Investing Calculators

Compound interest is the most powerful force in personal finance, but it is also the most abstract. Telling someone their money will "grow exponentially" does not change behavior. Showing them that $500 a month at 7 percent turns into $566,000 in 30 years — and that $260,000 of that is pure growth on growth — does. That is what our investing calculators are for. They turn the abstract math of compounding into specific dollar amounts based on your actual numbers.

These tools are for anyone who invests or is thinking about starting. If you are opening your first brokerage account and want to see what $200 a month could become over 20 years, the Compound Interest Calculator models it. If you are an experienced investor comparing the projected outcome of different contribution levels or return assumptions, the Investment Return Calculator runs multiple scenarios. If you want to estimate passive income from a dividend portfolio — and see how reinvesting those dividends accelerates growth — the Dividend Calculator breaks it down. And if you are saving toward a specific goal like a house down payment or an education fund, the Savings Calculator shows how much to set aside each month and when you will hit your target.

A few things to understand about how these projections work. The calculators show future values based on the inputs you provide: starting amount, monthly contribution, expected rate of return, and time horizon. Returns are nominal by default, meaning they do not subtract inflation. A 7 percent average annual return is a widely used benchmark for a diversified stock portfolio based on historical S&P 500 data, but actual year-to-year returns range from roughly negative 40 percent to positive 50 percent. The smooth growth curve in the chart represents an average trajectory, not a prediction of any single year. These are planning tools, not crystal balls. Running scenarios at both 5 percent (conservative) and 9 percent (optimistic) gives you a realistic range.

The most common mistake people make with investment projections is using unrealistic return assumptions. Plugging in 12 or 15 percent will produce exciting-looking charts, but no broadly diversified portfolio sustains those returns over decades. The second mistake is ignoring inflation. A million dollars 30 years from now buys significantly less than a million dollars today. If you want to plan in today’s purchasing power, subtract estimated inflation (roughly 2 to 3 percent) from your return assumption — so use 4 to 5 percent real instead of 7 percent nominal. Third, do not overlook fees. A seemingly small 1 percent annual management fee can reduce your ending portfolio balance by 20 to 30 percent over a 30-year period compared to a 0.1 percent index fund. The math is unforgiving because fees compound against you the same way returns compound for you.

Perhaps the most important insight these calculators reveal is the power of time. Starting 10 years earlier often matters more than doubling your monthly contribution. Someone who invests $300 a month from age 25 to 65 at 7 percent accumulates far more than someone who invests $600 a month from age 35 to 65. The first decade of compounding creates the foundation that all future growth builds on. Run the comparison yourself — the numbers are striking.