Calculate your take-home pay (net pay) for the following situation. Gross Salary: $3,500 per month. You are paid once a month. Federal Income Tax Withholding = 20% of Gross Salary. State Income Tax Withholding = 12% of Gross Salary. Social Security Tax Withholding = 8.25% of Gross Salary. 401k Contribution = 4% of Gross Salary.