Start with gross salary
Gross salary is the headline number in your offer letter or annual compensation summary. It is the amount before federal income tax, payroll taxes, and most payroll deductions. The problem is that gross salary is not the number you can budget with. What matters for rent, groceries, debt payments, and investing is the net amount left after tax and deductions.
Subtract pre-tax deductions first
Many payroll items come out before income tax is calculated. Common examples are 401(k) contributions, HSA contributions, and some insurance premiums. These deductions reduce the wage base that federal and state income taxes are applied to. They do not always reduce every tax equally, so payroll systems can still look more complicated than a simple calculator.
Federal income tax uses brackets, not one flat rate
A lot of weak salary calculators pretend federal tax is one flat percentage. That is not how federal income tax works. The United States uses marginal tax brackets. That means one slice of income is taxed at 10%, another slice at 12%, another at 22%, and so on. Your filing status also matters because it changes the bracket thresholds and the standard deduction.
FICA is separate from federal income tax
On most W-2 wages, Social Security and Medicare are separate payroll taxes. Social Security applies up to the annual wage base, while Medicare applies to all wages and can increase for higher earners. This is one reason a paycheck can feel smaller than expected even in a state with no wage income tax.
State tax can be zero, flat, or progressive
Some states do not tax wage income at all. Others use a flat tax rate, while others use progressive brackets. That means the same salary can produce meaningfully different take-home pay depending on where you live and work. In some places local taxes can also matter, which is why editable state and local inputs are useful.
Why paycheck estimates still differ from pay stubs
Even a solid take-home calculator is still an estimate. Your Form W-4, extra withholding, tax credits, bonuses, commuter deductions, health insurance, and retirement contributions all change the final paycheck. A good calculator gets you directionally close. Your pay stub tells you the exact payroll treatment your employer is using.