Step One: Calculate Your After_Tax Income. Your after_tax income is what remains of your paycheck after taxes are taken out, such as state tax, local tax, income tax, Medicare, and Social Security. If you're an employee with a steady paycheck, your after_tax income should be easy to figure out. Look at your paystubs. If health care, retirement contributions, or any other deductions are taken out of your paycheck, add them back in.
If you're self_employed, your after_tax income equals your gross income less your business expenses, such as the cost of your laptop or airfare to conferences, as well as the amount you set aside for taxes. You're responsible for remitting your own quarterly estimated tax payments to the government because you don't have an employer to take care of it for you.