Date picker selection change

Question

I have two Datepicker named datepicker1 and datepicker2 .I have a textbox also.datepicker1 shows the current date and datepicker2 shows a date of six monthes later from now.I want to show the difference in monthes in the textbox when i put the date in the datepicker2.How can i implement this on selection change event using the datepicker2.plz help me.Thanks in advance.