The profit test comes first
The corporation earns its keep through deferral. Profit retained inside is taxed at about 12.2% on the first $500,000 of active income in Ontario, while the same dollar on a sole proprietor's T1 can face up to 53.53%. A shop that banks $40,000 it did not draw keeps five figures of extra working capital in the company every single year, which is what buys the next van and carries the crew through February. If every dollar the business makes goes out the door to live on, the deferral is theoretical and the corporation can wait without costing you much.
Growth changes that math quickly. The season you add a second truck and a first employee is usually the season retained profit appears, which is why incorporation and hiring tend to arrive together for service companies.
The other two signals: exposure and counterparties
Plumbing carries tail risk most trades do not. A failed fitting or a missed shutoff can flood a finished basement weeks after the truck left, and the claim arrives long after the invoice was paid. Insurance is the first line of defence; the corporation keeps whatever exceeds it pointed at the business rather than your house. The honest caveat: you always remain responsible for your own negligent work, so the corporate shield protects savings and family assets, not your licence.
Counterparties push in the same direction. Builders and GCs issuing T5018s would rather contract with a corporation than with a person and a SIN, larger bids read differently with a corporate balance sheet behind them, and your first hires put payroll obligations somewhere other than your personal name.
What actually has to move
Incorporating a plumbing business is never just articles. The operating pieces re-issue in the corporate name, and missing one causes weeks of friction on job sites and at the supply counter:
- Municipal contractor licence. GTA municipalities license plumbing contractors, with a master plumber named on the licence, and the corporation needs its own.
- WSIB. Construction is mandatory-coverage territory, so the corporation registers its own account, and GCs will ask for clearance certificates under the new number before releasing payment.
- HST. The corporation is a new taxpayer with a new business number; the sole proprietor account closes with a final return.
- Insurance, suppliers and financing. Liability policies, Wolseley or Emco credit terms and any van loans all need consents and re-papering in the corporate name.
The trucks, tools and equipment themselves can transfer in without triggering tax through a section 85 rollover, and an election generally keeps HST off the transfer of the business. That paperwork is where do-it-yourself incorporations most often go quietly wrong, surfacing years later as a phantom gain nobody planned for. One small bonus of the change: a corporation chooses its own fiscal year-end, so we usually park it in a slow month rather than letting year-end work collide with spring service season.
Sole proprietor vs corporation, in plumbing terms
| What changes | Sole proprietor | Corporation |
|---|---|---|
| Tax on profit left in the business | Your marginal rate, up to 53.53% | About 12.2% up to $500,000 |
| A flood claim beyond insurance | Personal assets in play | Corporate assets stand in front |
| T5018 slips from builders | Reported against your SIN | Reported to the corporation |
| Selling one day | Asset sale, fully taxable | Share sale may access the $1.25M capital gains exemption |
| Losses in a rough year | Offset your other personal income | Locked in the corporation until profits return |
That last row is the honest one. A first-year operation still finding its feet often benefits from losses flowing to a personal return, which is one more reason not to incorporate on day one just because a course or a forum said to.
Done once, with year one set up properly
Our Incorporation service handles the articles with share classes that leave room for later planning, the CRA program accounts, the rollover paperwork and a transition checklist for licences, WSIB, insurers and suppliers, quoted in writing after a free 15-minute discovery call. Many new corporations pair the first year with CPA Quick Support at $99/month for unlimited questions while the corporation is new, or step straight into End-to-End Accounting when there is already a crew to pay. The first year-end sets the pattern for the ten after it, and it is much cheaper to set it right than to repair it.
