A second company can increase the Corporation Tax bill of the first one, even if the first company’s profits have not changed.
This is because of the associated companies rule. Where companies are under common control, the £50,000 and £250,000 Corporation Tax thresholds are divided between them. So a company that would otherwise pay 19% on all of its profits can find itself pushed into marginal relief simply because another company is now associated with it.
That can make a surprisingly large difference to the tax bill, particularly where profits sit around the lower threshold.
This guide explains how the rule works, which companies count, how the thresholds are reduced, and what to watch for if you own or control more than one company.
Why an Additional Company Can Raise Your Tax
A standalone company with profits of £50,000 or less will normally pay Corporation Tax at 19%, which is lower than the 25% charged on larger profits.
You might expect every company you own to get its own £50,000 taxed at that cheaper rate, but it doesn’t necessarily.
HMRC treats companies under the same control as connected, and divides that £50,000 threshold between them. So the more companies you control, the lower each one’s threshold for a cheaper rate, and the more of its profit is taxed at a higher rate instead.
The rule exists to stop people splitting one business across several companies purely to claim the cheaper rate over and over.
But it applies whether or not that’s what you’re doing, and plenty of directors are caught simply because they happen to own more than one company.
A Worked Example
Take Company A, which makes £45,000 of profit a year. If it’s the only company you own, its full £45,000 sits within the £50,000 threshold and is taxed at 19%. Its Corporation Tax bill is £8,550.
Now you start a second company, Company B. The two are associated, so Company A’s threshold is halved to £25,000. It still earns the same £45,000, but only the first £25,000 is taxed at 19%. The £20,000 above the threshold is now exposed to the higher rate that applies in the middle band – an effective 26.5%, as the next section explains – and Company A’s bill rises to £10,050.
That’s £1,500 more a year, on identical profit, purely because a second company now exists. Add a third company and the threshold falls to about £16,667; a fourth, and it’s £12,500.
Every company you add pushes more of the others’ profit onto the higher rate.
What the Higher Corporation Tax Rate Is
Profits between £50,000 and £250,000 are charged at 25%, then reduced by something called marginal relief, which brings the effective rate down so it climbs gradually from 19% to 25% as profits grow. The reduction shrinks as profits rise and ends entirely at £250,000.
Even with marginal relief holding the overall rate below 25%, each extra pound of profit in that band is effectively taxed at 26.5% – more than the headline rate.
So when the associated companies rule pushes your profit above the 19% threshold, that profit isn’t taxed at 25%. It’s taxed at 26.5%, which is why the cost climbs faster than you’d expect.
Both the lower and upper thresholds are divided between associated companies the same way.
With two companies they halve, to £25,000 and £125,000; with three they fall to roughly £16,667 and £83,333, and so on.
| Companies under common control | 19% rate applies up to | 25% rate applies above |
|---|---|---|
| One | £50,000 | £250,000 |
| Two | £25,000 | £125,000 |
| Three | £16,667 | £83,333 |
| Four | £12,500 | £62,500 |
Each company gets the reduced thresholds. So two companies don’t share a single £50,000 band between them – each one’s band drops to £25,000.
Which Companies Count as Associated
Whether the rule applies to you depends on how many associated companies you have, and the answer isn’t always obvious.
A company counts if you control it – broadly, if you hold more than half its shares, votes, or rights to its income or assets. On that test, the following all count towards your total:
- Any company you control, whether it trades or simply holds investments.
- Companies based overseas, if they’re under the same control. Where a company is registered makes no difference.
- A company associated for only part of the year, which still counts for that year.
Two kinds of company are left out of the equation:
- Dormant companies. A company that carried on no trade or business during the year doesn’t count. So a company you set up and never used shouldn’t affect the others.
- Certain passive holding companies. A holding company that does nothing but own shares in its subsidiaries and pass on dividends can sometimes be excluded – but the conditions are strict, so don’t assume it applies.
A Note on Property Companies
A company that exists mainly to hold investments – a “close investment-holding company” – doesn’t get the 19% rate or marginal relief at all. It pays 25% on all its profits, whatever they are.
A company that simply lets property to unconnected tenants usually falls outside that definition, but it’s worth checking, because where it applies it changes that company’s position entirely.
If two companies split £50,000 of profit, do you pay more tax?
It depends on how the £50,000 profit is split between them.
With one company, the 19% Corporation Tax threshold is £50,000. With two associated companies, that threshold is cut to £25,000 for each company.
- One company makes £50,000: tax is £9,500
- Two companies make £25,000 each: each stays within its £25,000 threshold. Total tax is still £9,500.
- Two companies make £40,000 and £10,000: the £40,000 company is £15,000 over its £25,000 threshold and moves into marginal relief. The £10,000 company has £15,000 of its threshold unused, but it cannot transfer that unused amount to the other company. Total tax is £10,625.
So the same £50,000 of total profit can produce a higher Corporation Tax bill simply because it is split unevenly between two associated companies.
In this example, the extra tax is £1,125.
Your Spouse’s Company Doesn’t Automatically Count
Families often assume that if you own one company and your spouse owns another, the two must be associated. Usually they aren’t, and the point is widely misread.
For your companies and your spouse’s to share thresholds, HMRC would have to treat your spouse’s control of their company as if it were yours.
It only does that where the two businesses are genuinely commercially linked – what the rules call “substantial commercial interdependence”.
Without that link, your spouse’s separate company doesn’t count towards your total. (If you personally control both companies in your own right, they’re associated regardless; the interdependence test only matters where the connection would otherwise run through a relative.)
“Substantial commercial interdependence” means the two businesses genuinely rely on or work with each other. HMRC looks for three kinds of link. It isn’t necessary for all three to exist – a sufficiently substantial link of one kind can be enough:
- Financial: one company lends to or financially supports the other, or they share a financial stake in the same venture.
- Economic: they share customers, work towards the same commercial aim, or one company’s activities benefit the other.
- Organisational: they share management, employees, premises or equipment.
The word doing the work is “substantial”. A minor overlap isn’t enough – HMRC has accepted that two companies run from the same family home, sharing a phone line, weren’t sufficiently linked.
So a plumber whose company is entirely separate from their spouse’s unrelated marketing firm – different customers, premises, staff and finances – won’t usually find the two associated.
But where one company funds the other, or they genuinely share management and premises, that can change. If your businesses really are independent, keep evidence of it – separate premises, customers and staff, and proper records of any dealings between them – in case HMRC asks.
What To Do About Associated Companies
You can’t switch the rule off, but you can make sure it isn’t costing you more than it should:
- Count your companies once a year: List every company you and your close family control – active, dormant, holding and overseas – so you know your true number.
- Close or clear out dormant companies you don’t need: A dormant company stays out of the count, and striking it off removes any doubt.
- Keep separate businesses genuinely separate: If you and your family run unrelated companies, avoid financial, economic, and organisational links between them to keep them from becoming associated and to protect your thresholds.
- Watch the timing near a threshold: Because the rate depends on profit levels, when profit falls and how long an accounting period runs can affect the rate a company pays. Review this with an accountant when a company’s profits are close to a threshold.
Beware that active trading subsidiaries all count, so a group of them shares the thresholds just as separate companies would. Only a genuinely passive holding company can sometimes be excluded, and only on the strict conditions above.
Can You Give Up Control and Still Keep a Share of the Profits?
Potentially. The associated companies rules are based on control, not simply whether you own shares in more than one company.
That means a company doesn’t necessarily have to be associated just because you keep an investment in it. If you genuinely give up control, you may still be able to keep a minority shareholding and receive dividends without the company being treated as one you control.
But the detail matters. HMRC’s definition of control is wider than voting rights alone. It can include:
- Voting power – who can actually control shareholder decisions.
- Share capital – who owns the greater part of the company’s shares.
- Income rights – who’s entitled to the greater part of the company’s income if it’s distributed.
- Asset rights – who’d be entitled to the greater part of its assets in a winding-up.
So simply giving someone else 51% of the voting shares doesn’t necessarily solve the problem if you keep other rights that still give you control.
The same applies if shares are transferred to a spouse or another family member. If the businesses are substantially commercially interdependent, their rights may still be taken into account when HMRC decides who controls the companies.
For someone building several businesses, this makes ownership structure an important part of the planning. You don’t necessarily need to own and control 100% of every venture to keep benefiting financially.
But any change in ownership needs to be a genuine transfer of control. You can’t give control away on paper while keeping it through another share class, agreement or arrangement.
How Double Point Can Help
At Double Point, we make sure the associated companies rule is applied correctly for every business we look after, so you never pay a higher rate of Corporation Tax than you should.
That means counting your associated companies properly, applying the right thresholds, working out any marginal relief accurately, and noticing where a forgotten dormant company or a family arrangement is quietly costing you.
If you run more than one company, or you’re thinking of starting a second, we can show you what it means for your tax before you commit, as part of your wider tax planning. We’ll also handle the accounts and returns for each one, so the whole picture stays consistent.
If you’d like to know whether the associated companies rule is affecting your bill, book a free consultation and we’ll take a look.
Disclaimer: General information only, not advice. Rules and figures can change. Take advice on your own circumstances before acting.