function calcPrice() {


	//get relevant data from form fields
	vanD=parseInt(document.boekform.data_DatumvanD.value,10); // ,10 argument to parse as decimal number
	vanM=parseInt(document.boekform.data_DatumvanM.value,10) - 1; //month starts at 0 with JS Date
	vanJ=parseInt(document.boekform.data_DatumvanJ.value,10);
	tmD=parseInt(document.boekform.data_DatumtmD.value,10);
	tmM=parseInt(document.boekform.data_DatumtmM.value,10) - 1;	
	tmJ=parseInt(document.boekform.data_DatumtmJ.value,10);
	aantV=parseInt(document.boekform.data_Aantvolw.value,10);
	aantK=parseInt(document.boekform.data_AantkindG.value,10);

	//assign price variables, depending on the year
	if (vanJ==2004) {
		dayPrice=55; // price per day
		dayPriceFullWeek=50; //discount per day if more than 6 days booked
	}else{
		dayPrice=60; //price per day
		dayPriceFullWeek=54; //discount per day if more than 6 days booked
	}	
	extCharge=3; // price per day for persons > 2
	
	//review data
	if(isNaN(aantK)) {aantK=0}

	if ((vanJ < 2000) && (vanJ>0)) {
		vanJ = vanJ+2000;
		document.boekform.data_DatumvanJ.value=vanJ;
	}
	if ((tmJ < 2000) && (tmJ>0)) {
		tmJ = tmJ+2000
		document.boekform.data_DatumtmJ.value=tmJ;	
	
	}
	
	if (document.boekform.data_Babybed.value=='J')
	{
		extBbed = 2;
	}
	else
	{
		extBbed = 0;
	}
	
	//create date variables and calculate number of days
	vanDatum = new Date(vanJ,vanM,vanD);
	tmDatum= new Date(tmJ,tmM,tmD);
	numDays=((tmDatum-vanDatum)/86400000); // 24*60*60*1000 (date calc gives milliseconds)
	numDays=numDays.toFixed(0); //some bug with date = 24-3-2006
	
	//calculate price, number of people and total
	if (numDays>6) {dayPrice=dayPriceFullWeek} // discount if more than 6 days booked
	numPersons=aantV+aantK;
	if (numPersons>2) {
		aantExt=(numPersons-2);
	}else{
		aantExt=0;
	}
	total=(numDays*dayPrice)+(aantExt*extCharge*numDays)+(numDays*extBbed);
	
	total=total.toFixed(2);
	if (!isNaN(total) && (total>0)) {
		document.boekform.data_Price.value=total;
	}else{
		document.boekform.data_Price.value='';
	}
}