var now = new Date(alertDate),
_3_months_from_now = new Date(now + 3*30*24*60*60*1000),
_6_months_from_now = new Date(now + 2*_3_months_from_now),
_2_year_from_now = new Date(now + 4*_6_months_from_now),
_5_year_from_now = new Date(now + 10*_6_months_from_now),
_5_sec_from_now = new Date(now + 5*1000);
Please refer the code how i was calculate the alertDate.
Sample date dateD = 01-25-2016
var Sdate = new Date(dateD);
var Rimyear = Sdate.getFullYear();
var Rimmonth = Sdate.getMonth();
var Rimdate = Sdate.getDate();
var storedDate = timeD;
var x = storedDate.substr(0,2); // x will have hours
var y = storedDate.substr(3,2); // y will have minutes
var z = storedDate.substr(6,2); // z will have meridian
if(z == 'PM'){
var xH = parseInt(x) + 12;
}else{
var xH = x;
}
//Convert the hours and minutes to number
var inputDate = new Date();
inputDate.setHours(xH);
inputDate.setMinutes(y);
var Rimhours = inputDate.getHours();
var Rimminutes = inputDate.getMinutes();
if(BeforeT != null){
if(BeforeO == 'min'){
var Bminute = BeforeT;
var delayDate = new Date(Rimyear,Rimmonth,Rimdate,Rimhours,Rimminutes,0).getTime();
var alertDate = new Date(delayDate - Bminute * 60 * 1000);
}else{
var Bminute = BeforeT;
var delayDate = new Date(Rimyear,Rimmonth,Rimdate,Rimhours,Rimminutes,0).getTime();
var alertDate = new Date(delayDate - Bminute * 60 * 60 * 1000);
}
}else{
var alertDate = new Date(Rimyear,Rimmonth,Rimdate,Rimhours,Rimminutes,0);
}