The self-assessment tax is the tax payable to net taxable income minus taxes already paid. To calculate the self-assessment tax first calculate the net taxable income after giving into effect every deduction and exemption. Now calculate the total tax payable on such net taxable income. Self-assessment tax will be total tax payable minus taxes already paid i.e. TDS/ TCS, advance tax, tax relief under section 87A/90/90A/91, tax credit, AMT/ MAT. You can also refer to Scripbox’s Income Tax Calculator to calculate the total tax payable on income earned.