$date + 1 year?

$futureDate=date('Y-m-d', strtotime('+1 year'));

$futureDate is one year from now!

$futureDate=date('Y-m-d', strtotime('+1 year', strtotime($startDate)) );

$futureDate is one year from $startDate!

To add one year to todays date use the following:

$oneYearOn = date('Y-m-d',strtotime(date("Y-m-d", mktime()) . " + 365 day"));

For the other examples you must initialize $StartingDate with a timestamp value for example:

$StartingDate = mktime();  // todays date as a timestamp

Try this

$newEndingDate = date("Y-m-d", strtotime(date("Y-m-d", strtotime($StaringDate)) . " + 365 day"));

or

$newEndingDate = date("Y-m-d", strtotime(date("Y-m-d", strtotime($StaringDate)) . " + 1 year"));