php strtotime plus 1 day

// add 1 day to the date above
$n = date('Y-m-d', strtotime( $d . " +1 days"));

// add 1 month to the date above
$n = date('Y-m-d', strtotime( $d . " +1 month"));

// add 1 year to the date above
$n = date('Y-m-d', strtotime( $d . " +1 year"));

// subtract 1 day to the date above
$n = date('Y-m-d', strtotime( $d . " -1 days"));

// subtract 1 month to the date above
$n = date('Y-m-d', strtotime( $d . " -1 month"));

// subtract 1 year to the date above
$n = date('Y-m-d', strtotime( $d . " -1 year"));

$NewDate = date('Y-m-d', strtotime('+7 days'));