function calc() {
	var price   = parseInt( no_commas( document.stampduty.price.value ) );
	if( isNaN( price ) ) {
		alert('Please enter the purchase price using only numbers and commas');
	} else {
		var factor;
		if( price <= 125000 ) {
			factor = 0;
		} else if( price <= 250000 ) {
			factor = 1;
		} else if( price <= 500000 ) {
			factor = 3;
		} else {
			factor = 4;
		}
		var duty =  Math.round( ( price * factor ) / 100 );
		var dstr = duty.toString();
		var nice = '';
		var nc = 0;
		for (i = dstr.length - 1; i > 0; i-- ) {
			if (nc == 3) {
				nice = ',' + nice;
				nc = 0;
			}
			nice = dstr.charAt(i) + nice;
			nc++;
 		}
		if (nc == 3) {
			nice = ',' + nice;
		}
		nice = dstr.charAt(0) + nice;
		document.stampduty.duty.value =  nice;
	}
}

function no_commas( value ){
	return( value.replace( /,/g, "" ) );
}