<script type="text/javascript">
function faturaHesapla() {
var fiyat = document.getElementById("fyt").value;
var kdv = document.getElementById("kdv").value;
var toplam = fiyat*(kdv/100);
document.getElementById("sonFiyat").value = toplam;
}
</script>

<form name="genelForm">
<input id="fyt" type="text" onkeyup="faturaHesapla(); "name="fiyat" size="10" value="12000">KDV Hariç Fiyat<br />
<input id="kdv" type="text" onkeyup="faturaHesapla();" name="kdv" size="10" value="18" > KDV %olarak<br />
<input id="sonFiyat" type="text"onkeyup="faturaHesapla(); "name="toplam" size="10"> Son Fiyat<br />
</form>
[COLOR=#000000][FONT=Open Sans][SIZE=2][/SIZE][/FONT][/COLOR]