Form field with multiple if statements

Good morning all , the issue im having with this script is that Annual income is only calculating when B is populated, otherwise if "b" is blank and "c" or "d" is populated nothing happens. 

The correct operator is not:

=>

But:

>=

You need to state the specific issue when posting the question.  Otherwise we have to guess. 

The code looks good, So I'm assuming you're asking about how to incorporate "a" being empty?

The answer is, add a final else. 

var a = Number(this.getField("PayRate").valueAsString);
var b = Number(this.getField("HoursPerWeek").valueAsString);
var c = Number(this.getField("WeeksPerYear").valueAsString);
var d = Number(this.getField("MonthsPerYear").valueAsString);
if (b=>0)
{event.value = a*b ;}
else if (c=>0)
{event.value = a*c ;}
else if (d=>0)
{event.value = a*d ;}
else
   event.value = 0;

If you want the Anual income field to be blank when the calculatin is zero, then put that in the formatting.