calculateDiscount

calculateDiscount is a function or method used in pricing, commerce, and software development to determine a discounted price or the amount of discount applied. It takes a base price and a discount specification and returns a numeric result representing the price after discount or the discount amount, depending on the implementation.

Common forms include percentage-based discounts and flat-amount discounts. A typical percentage form is calculateDiscount(price, discountRate), which returns price * (1 - discountRate). A flat form is calculateDiscount(price, discountAmount), which returns max(0, price - discountAmount) to prevent negative prices. Some implementations accept a structured parameter, such as calculateDiscount(price, { rate, cap }), where rate is a decimal or percentage and cap limits the maximum discount.

Return values are usually the discounted price, though some variations return the amount discounted. In practice, a function may also expose options for rounding, currency formatting, or minimum price constraints.

Examples: with price = 100 and discountRate = 0.2, the result is 80. With price = 100 and discountAmount = 15, the result is 85. If a discount would produce a negative or zero price, a common approach is to clamp the result at zero.

Important considerations include input validation, handling of edge cases (such as zero or negative prices), and how to interpret percentage inputs (0–1 vs. 0–100). Documentation should clarify the expected parameter types, behavior, and any constraints, and unit tests should cover typical, boundary, and error scenarios. Related concepts include discounts, coupons, promotions, and pricing strategies.