All of it decides whether the switch is worth the disruption this year or next.

Since 6 April 2026, sole traders and landlords with qualifying income above £50,000 keep digital records and send HMRC quarterly updates of income and expenses.

The updates are summaries, not extra tax returns. The annual return still has to be filed by the following 31 January. For the first group, the 2026 to 2027 return is due by 31 January 2028, with quarterly updates falling due on 7 August, 7 November, 7 February, and 7 May. HMRC has confirmed no late submission penalty points for that first group during the opening twelve months. After that, points accrue per late update, and a £200 penalty applies once four points are reached. Details sit on GOV.UK.

The thresholds drop over time. Qualifying income above £30,000 is brought in from April 2027, and above £20,000 from April 2028.

Does this make a company more attractive

Companies sit outside Making Tax Digital for Income Tax at the moment. That fact has been doing a lot of work in advertising this year, and a July 2026 survey of in-scope sole traders found roughly a quarter had already started forming a company partly because of the change.

Treat that as a survey estimate and a poor reason on its own. A company does not file fewer things. It files different things: statutory accounts, a corporation tax computation, a confirmation statement, and payroll submissions every month. If quarterly updates are the only thing pushing you, you are trading four light summaries for a heavier annual cycle.

Where the change does earn its place is as a prompt. If you were going to model the decision eventually, model it now, while you are setting up software anyway.

VAT is the part of incorporation that most often goes wrong, and no calculator mentions it.

Your VAT registration belongs to you as a sole trader. It does not follow the business into the company by default. Either the company registers in its own right, or the existing number is transferred using form VAT68. Both routes need doing before the first company invoice goes out, or you have invoices charging VAT under a number that no longer applies to the trade.

Incorporation is also the natural moment to check the scheme. Most people were put on standard VAT when they first registered and have never revisited it. Whether that is right depends on how much VAT you actually reclaim.

A procurement consultant came to me on the standard scheme. Box 4 on every return was close to empty, because his costs were overseas software and reverse charge services with no input VAT to recover. The set-up review moved him to the flat rate scheme. His VAT bill fell every quarter after that, on identical turnover.

The opposite case exists too. A trades business buying materials, plant, and fuel reclaims a lot, and the flat rate scheme would cost it money. The scheme has to follow your cost profile.

If you are incorporating and VAT registered, decide three things together: whether the number transfers, which scheme the company uses, and when the first return period starts. Decide them apart and you will spend the first quarter correcting things.

Most of this guide argues for caution. There are situations where the numbers are not close at all.

The clearest is a sole trader at £150,000 of turnover or more with genuine profit, who does not need to extract everything to live. At that level, profit is sitting in the additional rate territory, National Insurance applies to all of it, and the company rates plus a planned salary and dividend split produce a gap that pays for the extra compliance several times over.

Two more where the case is strong:

• Profit that funds growth. Vans, plant, a first hire, or a working capital buffer. Money retained in a company is taxed once at company rates. Money retained in a sole trade is taxed on you regardless.
• Customers who require it. Plenty of agencies, main contractors, and procurement functions will not engage a sole trader. That is not a tax argument, and it still settles the question.

Where the case is usually weak: profit under about £40,000 to £50,000, income that swings hard from year to year, or a business where every pound earned is spent by the end of the month. That £40,000 to £50,000 figure is a common rule of thumb rather than any official threshold, and it has moved as rates have changed.

The honest position is that a calculator gets you to a range. Your drawings, your other income, and your plans for the profit get you to an answer.