Investment Calculator
See how your money grows over time with compound interest and regular contributions. Enter your starting amount, monthly contributions, expected return rate, and time horizon to project your investment's future value.
Compound interest is the single most powerful force in long-term investing. When your returns generate their own returns, growth accelerates dramatically over time. A $10,000 initial investment with $500 monthly contributions at 8% annual return grows to about $335,000 after 20 years. Of that total, you only contributed $130,000 out of pocket. The remaining $205,000 came from compound growth.
The formula behind this calculator is FV = P(1+r)^n + PMT x [((1+r)^n - 1) / r], where P is your initial investment, r is the monthly interest rate, n is the total number of months, and PMT is your monthly contribution. This assumes returns compound monthly and contributions happen at the end of each month.
Time in the market matters more than timing the market. Starting five years earlier with the same contributions can mean hundreds of thousands of dollars more at retirement. For example, investing $500 per month starting at age 25 versus age 30 (both at 8% return until age 65) results in roughly $1.75 million versus $1.15 million. That five-year head start adds over $600,000 in extra growth.
Keep in mind that actual market returns vary year to year. The S&P 500 has historically returned about 10% annually before inflation (roughly 7% after inflation). This calculator uses a fixed rate for projection purposes. Real-world results will fluctuate, but over long periods, the math of compounding holds remarkably well.