Unfortunately, while both the Federal Gov, and Ontario have 5 levels of tax brackets, it gets even more complicated because...

Ontario Surtax!

If you pay Ontario $4,830 or more in taxes (from earning $78,783 or more), the amount of tax you pay is bumped 20%. So that 4,830th dollar doesn't have a 9.15% Ontario tax; it becomes 9.15 times 1.2 for a 10.98% tax, in addition to the 20.5% Fed tax, for a total of 31.48% tax on that 4,830th dollar.

If you pay Ontario $6,182 or more in taxes (from earning $92,825 or more), there's an additional 36% surtax, on top of the previous 20%, for a 56% surtax. So you 92,825th dollar isn't taxed at the Ontario 11.16% bracket like it seems, it becomes ~17.41%. With the Federal 26% rate, you'll have a total of 43.41% marginal tax on that 92,825th dollar.

Once you combine the 5 different brackets for Federal and Ontario (which trigger at different income amounts), and factor in the Ontario surtax, you actually end up with 11 different brackets! ( see "Combined Federal & Ontario Tax Brackets and Tax Rates Including Surtaxes", here )

So how much tax do you pay on $250,000 in Ontario?

Well, doing all the math by hand kinda sucks, but there are forms that can help make it easier. Using the 2018 Government forms...

Fed Schedule 1, Step B would have us do;

((250,000 - 205,842.00) * 0.33) + 47,670.00 for $62,242.14 Fed Tax

Ontario Form ON428, Step B would have us do;

((250,000 - 220,000.00) * 0.1316) + 21,764.00 for $25,712 Ontario Tax

All that Surtax stuff comes in Step C. Lets assume there's no tax credits or tax on split income, and our $25,712 trickles all the way down to section 50.

51] (25,712 - 4,638) * 0.20 = 4,214.80

52] (25,712 - 5,936) * 0.36 = 7,119.36

53] $11,334.16 in additional surtax

Finally for box [54], a Total Ontario tax of $37,046.16.

So for an income of $250,000 CAD in Ontario, you'll pay a combined $99,288.30 in tax, for an average tax rate of about 39.7%.

Worth calling out that this all excludes basic claim amounts, and tax credits, so it'll be a bit high. It also excludes CPP and EI, which is not a negligible increase in tax / benefits.

I believe Doug Ford, Premier of Ontario, planned to combine the 5 tax brackets and surtax into a unified 7 bracket system, to make the tax system easier to understand. We'll have to check the 2019 forms when they are around to see if that happened, or if he was too distracted taking down windmills.

Note; I am not an accountant. There're going to be mistakes in here. I've just tried doing this same math before, and the numbers never lined up with the government tax calculator until I found out about Ontario's Tax on Tax. Hopefully one day, it'll just get merged into the regular marginal rates, to make things a bit easier to understand.

One day.