public function nthInstallmentDate($n = 1)
{
$date = $this->installmentGraceDate()->copy();
if ($this->loan->isWeeklyInstallment()) {
$date->addWeeks($n);
} else {
if ($date->day == 31) {
$date->firstOfMonth()->addMonths($n)->lastOfMonth();
} else {
$date->addMonths($n);
}
}
return $date;
}