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.
Finally, do it again. After you have completed your first month of budgeting, it will be easier to plan for the next month. At the end of the month look at how you spent and make adjustments for categories in which you spent more than you planned, and cut back on the categories that had additional funds in them.