[dollars-a-year] = [dollars-an-hour] × [hours-per-week] × [work-weeks-per-year] By default [hours-per-week] = 40 (5 days × 8 hours) and work weeks are 50 (52 weeks minus 2 weeks off each year as average unpaid vacation time)
$21 an hour to Annual Salary Conversion breakdown and explanation
To convert from hourly wage to annual salary you need to multiply the hourly wage in dollars by work hours in a week and then multiply it once again by the number of working weeks in a year. If you want to calculate the weekly wage you need to calculate the hourly wage by the number of working hours in a week.
So in this case annual salary is equal to: $21 × 40 × 50 = 840 × 50 = $42000 Weekly wage is equal to: $21 × 40 = $840