function calculate date (validation date)

[sitie_aniem]

i have create a function to calculate date. whenever i enter it to the system, there having extra date. why get like that. the coding is just like the below.

function calculateDate(value)
{
	if (document.form.fromDate.value != null && value != null)
	{
		var date = getDate(document.form.fromDate.value);
	  	date.setDate(date.getDate() + parseInt(value)-1);
		
		var curr_date = date.getDate();
 		var curr_month = date.getMonth()+ 1;
		var curr_year = date.getFullYear();
		
		var dateString = formatString(curr_date) + "-" + formatString(curr_month) + "-" + curr_year;
		document.form.toDate.value= dateString;
 	}
}

function calculateValidDays()
{
	if (document.form.fromDate.value != null && document.form.toDate.value != null)
	{
		var fromDate = getDate(document.form.fromDate.value);
		var toDate = getDate(document.form.toDate.value);
		var date = new Date();
		date.setTime(Math.abs(fromDate.getTime() - toDate.getTime()));
	 	 
		days = Math.floor(date.getTime() / (1000 * 60 * 60 * 24)); 
	 
		document.form.days.value= days+1;
	}
	else if(document.form.toDate.value != null && document.form.days.value != "")
	{
		var date = getDate(document.form.toDate.value);
		date.setDate(date.getDate() - parseInt(document.form.days.value));
		
		var curr_date = date.getDate();
 		var curr_month = date.getMonth()+ 1;
		var curr_year = date.getFullYear();
		
		var dateString = formatString(curr_date) + "-" + formatString(curr_month) + "-" + curr_year;
		document.form.fromDate.value= dateString;
	}
	else if(document.form.fromDate.value != null && document.form.days.value != "")
	{
		var date = getDate(document.form.fromDate.value);
		date.setDate(date.getDate() + parseInt(document.form.days.value)+1);
		var curr_date = date.getDate();
 		var curr_month = date.getMonth()+ 1;
		var curr_year = date.getFullYear();
		
		var dateString = formatString(curr_date) + "-" + formatString(curr_month) + "-" + curr_year;
		document.form.toDate.value= dateString;
	}
}