What it is
Employer relocation money is taxable income for most moves after 2018. A gross-up adds enough to cover the federal, state, and payroll tax on the payment, and the multiplier depends on the rate applied and the state line. Reimbursement with receipts is taxed differently than a lump grant.
What to do about it: Ask for the gross-up formula, not the net number. The state line you move to changes the multiplier, and the receipts route changes the taxable amount.
Plain-language description of US practice, not legal, tax, or financial advice. The paired guide carries the citations, dates, and thresholds; the state pages carry the local windows.