Need to Create a Custom Calculation Script

You can use this code as the custom calcualtion script of the amount field:

var startDateString = this.getField("Start Date").valueAsString;
var endDateString = this.getField("End Date").valueAsString;
if (startDateString=="" || endDateString=="") event.value = "";
else {
	var d1 = util.scand("m/d/yy", startDateString);
	var d2 = util.scand("m/d/yy", endDateString);
	var diffInDays = Math.round((d2.getTime()-d1.getTime())/86400000);
	event.value = diffInDays*200;
}

Why is the result 3, in this case? Does it not include the first day? What should happen if both dates are the same?

You can accomplish this by creating your own script with Acrobat JavaScript. Have you tried doing your own script?

If so, would you mind sharing it?

In the meanwhile, see this tutorial from ACP Thom Parker on how to calculate the total number of days based on two dates: 

• Working with date and time in Acrobat JavaScript - PART 1 
• Working with date and time in Acrobat JavaScript - PART 2 
• Working with date and time in Acrobat JavaScript - PART 3 

Check the sections that explain how to calculatethe difference in  total number of days. Then add to your script a conditional statement to calculate the total number of days obtained from the two dates and multiply by the desired dollar anount or by obtaining the value from another field object in your PDF form.