Configure and update employee W-4 federal tax withholding elections via a payroll API

Steps

1. Retrieve the employee's current W-4 withholding information from the Gusto federal tax details endpoint to confirm the current filing status, number of allowances (pre-2020 form) or withholding adjustments (2020+ form).
2. Accept the employee's new W-4 data: for 2020+ forms, capture filing status, amounts from Steps 3 and 4 (dependents, other income, deductions), and any additional withholding amount.
3. Submit the updated W-4 data via PUT or POST to the Gusto employee federal tax withholding endpoint with the new values and the date the employee signed the form.
4. Confirm the update is reflected in the employee's record before the next payroll processing deadline — changes submitted after the payroll lock date take effect in the following period.
5. Do not submit withholding elections that the employee did not authorize; retain the signed W-4 form for IRS record-keeping purposes (generally until 4 years after the tax becomes due or is paid).