Decimal numbers are not stored as expected in mysql

When I want to store decimal numbers in mysql decimal field formatted like**(8,4), but it's not stored completely. ie **13850 is stored as 13.0000. This is my code in controller (Laravel):

$getRate = DB::table('currency_rates')
        ->select('crt_id','buy_rate')->orderBy('created_at','desc')->first();
        $rate = $getRate->buy_rate;
        $c_price = ($unit_price*$rate);
        $expense->c_price = number_format($c_price,4);
        $expense->c_total = number_format($quantity*$c_price,4);
//            dd(number_format($quantity*$c_price,4));
        $expense->rate_id = $getRate->crt_id;

Your help really appreciated.