How Taxes are calculated
First of all, I'm not an accountant, nor a tax specialist. This is also not a tax program so your options are limited to select one of three countries.
It's beyond the scope of this calculator to realize a full featured tax program. I don't include personal tax credits, deductions, allowances, carry overs..etc. All I do is use the publicly available tax schedules to calculate your basic FEDERAL income tax.
I know it's not ideal, but this is supposed to be an approximation. We will continue under the assumption that any credits, deductions, allowance etc, cancel out any Provincial or State income tax that you might owe.