Medical Professional Corporation Rules in Ontario

The 7 Rules That Define a Medical Professional Corporation in Ontario

Incorporating a medical practice is not the same as incorporating an ordinary business. A physician's corporation is governed by the Business Corporations Act, the Medicine Act and the Regulated Health Professions Act, and is policed by the CPSO. Before any tax planning happens, the corporation has to be set up and maintained to the profession's rules. Our healthcare accounting team sets these up for doctors across Ontario. These are the seven rules that matter most.

1. CPSO Certificate of Authorization. A medical professional corporation cannot practise medicine until the CPSO issues a Certificate of Authorization, and that certificate must be renewed every year.
2. Voting shares held by the physician. All voting (and equity) shares of the corporation must be legally and beneficially owned by the member physician, or by physicians practising together.
3. Family members and non-voting shares. A spouse, child or parent of the physician (or a trust for a minor child) may hold non-voting shares, which opens limited income-splitting subject to the tax rules.
4. Corporate name format. The name must include the physician's name and the words "Medicine Professional Corporation," and it must comply with CPSO naming rules.
5. Permitted activities only. The corporation may only practise medicine and carry on activities related to or ancillary to that practice; it cannot run an unrelated business.
6. Professional liability is not limited. Incorporating does not protect a physician from personal liability for their own professional negligence; the CPSO and malpractice obligations still attach to the individual.
7. Tax rules govern the benefit. The real advantages, deferral and limited income splitting, are shaped by the small business deduction and the Tax on Split Income (TOSI) rules, not by incorporation alone.

1. The CPSO Certificate of Authorization

This is the rule that comes before everything else. A corporation can be created at the provincial registry in a day, but it cannot practise medicine or bill for a physician's services until the CPSO has issued a Certificate of Authorization. The application confirms that the share structure, name and directors meet the College's requirements. The certificate is not one-and-done either: it must be renewed annually, and the corporation must stay compliant in between. Setting the company up so the CPSO will approve it the first time is where a healthcare-experienced advisor saves real time.

2 & 3. Who Can Own the Shares

Share ownership is the most misunderstood part of a medical professional corporation. All voting shares must be owned by the physician. Where doctors practise together, the voting shares can be held among those physicians. What changed the planning landscape is the treatment of family shareholders: a spouse, children and parents of the physician may own non-voting shares, but whether dividends paid to them are taxed at the family member's rate or at the highest rate depends entirely on the Tax on Split Income rules. The structure that was standard before 2018 does not automatically deliver income splitting today.

4. The Corporate Name

A medical professional corporation cannot be called whatever the physician likes. The name must contain the surname of the physician as it appears on the CPSO register, followed by "Medicine Professional Corporation," for example "Dr. Jane Smith Medicine Professional Corporation." The CPSO reviews the name as part of the Certificate of Authorization. A name that does not comply will hold up the entire approval.

5. What the Corporation Is Allowed to Do

A medical professional corporation may only practise medicine and carry on activities ancillary to that practice, such as investing the earnings the practice generates. It cannot operate an unrelated active business through the same corporation. This restriction matters for tax planning: retained earnings can be invested inside the corporation, but the corporation cannot become a vehicle for a separate commercial venture without stepping outside the CPSO rules.

6. Liability: What Incorporation Does Not Do

Many physicians assume incorporation puts a wall between them and a malpractice claim. It does not. A medical professional corporation does not shield the physician from personal liability for their own professional negligence, and CPSO obligations remain personal. The corporation provides tax and administrative structure, not protection from a professional claim. Appropriate professional liability protection through the CMPA remains essential.

7. How a Medical Professional Corporation Is Actually Taxed

This is where the value is, and where it is most often overstated. Active medical income earned in the corporation that qualifies for the small business deduction is taxed at a low combined Ontario rate, far below a high-earning physician's personal rate. That gap creates a deferral: money left in the corporation is taxed lightly now, and personal tax applies only when it is drawn out. The corporation does not make the tax disappear; it defers it and gives the physician control over the timing. Income splitting with family is possible but limited by TOSI, and investment income earned inside the corporation is taxed at high rates and can grind the small business limit. A medical corporation is a powerful tool, used correctly.

A Simple Worked Comparison

Consider a physician billing $400,000 a year who needs $180,000 personally to live on:

Unincorporated, the full $400,000 is taxed at personal rates this year. Incorporated, only what the physician draws is taxed personally now, and the rest stays in the corporation taxed at the low active rate, available to invest or draw in lower-income years. The benefit is deferral and control, not a permanent saving, which is exactly why a corporation should be run with a CPA who plans the draws. Our accounting for doctors and healthcare practices is built around exactly this.