Investment Return Calculator
Project the future value of an investment with a lump-sum start and regular monthly contributions at a given annual return. Use it to plan retirement savings, college funds, or any long-term investment goal.
About this calculator
This calculator uses the future value formula for a lump sum combined with the future value of an annuity. The total future value is: FV = I × (1 + R)^T + C × 12 × ((1 + R)^T − 1) / R, where I is the initial investment, C is the monthly contribution, R is the expected annual return expressed as a decimal (expectedReturn / 100), and T is the investment period in years. The first term compounds your starting balance; the second term accumulates all annual contributions (monthly × 12) as a simple annual annuity. An optional inflation rate lets you see the real purchasing power of that future sum by discounting: Real FV = FV / (1 + inflationRate/100)^T.
How to use
Say you invest $10,000 today, add $500/month, expect 7% annual return, and plan to invest for 20 years. R = 0.07, T = 20, annual contributions = $500 × 12 = $6,000. FV = 10,000 × (1.07)^20 + 6,000 × ((1.07)^20 − 1) / 0.07. That gives 10,000 × 3.8697 + 6,000 × 40.9955 = $38,697 + $245,973 = $284,670. If inflation is 3%, the real value is roughly $284,670 / (1.03)^20 ≈ $157,500 in today's dollars.
Frequently asked questions
How does compound interest affect long-term investment returns?
Compound interest means you earn returns not just on your original principal but also on all previously accumulated gains. Over long periods this creates exponential rather than linear growth — commonly called the snowball effect. A $10,000 investment at 7% doubles roughly every 10 years, reaching about $38,700 after 20 years without a single additional contribution. The longer the horizon, the more dramatic the compounding effect becomes, which is why starting early is the single most powerful investment decision.
What is a realistic expected annual return to use in an investment calculator?
Historically, a diversified portfolio of large-cap US stocks (S&P 500) has returned roughly 10% annually before inflation, or about 7% after inflation, over long periods. Bond-heavy portfolios typically return 3–5% nominal. A balanced 60/40 portfolio has averaged around 7–8% nominal. Always use conservative assumptions — planners often recommend 6–7% nominal for retirement projections to account for fees, taxes, and market variability. Running the calculator with both optimistic and pessimistic rates shows you a realistic range.
Why does inflation matter when calculating investment returns?
Inflation erodes the purchasing power of future money, so a nominal gain of $284,000 in 20 years is not the same as having $284,000 in today's dollars. At 3% annual inflation, prices roughly double every 24 years, meaning your future balance buys far fewer goods and services. Dividing the nominal future value by (1 + inflationRate)^T converts it to real (inflation-adjusted) dollars, giving a true picture of your wealth. Always compare your expected investment return to expected inflation to know your real return.