The direct deposit hits your account and most people move on. The pay stub sitting in the HR portal contains a complete picture of where your labor compensation actually goes — but it requires knowing how to read it.
Gross Pay: The Starting Point
Gross pay is your total earnings before anything is withheld. For salaried employees, it is your annual salary divided by pay periods (typically 26 for biweekly, 24 for semimonthly, 12 for monthly). For hourly employees, it is hours worked times hourly rate, plus any overtime.
This is the number your employer reports to the IRS. It is not what you receive, but it is the starting point for understanding everything else on the stub.
Federal Income Tax: Your Withholding vs Your Actual Rate
Federal income tax withholding is an estimate, not your actual tax liability. Your employer calculates it based on the information you provided on your W-4 — your filing status, dependents, and any additional withholding you requested.
The amount withheld may be more or less than what you actually owe, which is why refunds and underpayment situations both occur. A large refund means you gave the government an interest-free loan during the year. A large underpayment bill means your withholding was insufficient.
Your marginal tax rate — the rate on your last dollar of income — is different from your effective rate — total tax paid divided by total income. Someone in the 22% marginal bracket does not pay 22% on all their income. They pay 10% on the first bracket of income, 12% on the next bracket, and 22% only on the portion that falls into the 22% bracket. Effective rates are almost always lower than marginal rates.
FICA: The Two Lines Labeled Social Security and Medicare
FICA taxes fund Social Security and Medicare. Employees pay 6.2% of wages for Social Security (on wages up to $176,100 in 2025, which is the wage base limit) and 1.45% for Medicare on all wages. Employers match these amounts.
High earners pay an additional 0.9% Medicare surtax on wages above $200,000 (single) or $250,000 (married filing jointly). Employers do not match this additional amount.
FICA is withheld separately from income tax and is non-negotiable — it cannot be adjusted through W-4 elections. Combined, employee FICA is 7.65% of wages up to the Social Security wage base, then 1.45% above it. For a worker earning $65,000, that is roughly $4,972 per year in FICA taxes.
Pre-Tax Deductions: What Lowers Your Taxable Income
Pre-tax deductions are subtracted from gross pay before federal income tax is calculated. They reduce your taxable income and therefore your income tax. 401k contributions, health insurance premiums (for employer-sponsored plans under Section 125), FSA contributions, HSA contributions, and some other benefit deductions fall into this category.
This matters more than most people realize. A $500 per month 401k contribution does not reduce your take-home pay by $500. It reduces it by $500 minus the income tax you would have paid on that $500. For someone in the 22% federal bracket in a state with 5% income tax, each $500 contributed to a 401k only costs about $365 in take-home pay reduction — the rest offsets taxes you would otherwise owe.
Health insurance premiums deducted pre-tax also reduce FICA in some cases, not just income tax, depending on how the plan is structured.
The Four Numbers Worth Calculating
Most people look at gross and net. Four additional calculations from your pay stub tell you significantly more:
Your effective tax rate. Total taxes withheld (federal + state + local income taxes — not FICA) divided by gross pay. This is your actual income tax burden, not your marginal rate.
Your total withholding percentage. All deductions — including FICA, health insurance, 401k, and all taxes — divided by gross pay. This tells you the full gap between your gross and net and what is causing it.
Your employer's total cost per pay period. Your gross pay plus the employer's FICA match (another 7.65%) plus their portion of health insurance and other benefits. This is your true total compensation, which is often 20–30% higher than your salary suggests.
Year-to-date totals. Every pay stub shows year-to-date figures in addition to current period figures. YTD columns tell you whether you are on track with estimated taxes and where you stand relative to contribution limits. If your YTD 401k contributions are approaching the annual limit, you may need to adjust your contribution rate to avoid stopping contributions partway through the year.
When to Update Your W-4
The W-4 determines your withholding. You should revisit it when your situation changes: marriage, divorce, a new child, a second job, significant investment income, or a major salary change. The IRS has an online withholding estimator that helps you determine the right settings based on your full expected income for the year.
Neither a large refund nor a large bill is inherently good or bad — but understanding why either is happening is worth the few minutes it takes to read the full pay stub.