Written by
WealthCalcLab Research Desk
Calculator methodology and consumer finance research
Reviewed by
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Published
April 5, 2026
Original article date
Last updated
April 5, 2026
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Sources and references
The core difference
Simple interest is calculated only on the original principal. Compound interest is calculated on the principal plus previously earned interest.
In short time periods the difference can appear small. Over long periods the difference can become substantial because compounding creates growth on growth.
Where each one appears
Simple interest is common in introductory borrowing examples and some short-term products. Compound interest is more common in savings and investment contexts because returns are often reinvested.
Understanding which method applies helps you judge whether a quoted rate is more or less meaningful than it first appears.
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