A $20/hour employee costs $24-28/hour. FICA, Medicare, FUTA, SUTA, workers' comp.
On top of every dollar of wage: FICA (6.2%), Medicare (1.45%), FUTA (~0.6%), SUTA (1.5-5%), and workers' compensation ($5-15 per $100 payroll). A $20/hour employee costs approximately $24-28/hour loaded. That loaded rate — not the base wage — goes into every estimate.