The compound interest time bomb

Compound interest is the dullest-sounding topic in finance and the most consequential. It's the difference between your future and your parents' future. It's why starting at 22 is worth more than starting at 32 even if you contribute three times as much in the second case. Most people are taught about it abstractly. We're going to operate it.

Two paths. Same person. Same income. Different choices. Drag the sliders to set the assumptions and watch how a few decisions in your 20s compound into entire different lives.

The 7% rule and rule of 72

Two shortcuts worth memorizing: the long-run real return on the US stock market (after inflation) is roughly 7% per year. And the "Rule of 72" says to find how long money takes to double, divide 72 by your interest rate. At 7%, money doubles every ~10 years. At 22% (a typical credit card APR), debt doubles every ~3.3 years. This is why credit card debt is so devastating — the doubling time is short enough that interest passes principal in just a few years.

Why this matters politically

Two people with identical incomes can end up at radically different net worths just because one had access to investment vehicles (a 401(k) match, low-fee index funds, financial education) and one didn't. The ones who don't are usually the ones who can't afford a financial advisor, which means we systematically funnel this knowledge to those who already have wealth, and the gap compounds at — yes — about 7% a year.