Calculadora de Hipotecas (Años=Meses)

[creear]

Hola, tengo esta calculadora de hipotecas, que me permite ingresar los años, si quisiera que en vez de años sean meses, que debo modificar?

PD: Nunca me llevé bien con cálculo financiero ni JacaScript

Código:

<table align="center" border="0" cellpadding="2" cellspacing="0" width="506">
  <tbody><tr> 
    <td width="502" valign="top">
      <form action="POST" name="myform"> <table bgcolor="#666" border="0"> 
  <tbody><tr> <td width="304" height="81" colspan="2" align="center"> <script language="JavaScript"><!--
function Morgcal()
{
	form = document.myform
	LoanAmount= form.LoanAmount.value
		
	DownPayment= "0"
	AnnualInterestRate = form.InterestRate.value/100
	Years= form.NumberOfYears.value
		MonthRate=AnnualInterestRate/12
	NumPayments=Years*12
	Prin=LoanAmount-DownPayment
	
	MonthPayment=Math.floor((Prin*MonthRate)/(1-Math.pow((1+MonthRate),(-1*NumPayments)))*100)/100
		form.NumberOfPayments.value=NumPayments
	form.MonthlyPayment.value=MonthPayment
}
        // --></script> <font color="#FFFFFF" face="arial narrow" size="4"><b>Calculador de Hipotecas</b> 
  </font><br>Ingrese y decida sus condiciones</td></tr> <tr> 
  <td> <table width="357" border="0" cellpadding="2"> <tbody><tr> <td width="130" align="right"><font color="#FFFFFF" face="arial narrow" size="2">Monto del crédito en USD</font></td><td width="79"><font color="#FFFFFF" face="arial narrow" size="2"> <input size="10" name="LoanAmount" value="0" onBlur="Morgcal()" onChange="Morgcal()" type="text"> <br> </font></td></tr> 
  <tr> <td align="right"><font color="#FFFFFF" face="arial narrow" size="2">Tasa anual fija</font></td><td><font color="#FFFFFF" face="arial narrow" size="2"> <input name="InterestRate" type="text" disabled onBlur="Morgcal()" onChange="Morgcal()" value="18.0" size="3"> % <br> </font></td></tr> 
  <tr> <td align="right"><font color="#FFFFFF" face="arial narrow" size="2">Plazo del cr&eacute;dito</font></td><td><font color="#FFFFFF" face="arial narrow" size="2"> <input size="3" name="NumberOfYears" value="12" onBlur="Morgcal()" onChange="Morgcal()" type="text">
         A&ntilde;os<br> </font></td><td width="75"><font color="#FFFFFF" face="arial narrow" size="2"> <input name="morgcal" value="Calcular" language="JavaScript" onClick="Morgcal()" type="button"> </font></td></tr> 
  <tr> <td colspan="3"><font color="#FFFFFF"></font></td></tr> </tbody></table></td></tr> 
  <tr> <td> <table width="336" border="0" cellpadding="2"> <tbody><tr> <td width="137" align="right"><font color="#FFFFFF" size="2">Cantidad de cuotas</font></td><td width="153"><font color="#FFFFFF" face="arial narrow" size="2"> <input name="NumberOfPayments" type="text" disabled value="0" size="7"> <br> </font></td></tr> <tr> 
  <td align="right"><font color="#FFFFFF" face="arial narrow" size="2">Cuota mensual USD</font></td><td><font color="#FFFFFF" face="arial narrow" size="2"> <input name="MonthlyPayment" type="text" disabled value="0" size="7"><br> </font></td></tr>
          <tr>
            <td align="right">&nbsp;</td>
            <td>&nbsp;</td>
          </tr>
  </tbody>
  </table></td></tr> </tbody></table></form></td>
</tr> </tbody></table>