<?php
$data1 = '20-09-2016';
$data2 = '23-09-2016';
echo ( $dia2 - $dia1 ) / 86400;
PD9waHAKCiAgICAkZGF0YTEgPSAnMjAtMDktMjAxNic7CiAgICAkZGF0YTIgPSAnMjMtMDktMjAxNic7CgogICAgJGRpYTE9c3RydG90aW1lKCAkZGF0YTEgKTsKICAgICRkaWEyPXN0cnRvdGltZSggJGRhdGEyICk7CgogICAgZWNobyAoICRkaWEyIC0gJGRpYTEgKSAvIDg2NDAwOw==