Count group by in laravel

My current select statement:

return User::select('id', 'created_at')
                    ->orderBy('created_at', 'desc')
                    ->get()
                    ->groupBy(function($date) {
                        return Carbon::parse($date->created_at)->format('Y m d');
                    });

This currently returns

2015 07 28: [
{
id: 935,
created_at: "2015-07-28 23:00:20"
}
],

2015 07 27: [
{
id: 926,
created_at: "2015-07-27 17:13:58"
},
{
id: 925,
created_at: "2015-07-27 15:00:36"
},
{
id: 924,
created_at: "2015-07-27 13:37:00"
}
]

What I just want is:

Date | Users
-----+------
7/28 | 1
7/27 | 3