Php Average Two Dates Based On Percentage

Question

I need to find the average birth date for a group of people. Say there are 5 people with the birth date of 5/14/2014 and 5 people with the birth date of 5/16/2014. The average would be 5/15/2014. I need a way to put this into a function.

The function needs to be able to handle things like 10 people born on 5/14/2014 and 50 people born on 5/18/2014. This would obviously average around 5/17/2014.

I'm thinking I could do something like this.

//date1 and date2 are the dates given
//total1 and total2 are the number of people for each date 
$time1 = strtotime($date1);
$time2 = strtotime($date2);
$total = ($time1 * $total1) + ($time2 * $total2);
$avg = $total / ($total1 + $total2);
$final = date("Y-m-d",$avg);

Answer 1

Just takes the dates, turn them into timestamps, add them up, divide by the number of birthdays, and the print out the date of that final timestamp.

$birthdays = array('2014-05-14','2014-05-15','2014-05-16','2014-05-17','2014-05-18');
$total_timstamp = 0;
foreach ($birthdays as $birthday) {
    $total_timstamp = bcadd($total_timstamp, (new DateTime($birthday))->format('U'));
}
$average_timestamp = bcdiv($total_timstamp, count($birthdays));
echo date('Y-m-d', $average_timestamp);

Demo

This should also work with dates in MM/DD/YYYY format.