2.5% is the change from 800 to 820
Calculation steps:
[( 820 - 800 ) ÷ 800] x 100 = 2.5%
Formula
Percentage change = [(820 - 800) / 800] x 100
Subtract the new number by the original number
820 - 800 = 20
20 ÷ 800 = 0.025
0.025 x 100 = 2.5%
Example