US pay guide
How a W-4 affects your take-home pay
Form W-4 tells an employer how much federal income tax to withhold. It affects your payslip, but it does not by itself change your final tax bill.
In short
More withholding generally means lower take-home pay now and may mean a larger refund later. Too little withholding can leave tax to pay when you file.
What a W-4 changes
Your filing status, multiple-job adjustment, dependent credits, other income, deductions and any extra withholding can alter federal payroll withholding.
Why estimates can differ
A salary calculator uses standard assumptions. Your employer applies your actual W-4 and pay-period payroll method, so the federal income-tax line on a payslip can differ even when salary is the same.
When to review it
Consider reviewing your W-4 after starting a new job, changing marital status, adding a job, having a child, or seeing a large unexpected balance due or refund.
Use the US take-home pay calculator as a baseline. The IRS Form W-4 guidance explains the official form.