PHP Calculation

I have a form based program featured a Total Deductions value that is calculating fine and looks like this:

echo $str.='<tr class="style14" height=30 style4><td colspan=2>Total Deductions:</td><td colspan=2>$'.number_format($Section179Amount+$BonusDepAmount+$fyearvalue, 2, '.', ',').'</td></tr>';

I want to also provide this value in a % of total cost and changed the echo statement to look like this to incorporate a percent value:

$percent = (number_format($Section179Amount+$BonusDepAmount+$fyearvalue, 2, '.', ',')/number_format($AircraftCost, 2, '.', ','))*100;
 echo $str.='<tr class="style14" height=30 style4><td colspan=2>Total Deductions</td><td colspan=2>$'.number_format($Section179Amount+$BonusDepAmount+$fyearvalue, 2, '.', ',').' - '.number_format($percent, 0, '.', ',').'% (of cost)</td></tr>';

I am using the *100 to take the decimal value and convert to %
Example:  400000/500000 = .8
.8 *100 = 80%

This works fine for this calculation but when I change the values to 620000/1000000 the % calculates to 62,000 % ???

What am I doing wrong?