Deductions vs. Tax Credits

Definition

A deduction is subtracted from income before tax is calculated, so its value is the filer's marginal rate times the deduction amount. A non-refundable tax credit is subtracted from tax payable after tax is calculated, and federal non-refundable credits are valued at the 15% lowest-bracket rate regardless of the filer's marginal rate. Refundable credits, by contrast, can create a refund even when no tax is owing.

Key rules

• Deductions reduce taxable income (Line 26000). They flow through every bracket above and below, so a high-income filer at a 33% federal marginal rate saves 33 cents on the dollar from a new deduction.
• Non-refundable credits reduce tax (Line 40425 and below). At the federal level they are computed at 15%. Provincial credits use each province's lowest rate.
• Non-refundable credits cannot be carried forward unused (with a few exceptions such as donation carryforward and tuition).
• Refundable credits (GST/HST credit, Canada Workers Benefit, Canada Child Benefit) are paid even when tax payable is zero.
• Some items look like credits but are actually deductions (RRSP contributions, union dues, child care expenses). Read the line name carefully.

Example

Compare a $5,000 RRSP deduction and a $5,000 charitable donation (first $200 at 15%, remainder at 29%) for an Ontario resident with $180,000 taxable income whose federal marginal rate is 29%.

RRSP deduction:
  $5,000 x 29% federal  = $1,450 federal tax saved
  plus provincial marginal saving (~11.16% in ON) ≈ $558
  Total approximate savings: $2,008

Charitable donation credit (federal portion only):
  First $200  x 15%     =   $30
  Next $4,800 x 29%     = $1,392
  Total federal credit  = $1,422
  (Plus a parallel provincial donation credit)

The RRSP deduction and the donation both produce meaningful tax savings, but through different mechanisms. Deductions scale with income; most credits do not.

Common mistakes

• Treating a large non-refundable credit as "wasted" instead of planning to transfer it (spousal credit, tuition transfer to parent or grandparent up to $5,000).
• Assuming credits scale with marginal rate. They do not (at the federal level), so a $10,000 deduction is much more valuable than a $10,000 credit for high earners.
• Forgetting provincial layers. Both provincial tax and provincial credits are calculated separately.
• Claiming medical expense credit without meeting the lower-of-3%-of-net-income-or-$2,833 (2025) threshold.

Related concepts

The deduction-versus-credit distinction is implicit in every line of the T1 return. It is essential for reading the federal tax brackets correctly and for valuing the Basic Personal Amount. For owner-managers, the RRSP deduction is usually the single largest lever available at the personal level.