Answer:
Percentage change between two numbers A & B can be calculated as:
(B-A)/A * 100
For example, if a stock price increases in value from $123 to $145 the percentage increase is:
(145-123)/123 * 100 = 17.9%
Alternatively, if a stock price decreases in value from $145 to $123 the percentage decrease is:
(123-145)/145 * 100 = 15.2%