Model your exact net deposit per pay period with pre-tax deductions like 401(k), HSA, and health insurance, plus post-tax deductions like student loans and child support.
Pre-tax deductions like 401(k) contributions, HSA contributions, and employer-sponsored health insurance premiums are subtracted from your gross income before federal and state income taxes are calculated. This means every dollar you contribute pre-tax reduces your taxable income and saves you money at your marginal tax rate. However, FICA taxes (Social Security and Medicare) are still calculated on your full gross salary regardless of pre-tax deductions.
Pay frequency affects your per-paycheck amount in ways that may surprise you. If you are paid biweekly (26 paychecks), you receive two "extra" paychecks per year compared to semi-monthly (24 paychecks). While your annual net pay is identical, biweekly paychecks are smaller individually but you get two months per year with three paychecks, which can help with budgeting and savings goals.
Your 401(k) contributions generate tax savings at your marginal federal tax rate. For example, if you are in the 22% federal bracket and contribute $500 per paycheck to your 401(k), you save approximately $110 per paycheck in federal income tax alone, plus additional state tax savings in most states. The true cost of a $500 contribution is closer to $350-$390 depending on your state.
Post-tax deductions like student loan payments, child support, and garnishments are taken from your paycheck after all taxes have been calculated. They do not reduce your federal, state, or FICA tax liability. They simply reduce the net deposit that lands in your bank account. Understanding the distinction between pre-tax and post-tax deductions is key to optimizing your paycheck.