The Hidden Tax Problem Many Incorporated Dentists Don't Realize They Have
20 May 2026 · 7 min read
A profitable Professional Corporation feels like the end of the tax conversation. For many dentists, it is only the beginning - and the cost of an incomplete structure compounds quietly for decades.
The Assumption That Costs Dentists Millions
Incorporation is not the finish line. For many dentists, the structure that protects active income quietly erodes long-term wealth.
There is a belief that runs quietly through the incorporated dental community in Ontario - that once you have set up your Professional Corporation, saved diligently inside it, and accumulated a meaningful balance of retained earnings, you have done the hard work. The corporation is your vault. The money is safe. The tax problem is solved.
That belief, while understandable, is incomplete. For many dentists, the gap between what they assume and what is actually happening inside their corporation is costing them significantly - not in a single dramatic event, but slowly, year after year, through a mechanism most advisors never explain clearly.
How the Corporation Becomes a Tax Problem
The deferral is real. But the moment retained earnings are invested, a second set of rules takes over.
When a dentist incorporates in Ontario, the primary benefit is well understood: active business income earned inside the Professional Corporation is taxed at the small business rate - currently 12.2% in Ontario on the first $500,000 of active income, compared to a personal marginal rate that can reach 53.53% at the top bracket.
The problem begins when that retained, tax-deferred income is invested inside the corporation. Under ITA Section 129 and the rules governing Aggregate Investment Income, passive investment income earned inside a CCPC is taxed at approximately 50.17% in Ontario.
Worse, under ITA Section 125(5.1), if a CCPC earns more than $50,000 of passive investment income in a year, its small business deduction begins to phase out. For every dollar of passive income above $50,000, the small business limit is reduced by $5. At $150,000 of passive income, the deduction is eliminated entirely - and the corporation pays roughly 26.5% on active income instead of 12.2%.
A Real-World Illustration
The numbers compound quietly, but they compound predictably.
Consider Dr. Priya, a 44-year-old dentist in Mississauga who has been incorporated for twelve years. Her PC has accumulated $1.8 million in retained earnings, invested in a mix of GICs, mutual funds, and dividend-paying Canadian equities. Her portfolio generates approximately $85,000 per year in passive income.
Because her passive income exceeds $50,000, her small business deduction begins to phase out: ($85,000 - $50,000) x $5 = $175,000 reduction. Her effective small business limit drops from $500,000 to $325,000. Income above $325,000 that would previously have been taxed at 12.2% is now taxed at 26.5% - a 14.3 percentage-point gap on potentially hundreds of thousands of dollars.
On top of this, the $85,000 in passive income itself is taxed at roughly 50.17%. Over a ten-year horizon, the compounding effect of this inefficiency can represent hundreds of thousands of dollars in unnecessary tax.
The Retained Earnings Trap at Death
A second dimension is rarely discussed - and is even more consequential.
Under ITA Section 70(5), a taxpayer is deemed to have disposed of all capital property at fair market value immediately before death. For a dentist who owns shares of their PC, the shares are deemed disposed of at fair market value - which includes the retained earnings accumulated inside the corporation.
The estate pays capital gains tax on that deemed disposition. The corporation then still holds the retained earnings, which are taxed again when distributed to the estate or beneficiaries as dividends. This is the double taxation problem - one of the most significant and avoidable wealth destruction events in the incorporated professional's financial life.
"Wealth that is unstructured is not wealth - it is exposure."
The Capital Dividend Account, governed by ITA Section 83(2), is one of the primary tools used to address this. Corporate-owned life insurance, structured correctly, can create a significant CDA credit at death, allowing the corporation to distribute funds to the estate on a tax-free basis.
What Sophisticated Planning Looks Like
The dentists who navigate this well are not earning more than their peers. They are structured differently.
A Holding Company can receive inter-corporate tax-free dividends from the PC, separating active operations from accumulated wealth and creating planning flexibility outside the passive income regime.
A properly designed Individual Pension Plan creates tax-deductible employer contributions for the corporation, builds a defined-benefit retirement asset, and reduces the passive income base inside the PC.
Tax-exempt corporate-owned permanent life insurance bypasses the passive income rules entirely, accumulates on a tax-sheltered basis, and creates CDA credits at death that solve the double taxation problem at the source.
The structure is the strategy.
Incorporation creates the opportunity. What is built inside the corporation - the Holdco, the IPP, the tax-exempt insurance, the dividend strategy, the estate plan - determines whether that opportunity becomes lasting family wealth or quietly leaks away each year.
The dentists who get this right do not necessarily earn more. They simply build a structure that respects how the rules actually work.
