Ontario Surtax
Surtaxe de l'Ontario in French
Quick definition
The Ontario surtax is a tax on your Ontario tax, not on your income: 20% of Ontario basic tax above a first threshold, plus 36% above a second. It quietly pushes Ontario's real rates well above the posted brackets.
A tax on a tax
Most taxes apply to income. The Ontario surtax applies to Ontario basic tax, the provincial tax you have already calculated from the brackets and credits. For 2026 (as of July 2026), it is 20% of Ontario basic tax above $5,818, plus an additional 36% of Ontario basic tax above $7,446. The tiers stack: past the second threshold, both apply at once, a combined 56% on every extra dollar of provincial tax.
Where it starts to bite
In income terms, the 20% tier typically kicks in around the low $90,000s of taxable income, and the 36% tier somewhere around $115,000 to $120,000. Both figures are approximate: the surtax is triggered by your Ontario basic tax, so every provincial credit you claim pushes the trigger points a little higher.
The multiplier on your marginal rate
Because the surtax is a percentage of your tax, it multiplies your provincial marginal tax rate. In Ontario's 9.15% bracket with the 20% tier active, the effective provincial rate is 9.15% × 1.20, or 10.98%. In the 11.16% bracket with both tiers active, it is 11.16% × 1.56, about 17.41%.
This is how Ontario's top combined rate reaches 53.53% (as of July 2026) even though the top posted Ontario bracket says only 13.16%: with both surtax tiers, 13.16% × 1.56 is about 20.53% provincially, and adding the 33% federal top rate gives 53.53%.
Why you never see it
The surtax is computed on the ON428 provincial tax form, and it appears in no tax bracket table. As a result, bracket-based calculators, including many built on US-style logic, understate Ontario tax for anyone past the first threshold. Our Tax Calculator applies both tiers with the 2026 thresholds, which is why its Ontario results can look higher than a naive bracket lookup.
In Canada
The surtax was introduced in the 1990s as a deficit-fighting measure and was never removed. Prince Edward Island, the only other province still levying one in recent years, eliminated its surtax in 2024, which leaves Ontario's as the only provincial surtax in Canada (as of July 2026).
Worked example
Priya's Ontario basic tax for 2026 works out to $8,000. First tier: 20% of the amount above $5,818, so 20% × $2,182, about $436. Second tier: 36% of the amount above $7,446, so 36% × $554, about $199. Her surtax is roughly $636, bringing her Ontario tax to about $8,636. No line on her paycheque itemizes it; it simply arrives folded into the provincial tax she owes.
Related terms
Reviewed by Alexandre Bernier, CFP®, CIM®, PFP®·Updated July 2026