Setting up the second company took twenty minutes and cost fifty pounds. The new venture was different enough from the main trade to deserve its own name, we wanted it kept separate in case it failed, and a friend was coming in as a minority shareholder. Everything about the decision looked sensible, and most of it was.
The bit nobody mentioned, because we did not ask and the formation agent had no reason to, was what a second company does to the corporation tax rate the first one pays.
Two rates, and the band in between
Since April 2023 corporation tax has had two rates. Profits up to £50,000 are taxed at the small profits rate of 19%. Profits of £250,000 and above are taxed at the main rate of 25%. Between those two figures you pay the main rate less marginal relief, calculated using a fraction of 3/200, which works out as an effective 26.5% on every pound in the band.
That is the bit most owners half-know. The bit that catches people is the next sentence in the legislation: both the £50,000 and the £250,000 limits are divided by the number of associated companies.
The arithmetic that landed on us
Our trading company made £70,000 that year. On its own, the calculation runs like this: 25% of £70,000 is £17,500, less marginal relief of £250,000 minus £70,000, multiplied by 3/200 — £2,700. Tax due, £14,800, an effective rate of 21.1%.
With one associated company the limits halve, to £25,000 and £125,000. Same profit, new sum: 25% of £70,000 is still £17,500, but the relief is now £125,000 minus £70,000 times 3/200, which is £825. Tax due, £16,675.
£1,875 more tax on identical profits, for a structural decision that had nothing to do with trading. And the new company itself was not penalised at all — it made £20,000, which is still under its halved lower limit of £25,000, so it paid 19% either way. The cost fell entirely on the company that had been there all along.
The second company didn't pay a penny more tax. The first one did — for the offence of no longer being alone.
What counts as associated
Broadly, two companies are associated if one controls the other, or if the same person or people control both. Control is about rights and powers, not job titles, so it follows shareholdings, voting rights and entitlement to assets.
The rule is narrower than it first sounds in one important respect. Rights held by relatives and business partners are only attributed to you where there is substantial commercial interdependence between the two companies — financial, economic or organisational links such as one funding the other, sharing customers, sharing premises, sharing staff, or being run by the same management. Your spouse's entirely separate company is generally not associated with yours. Your spouse's company that operates from your unit, uses your staff and invoices through your systems very well might be.
There is also a genuine let-out for dormancy. A company that has not carried on any trade or business at any point in the accounting period is disregarded. That is worth knowing if you hold a name-protection company, though it works only while it truly does nothing — a company that traded for a single month in the year counts for that whole year.
Where it bites hardest
Not, in fact, at our level. The worst cases sit lower down and wider out. Take four associated companies: the limits become £12,500 and £62,500 each. A company making £50,000 would have paid 19% — £9,500 — standing alone. With four associates it pays 25% of £50,000 less £62,500 minus £50,000 times 3/200, which is £12,500 less £187.50, so £12,312.50.
That is £2,812.50 more tax on the same £50,000, an increase of nearly 30%, for a company whose trading has not changed in any way. Multiply that across a small group of four modestly profitable companies and the structure is costing real money every year.
What we would do differently
Ask the question before incorporating, not at the year end when the tax return is being prepared and the year is already closed. Twenty minutes with an accountant beforehand would have priced the decision.
Then genuinely test whether the new activity needs a separate company at all. A trading division inside the existing company, with separate management reporting, gives you most of the clarity and none of the tax cost. Waiting until the venture proves itself is often the better sequencing — you can always incorporate later and transfer the trade.
Where the reason for separation is real — different shareholders, genuinely different risk that you do not want touching the main trade, an intention to sell one and keep the other — the extra tax may well be the right price. Pay it knowingly rather than discovering it afterwards. And remember the second bill: two sets of accounts, two corporation tax returns, two confirmation statements and two bookkeeping jobs. For a small venture, the compliance cost often exceeds the tax cost.
The wider point is one that applies to most structural decisions in a small company. The tidy answer and the cheap answer are frequently not the same, and nobody in the process of incorporating a company is required to tell you which one you have chosen. If you are weighing how money comes out of the structure as well as how it sits inside it, how directors actually pay themselves covers the other half of the same conversation, and what a company director is personally liable for covers the risk side that often motivates the second company in the first place.
Common questions
What is an associated company for corporation tax?
Two companies are associated if one controls the other, or if the same person or persons control both. Control follows rights and powers — shareholdings, voting rights, entitlement to income or assets on a winding up — rather than who runs the business day to day. Rights held by relatives or business partners are attributed to you only where there is substantial commercial interdependence between the companies, meaning financial, economic or organisational links such as shared premises, shared staff, common customers, common management, or one company funding the other. The count includes companies anywhere in the world, not just UK-registered ones.
Does a dormant company count as an associated company?
No. A company that has not carried on any trade or business at any time during the accounting period is disregarded when counting associated companies. That gives a genuine let-out for a name-protection company or a shelf company that has never traded. The exemption is strict, though: it applies to the whole accounting period, so a company that traded for even part of the year counts for that year in full. If you are holding a dormant company, keep it genuinely dormant, file dormant accounts, and tell HMRC it is dormant for corporation tax purposes rather than assuming inactivity speaks for itself.
How much extra tax does a second company actually cost?
It depends entirely on where your profits sit relative to the halved limits. With one associate the thresholds fall from £50,000 and £250,000 to £25,000 and £125,000. A company making £70,000 pays £14,800 standing alone and £16,675 with one associate — £1,875 more on identical profits. Companies with profits comfortably below the reduced lower limit see no change at all, and companies already well above the upper limit were paying 25% anyway. The damage concentrates on profits sitting inside the marginal band, where the effective rate on each additional pound is 26.5%.
Should you set up a second company for a new venture?
Sometimes, but decide it deliberately rather than by default. Good reasons exist: a different shareholder group, genuinely different risk you want ringfenced from the main trade, or an intention to sell one activity while keeping the other. Against that, weigh the corporation tax cost of halved thresholds, plus a second set of accounts, corporation tax return, confirmation statement and bookkeeping — which for a small venture frequently costs more than the tax does. A trading division inside the existing company, with separate internal reporting, often delivers the clarity people are actually after, and you can always incorporate later.
