Understanding the interest calculator
Interest is the price of money over time earned when you lend or save, paid when you borrow. This calculator compounds a starting balance and any monthly additions at a fixed annual rate, showing how contributions and compounding combine. The interest portion grows every period because it's calculated on an ever-larger balance.
Two levers dominate the outcome: the rate and the time. Doubling the rate roughly doubles the interest in the short run, but adding years matters more over long horizons because compounding is exponential. Small, consistent monthly contributions often out-earn a larger one-time deposit made years later, simply because they spend more time compounding.
Results are estimates for education only and are not financial advice.