Investment Calculator

An investment calculator is a tool that estimates how much a sum of money will grow over time based on your initial investment, regular contributions, expected return rate, and time horizon. It uses the compound interest formula to model growth, showing you both your total balance and the breakdown between money you contributed and returns earned on that money.

At a 7% annual return, a $500 monthly investment starting from zero reaches $1 million in approximately 37 years. If you already have $10,000 invested, you reach $1 million in about 34 years with the same monthly contribution. Starting earlier or contributing more shortens the timeline significantly. You can test any combination in the calculator above.

For a diversified portfolio of low-cost index funds, most financial planners use 6-8% as a real-world planning assumption after inflation. The S&P 500 has averaged 10.2% annually since 1957 before inflation, according to data from NYU Stern School of Business. For a conservative retirement plan, 6% is a reasonable assumption. For modeling optimistic scenarios, 9-10% is commonly used.

Compound interest means you earn returns on your returns, not just on your original investment. If you invest $10,000 at 7% annual return, you earn $700 in year one. In year two, you earn 7% on $10,700, which is $749. Each year, the base grows, and so does the return. Over 30 years at 7%, your $10,000 becomes approximately $76,000 without adding a single additional dollar. That growth comes entirely from compounding.

Research consistently shows that investing a lump sum as early as possible outperforms spreading the same amount over time, because the full principal benefits from compounding sooner. However, monthly contributions from income is the practical approach for most investors. The best strategy is the one you can consistently follow.

Yes. This calculator is completely free to use and requires no account or signup. All calculations run directly in your browser, which means your numbers are never sent to our servers or stored anywhere.

Investment calculators model a simplified version of reality. They assume a constant annual return, which actual markets do not provide. Real portfolios experience year-to-year volatility. Calculators are useful for goal-setting and understanding the impact of time, contributions, and return rates, not for predicting exact future values.

A standard investment calculator answers: how much will my money grow? A FIRE calculator (Financial Independence, Retire Early) answers: how much do I need to reach financial independence, and when will I get there? The FIRE calculator incorporates your annual expenses, target withdrawal rate, and savings rate to estimate your independence date. Use this calculator to model a specific investment. Use the FIRE calculator to plan your full retirement picture.