Count days and stop count if status is completed

I am trying to count the number of days between two dates and when the status == complete the count of days stops.

if ($this->status == 'COMPLETED') {
    $now = Carbon::now();
    $start_date = Carbon::createFromFormat('Y-m-d', $this->start_date);
    $this->start_date_to_current_date = $start_date->diffInDays($now, true);
}

But the problem is, the days still continues to count and increment. how can I can make the counting stop ?

via Chebli Mohamed