Use objetos DateTime () e DateInterval () para Php 5.3 e acima e calcule a diferença entre duas datas usando PHP

phpCopy$firstDate  = new DateTime("2019-01-01");
$secondDate = new DateTime("2020-03-04");
$intvl = $firstDate->diff($secondDate);

echo $intvl->y . " year, " . $intvl->m." months and ".$intvl->d." day"; 
echo "\n";
// Total amount of days
echo $intvl->days . " days ";

//output: 1 year, 2 months and 1 day
//        428 days
CodeGuruDev