Even if this is already answered (1 year ago) you could also let the fields be calculated automatically.
The HTML
<tr>
<td><input type="text" value="" ></td>
<td><input type="text" class="class_name" placeholder="bla bla"/></td>
</tr>
<tr>
<td><input type="text" value="" ></td>
<td><input type="text" class="class_name" placeholder="bla bla."/></td>
</tr>
The script
$(document).ready(function(){
$(".class_name").each(function(){
$(this).keyup(function(){
calculateSum()
;})
;})
;}
);
function calculateSum(){
var sum=0;
$(".class_name").each(function(){
if(!isNaN(this.value) && this.value.length!=0){
sum+=parseFloat(this.value);
}
else if(isNaN(this.value)) {
alert("Maybe an alert if they type , instead of .");
}
}
);
$("#sum").html(sum.toFixed(2));
}