format your date to yyyy-MM-dd like this:
function Financialyear()
{
debugger;
var ModifyDate = Xrm.Page.getAttribute("modifiedon").getValue();
if(ModifyDate){
var year = ModifyDate.getFullYear();
var month;
var day;
if(dateFieldValue.getMonth()+1 < 10){
month = "0" + dateFieldValue.getMonth()+1;
}
else{
month = dateFieldValue.getMonth()+1;
}
if(dateFieldValue.getDate() < 10){
day = "0" + dateFieldValue.getDate();
}
else{
day = dateFieldValue.getDate();
}
var dateFormat = year + "-" + month + "-" + day;
}
var FecthXml = "<fetch version='1.0' output-format='xml-platform' mapping='logical' distinct='false'>" +
"<entity name='new_test'>" +
"<attribute name='new_testid'/>" +
" <attribute name='new_name'/>" +
"<attribute name='createdon'/>" +
"<attribute name='new_fromdate'/>" +
"<attribute name='new_todate'/>" +
"<order attribute='new_name' descending='false'/>" +
"<filter type='and'>" +
"<condition attribute='new_fromdate' operator='on-or-after' value='" + dateFormat + "' />" +
"</filter>" +
"</entity>" +
"</fetch>";
var RevenueRecords = XrmServiceToolkit.Soap.Fetch(FecthXml);
if (RevenueRecords.length > 0) {
alert("");
}
}