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Simple interest as linear growth
Simple interest is the most basic interest model in finance. Unlike compound interest, which earns interest on previously earned interest, simple interest is calculated only on the original principal balance. This means the interest added each period is constant, causing total value to grow linearly over time rather than exponentially.
This structure is commonly used in short-term notes, educational examples, introductory credit products, and certain bond calculations. It is valuable because it isolates the effect of the rate and the time period without introducing reinvestment or capitalization effects.