[Shamun]

Try using this:

{*
For http://forum.x-cart.com/showthread.php?t=53578

Call extra fields via this:
        {$extra_fields.0.field_value}
        {$extra_fields.1.field_value}
        {$extra_fields.2.field_value}
        

*}


{literal}
<script type="text/javascript">

var startyear = "1950";

var endyear = "2010";

var dat = new Date();

var curday = dat.getDate();

var curmon = dat.getMonth()+1;

var curyear = dat.getFullYear();

function checkleapyear(datea)

{

    if(datea.getYear()%4 == 0)

    {

        if(datea.getYear()% 10 != 0)

        {

            return true;

        }

        else

        {

            if(datea.getYear()% 400 == 0)

                return true;

            else

                return false;

        }

    }

return false;

}

function DaysInMonth(Y, M) {

    with (new Date(Y, M, 1, 12)) {

        setDate(0);

        return getDate();

    }

}

function datediff(date1, date2) {

    var y1 = date1.getFullYear(), m1 = date1.getMonth(), d1 = date1.getDate(),

     y2 = date2.getFullYear(), m2 = date2.getMonth(), d2 = date2.getDate();



    if (d1 < d2) {

        m1--;

        d1 += DaysInMonth(y2, m2);

    }

    if (m1 < m2) {

        y1--;

        m1 += 12;

    }

    return [y1 - y2, m1 - m2, d1 - d2];

}



function calage()

{
{/literal}
var calday = {$extra_fields.0.field_value};

var calmon = {$extra_fields.1.field_value};

var calyear = {$extra_fields.2.field_value};
{literal}
    if(curday == "" || curmon=="" || curyear=="" || calday=="" || calmon=="" || calyear=="")

    {

        alert("please fill all the values and click go -");

    }    

    else

    {

        var curd = new Date(curyear,curmon-1,curday);

        var cald = new Date(calyear,calmon-1,calday);

        

        var diff =  Date.UTC(curyear,curmon,curday,0,0,0) - Date.UTC(calyear,calmon,calday,0,0,0);



        var dife = datediff(curd,cald);

        document.birthday.age.value=dife[0]+" years, "+dife[1]+" months, and "+dife[2]+" days";

        var monleft = (dife[0]*12)+dife[1];

        var secleft = diff/1000/60;

        var hrsleft = secleft/60;

        var daysleft = hrsleft/24;

        document.birthday.months.value=monleft+" Month since your birth";    

        document.birthday.daa.value=daysleft+" days since your birth";    

        document.birthday.hours.value=hrsleft+" hours since your birth";

        document.birthday.min.value=secleft+" minutes since your birth";

        var as = parseInt(calyear)+dife[0]+1;

        var diff =  Date.UTC(as,calmon,calday,0,0,0) - Date.UTC(curyear,curmon,curday,0,0,0);

        var datee = diff/1000/60/60/24;

        document.birthday.nbday.value=datee+" days left for your next birthday";    





    }

}

$(document).ready(function(){

calage();
});


</script>
{/literal}



<form name="birthday">


<input name="age" size="40" value="Result"><br>
 </form>

It auto-calculates on page load, but it requires jquery (no worry, x-cart comes with it and will not have any issues :P) so importing into another program won't work later unless it uses jquery.