To calculate percentage change in a stock's price, use this formula: ((New Price - Old Price) / Old Price) × 100.
For example, if a stock was trading at $50 and is now $60, the calculation is ((60 - 50) / 50) × 100 = (10 / 50) × 100 = 20%. This means the stock gained 20%.
For a stock that declined from $80 to $60: ((60 - 80) / 80) × 100 = (-20 / 80) × 100 = -25%, representing a 25% loss.
The key principle is always dividing the change by the original price, not the new price. This ensures the percentage is measured relative to where the investment started. This same method applies whether you're measuring change over one day, one month, one year, or any time period.
When comparing multiple stocks, percentage change is more useful than absolute dollar change because it accounts for different starting prices. A $10 gain on a $100 stock (10%) is proportionally different from a $10 gain on a $200 stock (5%), even though the dollar amount is identical.
You can also calculate percentage change between any two points in a stock's history—from open to close on a given day, week-to-week, or year-to-year—using the same formula. Financial websites typically display percentage change automatically, but understanding the calculation helps you verify figures and compare investments meaningfully.