Introduction
The small business deduction limits the combined federal-provincial tax rate to approximately 12.2% (Ontario, 2026) on the first $500,000 of a CCPC's active business income. Income above $500,000 is taxed at the general corporate rate — approximately 26.5% in Ontario. The difference in rates on the marginal dollar above $500,000 is approximately 14.3%.
For a corporation whose net active income is in the range of $400,000–$600,000, the interaction between the SBD limit, compensation strategies, and the general rate pool creates planning opportunities that are worth understanding before they become relevant.
The $500,000 Threshold: What Triggers the Reduction
The SBD applies to active business income up to the "business limit" — $500,000 federally, which Ontario matches. For income above this threshold, the general corporate rate applies automatically. There is no election to stay under the limit; it is a hard boundary.
A corporation with $520,000 of net active income pays the small business rate on $500,000 and the general rate on $20,000. The general rate on $20,000 is approximately $5,300 — compared to $2,440 at the SBD rate. The incremental cost of that $20,000 above the limit is approximately $2,860 in additional corporate tax.
Strategy 1: Salary to Keep Income Under the Limit
A controlled, deliberate salary draw can reduce corporate taxable income to stay at or below $500,000. A physician or dentist whose MPC is projecting $560,000 of net income can draw an additional $60,000 in salary before year end — reducing corporate taxable income to $500,000, keeping the full SBD available.
The personal tax on that $60,000 of additional salary (at a marginal rate of approximately 46–53%) is the cost of preserving the SBD on $60,000 of corporate income. The personal tax is approximately $27,600–$31,800. The corporate SBD saved is approximately $8,580. The net direction of this analysis depends on the marginal rate — at 53%, the personal tax is $31,800 and the corporate saving is $8,580; drawing the salary is not worth it. But the additional salary also generates RRSP room, creates a corporate deduction, and may serve the compensation plan for other reasons.
This illustrates why the threshold strategy is not mechanical — the salary draw to preserve SBD is only worth the personal tax cost if the marginal rate on the salary is lower than the combined corporate-plus-personal rate on the excess corporate income.
Strategy 2: Immediate Expensing or CCA to Reduce Corporate Income
As discussed in Article 148, a large capital equipment purchase — with immediate expensing claimed in the year — can reduce corporate taxable income materially. A corporation projecting $550,000 in active income that purchases $60,000 of eligible equipment and claims immediate expensing reduces taxable income to $490,000 — below the SBD limit.
This is only beneficial if the equipment purchase was planned anyway. Buying equipment purely to reduce income below the SBD limit requires the $60,000 equipment purchase to generate more than $8,580 in SBD tax savings — which it almost certainly does not, unless the equipment has real business utility.
Strategy 3: Associated Corporation SBD Sharing
CCPCs that are associated share the $500,000 business limit. A professional who operates through two associated corporations — for example, a physician with an operating MPC and an active consulting corporation — must divide the $500,000 limit between them. The combined SBD-eligible income across both corporations is capped at $500,000.
For professionals managing multiple active entities, this sharing rule requires that the total compensation structure across all corporations is coordinated to ensure the SBD is not inadvertently fragmented inefficiently.
Strategy 4: Increasing Compensation as Income Grows
The most straightforward threshold management strategy: as the corporation's income grows toward and past $500,000, the compensation level drawn by the shareholder-employee should be reviewed and calibrated to keep corporate taxable income at or near the SBD limit. This is not an avoidance strategy — it is ordinary compensation planning that reflects the marginal benefit of the SBD.
When to Speak With a CPA
The SBD threshold is an annual conversation. As the corporation's income grows — through market growth, practice expansion, or price increases — the point at which it crosses $500,000 approaches. Planning in November, with a full-year income estimate, allows compensation timing decisions that manage the threshold efficiently.