-20.98% is the change from 815 to 644
Calculation steps:
[( 644 - 815 ) ÷ 815] x 100 = -20.98%
Formula
Percentage change = [(644 - 815) / 815] x 100
Subtract the new number by the original number
644 - 815 = -171
-171 ÷ 815 = -0.2098159509202454
-0.2098159509202454 x 100 = -20.98%