Converting timestamp to time ago in PHP e.g 1 day ago, 2 days ago...

$time_elapsed = timeAgo($time_ago); //The argument $time_ago is in timestamp (Y-m-d H:i:s)format.

//Function definition

function timeAgo($time_ago)
{
    $time_ago = strtotime($time_ago);
    $cur_time   = time();
    $time_elapsed   = $cur_time - $time_ago;
    $seconds    = $time_elapsed ;
    $minutes    = round($time_elapsed / 60 );
    $hours      = round($time_elapsed / 3600);
    $days       = round($time_elapsed / 86400 );
    $weeks      = round($time_elapsed / 604800);
    $months     = round($time_elapsed / 2600640 );
    $years      = round($time_elapsed / 31207680 );
    // Seconds
    if($seconds <= 60){
        return "just now";
    }
    //Minutes
    else if($minutes <=60){
        if($minutes==1){
            return "one minute ago";
        }
        else{
            return "$minutes minutes ago";
        }
    }
    //Hours
    else if($hours <=24){
        if($hours==1){
            return "an hour ago";
        }else{
            return "$hours hrs ago";
        }
    }
    //Days
    else if($days <= 7){
        if($days==1){
            return "yesterday";
        }else{
            return "$days days ago";
        }
    }
    //Weeks
    else if($weeks <= 4.3){
        if($weeks==1){
            return "a week ago";
        }else{
            return "$weeks weeks ago";
        }
    }
    //Months
    else if($months <=12){
        if($months==1){
            return "a month ago";
        }else{
            return "$months months ago";
        }
    }
    //Years
    else{
        if($years==1){
            return "one year ago";
        }else{
            return "$years years ago";
        }
    }
}

Use example :

echo time_elapsed_string('2013-05-01 00:22:35');
echo time_elapsed_string('@1367367755'); # timestamp input
echo time_elapsed_string('2013-05-01 00:22:35', true);

Input can be any supported date and time format.

Output :

4 months ago
4 months ago
4 months, 2 weeks, 3 days, 1 hour, 49 minutes, 15 seconds ago

Function :

function time_elapsed_string($datetime, $full = false) {
    $now = new DateTime;
    $ago = new DateTime($datetime);
    $diff = $now->diff($ago);

    $diff->w = floor($diff->d / 7);
    $diff->d -= $diff->w * 7;

    $string = array(
        'y' => 'year',
        'm' => 'month',
        'w' => 'week',
        'd' => 'day',
        'h' => 'hour',
        'i' => 'minute',
        's' => 'second',
    );
    foreach ($string as $k => &$v) {
        if ($diff->$k) {
            $v = $diff->$k . ' ' . $v . ($diff->$k > 1 ? 's' : '');
        } else {
            unset($string[$k]);
        }
    }

    if (!$full) $string = array_slice($string, 0, 1);
    return $string ? implode(', ', $string) . ' ago' : 'just now';
}

function time_elapsed_string($ptime)
{
    $etime = time() - $ptime;

    if ($etime < 1)
    {
        return '0 seconds';
    }

    $a = array( 365 * 24 * 60 * 60  =>  'year',
                 30 * 24 * 60 * 60  =>  'month',
                      24 * 60 * 60  =>  'day',
                           60 * 60  =>  'hour',
                                60  =>  'minute',
                                 1  =>  'second'
                );
    $a_plural = array( 'year'   => 'years',
                       'month'  => 'months',
                       'day'    => 'days',
                       'hour'   => 'hours',
                       'minute' => 'minutes',
                       'second' => 'seconds'
                );

    foreach ($a as $secs => $str)
    {
        $d = $etime / $secs;
        if ($d >= 1)
        {
            $r = round($d);
            return $r . ' ' . ($r > 1 ? $a_plural[$str] : $str) . ' ago';
        }
    }
}