Net profit is revenue minus expenses. Self-employment tax is net profit times 0.9235 times 15.3%. Income tax is the federal percent you enter, applied to profit after half of the self-employment tax is removed. The year is then divided by four to suggest a quarterly amount.
Revenue of $100,000 and expenses of $20,000 leave $80,000 of profit. Self-employment tax is $11,303.64. At a 15% federal rate, income tax is $11,152.23. The four payments are $5,613.97 each.
This is a United States self-employment estimate. It is not a CRA instalment. It does not apply the qualified business income deduction, state tax, or the additional Medicare tax beyond the 15.3% self-employment rate used here.