How Compound Interest Actually Works

You know it is important. You have heard it described as the eighth wonder of the world by people who enjoy sounding clever. This explains it with actual numbers, shows you the Rule of 72, and uses the credit card example that makes the warning actually land.

Explain compound interest to someone who has basic numeracy but no financial background. Use a concrete example: {STARTING_AMOUNT} invested at [an interest rate you choose] over [a time period you choose]. Show:
1. The calculation step by step for the first three years
2. What compounding frequency means (annual, monthly, daily) and how it changes the outcome with a comparison
3. The Rule of 72 and how to use it as a quick mental estimate
4. One common mistake people make when ignoring compound interest, using a credit card or loan as the example

Keep the explanation in plain English with no jargon. Close with the core insight in one sentence.