try
$future_timestamp = strtotime('+1 week', get_the_date('Y-m-d'));
echo date('Y-m-d', $future_timestamp);
or
$future_timestamp = get_the_date('U') + (60 * 60 * 24 * 7);
echo date('Y-m-d', $future_timestamp);
try
$future_timestamp = strtotime('+1 week', get_the_date('Y-m-d'));
echo date('Y-m-d', $future_timestamp);
or
$future_timestamp = get_the_date('U') + (60 * 60 * 24 * 7);
echo date('Y-m-d', $future_timestamp);