Now that you know your annual gross income, divide it by 12 to find the monthly amount. Note: If your hours vary week to week, use your best estimate of the average number of hours you work. For example, if you are paid $12 per hour and work 40 hours per week, your weekly gross pay is $480. Multiplying this by 52 shows an annual gross income of $24,960. Finally, dividing by 12 reveals a gross income of $2,080 per month.