Ontario has more tax layers than any other province. The combination of a five-bracket progressive income tax, a two-tier surtax, a Health Premium, and several income-tested credits creates a complex after-tax picture that materially affects support calculations. A payor earning $150,000 in Ontario faces a significantly different effective tax rate — and therefore a different NDI — than the same income in Alberta or British Columbia.

Ontario Tax Brackets (2025)

The Ontario Surtax

On top of the bracket rates, Ontario applies a two-tier surtax on the basic provincial tax amount (after non-refundable credits):

At the second tier, the combined surtax rate is effectively 56% on the incremental provincial tax. This means that for high-income earners, the effective provincial rate is substantially higher than the statutory 13.16% top bracket suggests. The surtax is a tax on tax, not on income — which makes it particularly opaque to people trying to estimate their after-tax position manually.

Ontario Health Premium

The Ontario Health Premium is an additional charge on taxable income above $20,000, ranging from $0 to a maximum of $900 per year. It is not technically a tax (it is not deducted at source and does not appear on the T4), but it functions as one for the purpose of determining after-tax income and NDI. The premium is calculated on a sliding scale with six income tiers and is added directly to provincial tax payable.

Ontario Benefits

Ontario offers several income-tested benefits that enter the NDI waterfall:

For a lower-income parent with two children, the OCB alone can add over $3,400 per year to their NDI — a significant factor in the spousal support analysis.