You've been building surplus inside your corporation. Good. You've invested it. Also good. But here's a question most business owners never think to ask:
What does it actually cost you to rebalance that portfolio?
Not the trading fees. Not the management expense ratio. The tax. Specifically, the corporate tax triggered when you realize gains - and the second, hidden layer of tax that most accountants don't show you on a single page.
I'm talking about the SBD grind-down. And for incorporated business owners in Quebec, it can push your effective corporate tax rate on investment income past 120%.
That's not a typo. Let me walk through why.
How Passive Income Grinds Down Your Small Business Deduction
Since 2019, the federal government has tied your access to the Small Business Deduction directly to how much passive income your CCPC earns. The rule is mechanical:
Under $50,000 in adjusted aggregate investment income (AAII): full SBD. Your first $500,000 of active business income stays at the small business rate. Between $50,000 and $150,000: the SBD shrinks. For every $1 of AAII above $50,000, you lose $5 of SBD room. Above $150,000: the SBD is gone entirely.
The numbers are simple. The consequences are not.
Two Taxes on One Dollar of Passive Income
When your corporation earns a dollar of investment income, two things happen simultaneously.
First, that dollar is taxed at the corporate investment income rate. In Quebec, that's about 50.17% combined federal and provincial. Part of that (30.67%) is refundable through RDTOH when you pay dividends, so the permanent cost is roughly 19.5%. Standard stuff.
Second - and this is what most people miss - that dollar of AAII erases $5 of your SBD room. Those five dollars of active business income now move from the small business rate (12.2%) to the general corporate rate (26.5% in Quebec). That's an additional 14.3% on each of those five dollars, or 71.5 cents of extra tax triggered by that single dollar of passive income.
Add it up: 50.17 cents in direct tax, plus 71.5 cents in SBD grind cost. That's $1.22 in corporate tax on $1 of passive income.
In Ontario, the picture is different. Ontario chose not to apply the passive income grind to its provincial SBD. So the grind only hits the federal portion - 6% on those five dollars instead of 14.3%. The total marginal rate in Ontario's grind zone lands around 80%. Still painful, but not the same structural penalty as Quebec.
The Three Zones
Think of your corporation's passive income as falling into one of three zones. Each requires a different approach.
What the Grind Costs You in Real Dollars
Your CPA knows the passive income rules exist. But the rules create a timing problem that rarely gets discussed in practical terms.
Say your corporation has $500,000 in active business income and a $2 million investment portfolio that needs rebalancing. The portfolio has $200,000 in unrealized gains. At a 50% inclusion rate, that's $100,000 of AAII if you crystallize everything.
In Quebec, that $100,000 of AAII would cost your corporation about $121,670 in total tax - the direct investment tax plus the SBD grind on your active income. The grind alone adds roughly $71,500 in extra tax beyond what the passive income itself would generate.
Now consider the alternative: you crystallize $100,000 of gains this year ($50,000 AAII - right at the threshold) and $100,000 next year. Total AAII each year: $50,000. Total grind cost: zero. Same rebalancing, dramatically different tax result.
Or the opposite situation: something forces you to realize $300,000 in gains this year ($150,000 AAII). The SBD is gone regardless. Might as well realize the remaining $200,000 of gains in the same year, because the marginal rate on that additional income is back down to about 50% - not 122%.
This example is illustrative only. Actual results depend on your specific corporate structure, associated corporations, and income composition. Consult your CPA.
SBD Grind-Down Calculator
Plug in your expected active business income and your projected investment income. Watch what happens to the marginal rate as passive income increases. Move the sliders and see where the safe zone ends, where the grind zone peaks, and what a specific rebalancing decision would actually cost you.
If your passive income is above $50,000, the calculator opens additional panels: the RDTOH two-pool breakdown, the salary extraction comparison, and a full waterfall table showing where every dollar ends up.
Marginal tax rate on passive income
What does additional passive income cost you?
| Additional AAII | Total extra corporate tax | Effective rate | Net of RDTOH |
|---|
Timing Considerations
Important notes
This calculator illustrates the corporate-level tax impact of the SBD passive income grind-down. It uses 2025 combined federal and provincial tax rates. Actual results depend on your specific corporate structure, associated corporation rules, taxable capital, and the composition of your investment income.
Capital gains inclusion rate: 50% (current law). The AAII threshold is based on the prior tax year's investment income. This tool shows the current-year impact for illustration purposes.
This is educational and does not constitute personalized advice. Work with your CPA and tax professional to evaluate your specific situation before making rebalancing decisions.
Mutual funds are offered through WhiteHaven Securities Inc. Insurance products and other services are offered through iAssure Inc. iAssure Inc. activities are neither the business nor the responsibility of WhiteHaven Securities Inc.
"But I Get It Back on Dividends"
If you've been reading carefully, this is the natural objection. And it's half-right.
When your corporation earns passive income, part of the tax (30.67%) goes into RDTOH. When you eventually pay taxable dividends, you get that portion back. So the direct tax on passive income isn't as bad as it looks - about 19.5% net after the refund.
But the RDTOH refund applies to the direct tax on the passive income. It does nothing about the grind damage on your active income. These are two completely separate pools of tax.
Pool 1 is the tax on your passive income itself. RDTOH works here. It reduces the permanent cost. This works the same whether your AAII is $30,000 or $130,000.
Pool 2 is the extra tax on your active business income - the SBD room you lost because passive income ground it down. This gets added to your corporate tax bill with no refund mechanism at all. Not through RDTOH. Not through any other channel. It's permanent.
So when someone in Quebec has $500,000 of active income and $100,000 of AAII, the 122% marginal rate includes about 50% in direct passive tax (partly refundable through RDTOH) and about 72% in grind damage on the active income side (fully permanent). RDTOH brings the direct portion down. It leaves the 72% untouched.
The calculator breaks this into two side-by-side pools so you can see exactly which tax is refundable and which is permanent.
Should You Extract Extra Salary?
Here's where the grind creates a genuinely counterintuitive situation.
Every incorporated business owner in Canada knows the fundamental tension: money inside the corporation is tax-sheltered, but extraction costs 40-53% in personal tax. So you defer. You leave money in the corp as long as possible because pulling it out is expensive. That's the default strategy, and most of the time it's the right one.
The grind breaks this logic.
When your corporation is paying more than 100% tax on the next dollar of passive income, the math flips. Paying yourself additional salary reduces your active business income, which restores SBD room, which drops the corporate tax rate back to the small business rate. The salary costs you roughly 53% personally in Quebec. But the corporate tax recovery from the salary deduction can be just as large - or larger.
The calculator's waterfall table makes this visible step by step. Section A shows cash in the corporation before any extraction. It compares two parallel scenarios - one with passive income, one without. You'll see how much the grind actually costs: the amber summary line shows how little the corporation keeps from the passive income after grind damage. In many cases, the corporation keeps only a fraction of what passive income brought in.
Section B then asks: what if you extract extra salary? Starting from Section A's ending cash, it subtracts the salary, then adds back the corporate tax recovered because salary is a deductible expense. This is where the numbers tell the real story. The recovery in the passive-income scenario is dramatically larger - because the salary is not only saving the SBD rate, it is clawing back grind damage.
The personal side is identical in both scenarios. Same salary, same personal tax rate, same after-tax cash in your pocket. The difference shows up entirely in the corporation.
The green summary row shows what passive income actually nets after extraction. With $500,000 of active income and $170,000 of AAII, extracting all active income as salary can still leave about $85,000 more total wealth than in a no-passive-income scenario. The passive income still adds value when salary is used to neutralize grind damage.
This works above $150,000 AAII too. When you extract all active income as salary, the grind has nothing left to affect - ABI goes to zero. The passive income sits in the corporation, taxed at its own rate, and roughly half survives. That's money that wouldn't exist in a no-passive-income scenario.
What Else You Can Do
Beyond the salary route, there are structural strategies that tax professionals commonly identify:
Annual gain harvesting at $50,000 AAII. Crystallize gains each year up to the threshold, then stop. This requires knowing your other sources of investment income - interest, rent, dividends from non-connected corporations - and leaving room for them.
Bunching realizations above $150,000. If a major event pushes AAII past the threshold - a property sale, a large distribution, a forced rebalancing - it may cost less to crystallize all your deferred gains in the same year rather than spreading them into future years where each year falls into the grind zone.
Reducing AAII through structure. Corporate-owned life insurance policies that qualify as exempt policies don't generate AAII on the growth inside the policy. Moving surplus from taxable investments into an exempt policy can reduce future AAII while building tax-sheltered value. This doesn't eliminate the passive income that's already been earned, but it changes the trajectory going forward.
Each of these requires coordination with your CPA and tax professional. The calculator shows you the cost. Your professional team designs the solution.
Accidental or Planned?
Most business owners I work with are sitting on unrealized gains they've been meaning to address. The gains keep growing, the rebalancing keeps getting deferred, and nobody has shown them what the grind actually costs in dollars.
Now you've seen it. And you've seen something else most owners never consider: the grind can make the usually expensive act of extraction cost dramatically less - sometimes nothing at all. The thing you've spent years deferring becomes the rational move when the corporation is paying more than 100% tax on the next dollar.
That window exists every year your passive income lands above $50,000. You can use it deliberately, or you can let the grind happen by accident. The math is the same either way. The outcome isn't.
Related Reading
Corporate whole life insurance case study - How exempt policies reduce AAII and the SBD grind-down collateral cost.
Corporate investment strategies - Tax-efficient portfolio structure for incorporated business owners.
Want to See These Numbers for Your Situation?
If you want to model the grind with your actual portfolio, income levels, and corporate structure, that's where a conversation starts.