Owners often incorporate a second company for a clean reason: a new venture, a property, a spouse’s practice. The tax cost only appears at year end, when both corporations compete for the same low-rate room. Here is how the sharing rules work and where they bite.
Key Takeaways
- The $500,000 business limit belongs to a group of corporations, not to each one in it.
- Control is tested by votes and by fair market value, so a “silent” 51% shareholder still associates two companies.
- Without a filed allocation agreement, the CRA can assign the limit for you.
- Passive income and taxable capital grind the limit before anyone divides it.
- Ontario did not copy the federal passive income grind, so your federal and provincial limits can differ.
What the Small Business Deduction Is Worth in 2026
The small business deduction is a 19% rate reduction under subsection 125(1) of the Income Tax Act. It applies to the least of three amounts: active business income earned in Canada, taxable income, and the business limit. That reduction, universally called the SBD, pulls the federal tax rate from 15% down to 9%.
| Active business income | Federal | Ontario | Combined |
|---|---|---|---|
| First $500,000, to June 30, 2026 | 9% | 3.2% | 12.2% |
| First $500,000, from July 1, 2026 | 9% | 2.2% | 11.2% |
| Above the business limit | 15% | 11.5% | 26.5% |
Ontario’s 2026 budget cut the provincial rate to 2.2% effective July 1, 2026, prorated for years that straddle that date. So a full calendar 2026 year lands near 11.7% combined. The gap between the low rate and 26.5% is roughly 14 to 15 points, which is why a shared limit costs real money. Our corporate tax advisory work starts here for most owner-managed groups.
How the Income Tax Act Decides You Have an Associated Corporation
Section 256 sets five tests. Two corporations are associated when:
- One controls the other, directly or indirectly in any manner whatever.
- The same person or group controls both.
- Each is controlled by a different person, those two people are related, and each owns at least 25% of the shares of any class of the other company.
- One is controlled by a person related to each member of the group that controls the other, and that person owns at least 25% there.
- Each is controlled by a related group, and a member of one group is related to every member of the other, with 25% cross-ownership.
Two extensions catch most people. Subsection 256(1.2) deems control to exist where someone owns shares worth more than 50% of the fair market value of all shares, so a non-voting freeze share can associate corporations that look independent on paper. Subsection 256(1.3) treats shares owned by a child under 18 as owned by the parent.
In our corporate tax practice, the association we uncover most often is not two operating companies. It is a holdco that a spouse controls and a second corporation nobody connected to it, discovered only when the CRA matched the shareholder registers.
Association Through a Third Corporation and the Schedule 28 Election
Subsection 256(2) reaches further. If Corporation A and Corporation B are each associated with Corporation C, then A and B are associated with each other, even though they share no direct ownership. A parent’s holdco sitting above two children’s businesses does exactly this.
There is an escape. Corporation C can file Schedule 28, electing not to be associated with A and B for business limit purposes. A and B then stop being associated through C and each keeps its own limit. The price is absolute: C’s own limit becomes nil for that year.
That trade only makes sense when the third corporation has no active business income to shelter, which is the usual holdco fact pattern. Read our holding company guide before you file it, because the election does not de-associate the corporations for any other purpose in the Act.
How Associated Companies Share the Business Limit on Schedule 23
Sharing is not automatic and it is not proportional. Every member of the group must sign Schedule 23, the allocation agreement, and the percentages cannot total more than 100%. File nothing and each corporation’s limit is nil, which converts low-rate income into 26.5% income overnight.
Subsection 125(4) lets the Minister step in and allocate the limit if the group does not file within 30 days of a written request. You want to make that choice yourself, because the sensible split sends the limit to whichever corporation actually earns the active income this year, not to last year’s winner.
Worked example. Dario controls a $600,000-profit contracting company and a $180,000-profit equipment rental company his wife runs. They are associated. Allocating $500,000 to the contractor and $0 to the rental company saves the group the most, because the contractor’s excess would otherwise sit at 26.5% while the rental company’s cheaper income does not need the room.
Two Grinds That Shrink the SBD Before You Split It
The group divides a reduced limit, not the headline $500,000. Subsection 125(5.1) applies the greater of two reductions, both measured across the whole associated group.
| Grind | Measured on | How it works | SBD gone at |
|---|---|---|---|
| Taxable capital | Group taxable capital employed in Canada, prior taxation year | Straight-line reduction once the group passes $10 million | $50 million |
| Passive income | Group adjusted aggregate investment income, prior calendar year | $5 of limit lost for every $1 above $50,000 | $150,000 |
The passive grind is the one that surprises owners, and the timing is why. It looks back to taxation years ending in the preceding calendar year. A one-time capital gain inside the group in 2025 quietly reduces the limit available in 2026, long after the cash is gone. That lag is worth planning around, and our guide to Schedule 7 shows where the figure is actually computed.
Here is the part almost nobody applies correctly: Ontario never adopted the federal passive income measure. A group ground down to a $200,000 federal limit still has the full $500,000 of SBD room available at the Ontario rate. Two different limits, one return, and tax software will not flag the difference for you.
Eligibility Traps for a Canadian-Controlled Private Corporation
Only a Canadian-controlled private corporation can claim the deduction, and only on active business income. Three exclusions strip it away:
- Specified investment business. A corporation whose principal purpose is earning income from property, such as rent or interest, unless it employs more than five full-time employees all year.
- Personal services business. An incorporated employee arrangement, taxed at 33% federally with no rate reduction available.
- Subsection 256(2.1). An anti-avoidance rule that deems corporations associated where one of the main reasons for their separate existence is reducing tax.
That last rule matters more than its low profile suggests. Splitting one business across two corporations to double the SBD is precisely what it targets, and a reassessment under it also drags in every year still open.
Common Mistakes That Cost the Deduction
- Treating the limit as $500,000 per corporation when the group shares one.
- Forgetting non-voting or preferred shares that trip the fair market value test.
- Missing shares held by a spouse, a family trust or a minor child.
- Filing the allocation agreement with percentages that add to more than 100%.
- Repeating last year’s split when the income has moved to another company.
- Filing Schedule 28 when the third corporation still earns active income.
- Applying the federal passive grind to the Ontario calculation as well.
Questions About the Small Business Deduction
Who qualifies for the small business deduction?
A Canadian-controlled private corporation qualifies on active business income earned in Canada, up to its business limit. Investment companies and incorporated employees do not. Public corporations and foreign-controlled companies are excluded entirely.
What is the definition of associated corporations in Canada?
Two corporations are associated when one controls the other, when the same person or group controls both, or when related shareholders each hold at least 25% cross-ownership. Section 256 sets the full tests and extends them to corporations linked through a third corporation.
How do associated corporations share the $500,000 limit?
They file Schedule 23 with their returns and agree on percentages that total no more than 100%. If they file nothing, each corporation’s limit is nil until an agreement is filed. The CRA can allocate the limit itself after a written request goes unanswered.
Do holding companies affect the group’s limit?
Yes. A holdco with no active income still counts as a member of the group, and its investment earnings feed the passive income grind that reduces the limit for everyone. Part of the tax on those earnings is refundable through the refundable dividend tax on hand pools, but the grind applies regardless.
Should the allocation be reviewed every year?
Yes, every single year. The right split follows this year’s income, and the group’s passive earnings from the prior calendar year change how much limit there is to divide. A stale agreement is one of the most common and most expensive filing errors we see.
The Bottom Line
Association is a status the Act imposes on you, not a structure you elect into. Once it applies, the planning shifts to allocating well and keeping passive earnings out of the grind.
- Map every shareholder, including spouses, trusts and minor children, before year end.
- Confirm which corporations are associated, then allocate the limit to where the income actually is.
- Track the group’s passive earnings, because this year’s number sets next year’s limit.
- Run the federal and Ontario calculations separately.
Group structures rarely stay still, and a share issued or a corporation added mid-year can change the answer for every member. If you own more than one corporation, a review before year end is worth far more than a correction after assessment. Talk to our corporate tax team about how your group should be filing.
