-86.23% is the change from 661 to 91
Calculation steps:
[( 91 - 661 ) ÷ 661] x 100 = -86.23%
Formula
Percentage change = [(91 - 661) / 661] x 100
Subtract the new number by the original number
91 - 661 = -570
-570 ÷ 661 = -0.8623298033282905
-0.8623298033282905 x 100 = -86.23%