Discretionary income is the amount of money remaining from her income after paying federal taxes, other mandatory charges, and necessary expenditures for living. In this situation, Emily is earning a gross income of $97,000. When you deduct her necessary expenditures for mortgage, food, and clothing in the amount of $37,000 and her federal income taxes in the amount of $24,000 from her gross income, you can get her discretionary income which is $36,000.