Storing result after each iteration

I have an iteration that runs for a set number of times depending on another value which can vary which is why I'm using an iteration that iterates based on that value, inside that iteration I add 30 days to a date once each iteration and then add the results to a table.

PROBLEMS

I simply end up with the first instance of adding 30 days which is outside the iteration itself. This means that my values inside the iteration are not being stored properly but I can't see why.

I've checked the DateTime operations and displayed the value of newdate and it shows the proper date so it's most likely the storing of the date. But I don't know what's going wrong, it works pre-iteration which is what's got me confused. Why isn't it executing inside the iteration? Does anyone have any idea?

Ex.

InitialDate | 3/29/2015
2ndDate     | 4/28/2015<-- This is what's stored which is pre-iteration
3rdDate     | 5/28/2015<-- This is what it's supposed to be after the iteration
so on and so forth....

Values pre-iteration

    //Date stuff
    String startdate = (String.valueOf(Acc._date));
    DateTimeFormatter formatter = DateTimeFormat.forPattern("MM-dd-yyyy HH:mm:ss");
    DateTime dt = formatter.parseDateTime(startdate);
    DateTime startpoint = new DateTime(dt);
    DateTime whendue = startpoint.plusDays(30);
    DateTime foriteration = whendue;
    String formattedDate = whendue.toString(formatter);

    //Storing initial date
    pay.setDateDue(formattedDate);
    db.AddPayment(pay);

Actual iteration

    while (i < j) {

            //Operation for Date Calculation
            DateTime ndt = foriteration.plusDays(30);
            foriteration = ndt;
            String newdate = ndt.toString(formatter);

            //Adding values to PayTable
            pay.setDateDue(newdate);
            db.AddPayment(pay);

            i++;
    }