PHP日期计算器返回错误的日子

Question

我正在使用下面的计算器来确定设定日期和当前日期之间的年，月和日。我以为它可以正常工作，但是后来又升到了年关，我注意到它工作不正常。明天实际上是一年的标记，但现在正在回归11 months, 34 days。谁能告诉我怎么了？应该是11 months, 30 days。function relationshipTimer($functionDate){    $date1 = $functionDate;    $date2 = date("Y-m-d");    $diff = abs(strtotime($date2) - strtotime($date1));    $years = floor($diff / (365 * 60 * 60 * 24));    $months = floor(($diff - ($years * 365 * 60 * 60 * 24)) / ((365 * 60 * 60 * 24) / 12));    $days = floor(($diff - $years * 365 * 60 * 60 * 24 - $months * 30 * 60 * 60 * 24) / (60 * 60 * 24));    if ($years > 0) {echo $years . " Year";}    if ($years > 1) {echo "s ";}    if ($months > 0) {echo " " . $months . " Month";}    if ($months > 1) {echo "s ";}    if ($date1 == $date2) {echo "1 Day ";}    if ($days > 0) {echo $days . " Day";}    if ($days > 1) {echo "s ";}}这是$ functionDate的来源：relationshipTimer("2018-04-28");