Check Date Between Two Dates in PHP

function dateBetween( $checkDate )
{
$firstDate1 = strtotime( "15-Jan-2008" );
$firstDate2 = strtotime( "15-Mar-2008" );
$secondDate1 = strtotime( "16-Mar-2008" );
$secondDate2 = strtotime( "15-Jun-2008" );

$checkDate = strtotime( $checkDate );

if( $checkDate > $firstDate1 && $checkDate < $firstDate2 )
{
return "2000";
}
elseif( $checkDate > $secondDate1 && $checkDate < $secondDate2 )
{
return "4000";
}

return "0";
}

echo dateBetween( "25-Sep-2008" );

?>