Buongiorno a tutti, chi sa dirmi perchè il seguente codice non avvia lo script onload nonostante lo stesso funzioni benissimo onblur?

codice:
<html>
<head>

</head>

<script type="text/javascript">
function calcola_TOTAL(ff) {
  var OP = parseFloat(ff.operating.value);
  var LEG = parseFloat(ff.legal.value);
  ff.totalcostestimate.value = (OP+LEG);
}
</script>


<body onload="calcola_TOTAL(this.form);">

<form name="form1" method="post" action="" >
  <table border="0">
  
</table>
  <table border="0">
     <tr>
       <td>Operating</td>
       <td>
         <input name="operating" type="text" id="operating" size="15" value="3"  onblur="calcola_TOTAL(this.form);">
       </td>
     </tr>
     <tr>
       <td>Legal</td>
       <td>
         <input name="legal" type="text" id="legal" size="15" value="4"  onblur="calcola_TOTAL(this.form);">
       
	     <input name="financial" type="hidden" value="0"> 
	 </td>
     </tr>
     <tr>
       <td>TOTAL COST ESTIMATE </td>
       <td>
        
         <input name="totalcostestimate" type="text" id="totalcostestimate" size="15" style="background-color: #EBEBEB; font-size: 16px; font-weight: bold;" readonly> 
         </td>
     </tr>
   </table>
</form>

</body>
</html>
Grazie per l'interessamento,
AleX