It would be tempting to just multiply by 4, which is the "standard" number of weeks in a month, right? Well, you'd get a very rough approximation. A better (more accurate) way is to:

1. Multiply your weekly wage by 52 (the number of weeks in a year), and then
2. Divide the result by 12 (the number of months in a year).

This is the formula implemented in most of online monthly salary calculators.

Your monthly income is $3,120, provided that you work 40 hours per week. Otherwise, you need to use the formula: monthly income = hourly wage × hours worked per week × 52/12 or resort to an online monthly income calculator.

This is a very simple conversion! You only need to divide your annual salary by 12 to obtain your monthly income. In other words, the conversion formula reads monthly = yearly/12.