Simple interest vs Compound interest
Simple interest
Applies the rate to original principal only.
Compound interest
Applies the rate to principal plus accumulated interest.
Use one example to see the difference
Start with the same underlying transaction or business period, calculate both measures, and label what each includes. The numbers may be mathematically correct while still answering different management or investment questions.
When should you use simple interest vs compound interest?
Use the method stated by the contract or product; do not choose based on which result looks preferable.
Limitations and common mistakes
The comparison becomes misleading when the two measures use different periods or definitions.
Do not mix annual figures with monthly figures, ending balances with averages, or percentages with whole numbers. Record the definition used so another person can reproduce the result.
Frequently asked questions
What is simple interest vs compound interest?
Simple interest and Compound interest answer different questions and should not be substituted without checking the decision.
How should I use simple interest vs compound interest?
Use the formula only after matching every input to the same period, unit and definition. Then compare the result with a worked example and the decision you are trying to make.
What is the most common mistake with simple interest vs compound interest?
The comparison becomes misleading when the two measures use different periods or definitions.
Can I calculate simple interest vs compound interest in a spreadsheet?
Yes. Reproduce the displayed equation with separate cells for each input, keep percentages as decimals, and test the spreadsheet against the worked example before replacing the sample figures.
Sources and methodology
This page uses the Investor.gov Compound Interest Calculator for the underlying financial or reporting context. Spreadsheet-related behavior is checked against Microsoft’s financial-function documentation. Examples are illustrative and use the formula displayed on the page.