You put in $200 at 10% interest compounded yearly for 2 years. No fees. Total?

How $200 Grows to $242 With Compound Interest

Two years, 10% interest, and a starting pot of $200 — the math lands you at exactly $242. It sounds simple, but understanding why that number is what it is reveals one of the most powerful forces in personal finance.

The Magic of Compounding in Action

Here's what actually happens to your money. At the end of year one, you earn 10% on your original $200. That's $20, bringing your total to $220. Straightforward enough.

Year two is where compounding shows its hand. You don't earn 10% on the original $200 again — you earn 10% on the new balance of $220. That gives you $22 in interest, not $20. Add that to $220 and you land at $242.

The formula behind this is A = P × (1 + r)ⁿ, where P is your principal ($200), r is the annual interest rate (0.10), and n is the number of years (2). Plug those in: 200 × 1.1 × 1.1 = 200 × 1.21 = $242. Clean, exact, no rounding needed.

Simple Interest Would Have Given You Less

This is worth pausing on. If the account had paid simple interest instead — meaning interest only ever calculated on the original $200 — you'd earn $20 each year and finish with $240 after two years. That's $2 less than compound interest delivers.

Two dollars might not seem like much, but the gap widens dramatically over longer time horizons and larger amounts. That's why Albert Einstein is often (if apocryphally) credited with calling compound interest "the eighth wonder of the world." Whether he said it or not, the math backs it up.

Why 10% Is a Meaningful Benchmark

Ten percent isn't a random figure. It's historically close to the average annual return of the U.S. stock market, particularly the S&P 500 index, when measured over long periods. Since its inception in 1957, the S&P 500 has delivered average annual returns of roughly 10–11% before inflation adjustments. Financial educators often use 10% as a teaching rate precisely because it's realistic, not just convenient.

The Lesson That Scales Up

The real power of this example is what it implies at scale. Imagine that same 10% annual compounding on $20,000 over 20 years — you'd end up with over $134,000, more than six times your money, without adding a single extra dollar. The gains in the later years vastly outpace the early ones, because each year's interest base is larger than the last.

This is why financial advisors hammer home the importance of starting early. Time is the multiplier. Even modest amounts, given enough runway and a consistent rate, snowball into something significant. Your $200 example is the miniature version of a principle that underlies retirement accounts, index fund investing, and long-term wealth building worldwide.