Loop calculation not working as expected

Can someone help, don’t know how to solve this using loop in php. 

$pay = [20, 40 , 89, 300, 190, 15]; 
$Capital = 1000; 
I want the loop to achieve this result 
1000-20 = 980 
980-40 = 940 
940-89 = 851 
851-300 = 551 
551-190 = 361 
361-15 = 346 

My code is:
$newbal = $Capital-$pay
for ($amount=$newbal; $amount>=$Capital; $amount-=$pay) { 
echo "{$amount}"; 
$amount++; 
} 
My code is giving me this result:
1000-20 = 980 
1000-40 = 960 
1000-89 = 911 
1000-300 = 700 
1000-190 = 810 
1000-15 = 985