How to calculate a discount
Calculating a discount means reducing an original value by a given percentage. The three most common operations are: figuring out what a price becomes after a discount, finding what discount percentage was applied between two prices, and calculating the effect of discounts applied one after another.
Discounted price formula
final price = original price × (1 − discount ÷ 100). A $200 item with a 15% discount comes to 200 × (1 − 0.15) = $170, a $30 savings.
Formula to find the applied discount
discount (%) = ((original price − final price) ÷ original price) × 100. If a $200 item now costs $170, the discount was (200 − 170) ÷ 200 × 100 = 15%.
Why two 10% discounts aren't a 20% discount
This is one of the most common mistakes when calculating sales. Stacked discounts apply to the value already reduced by the previous one, not added together directly. A $200 item with a 10% discount comes to $180. Applying another 10% on top of $180 brings the final price to $162, an effective discount of 19%, not 20%. The more discounts you stack, the bigger the gap between the simple sum and the real discount.
Practical example
A store advertises "10% + 10%" off during a sale. Many people read that as a 20% discount, but the actual savings are smaller. Using the stacked discount calculator above avoids that trap and shows the real effective discount, plus the exact final price.