Project your investment portfolio growth combining an initial deposit with regular monthly contributions. Model different return rates and time horizons to plan your financial goals with confidence.
This calculator combines two compound interest formulas. The initial lump sum grows using FV = PV × (1 + r)^n. Monthly contributions use the future value of an annuity: FV = PMT × [(1 + r)^n − 1] / r. Both use a monthly compounding rate derived from your annual return rate. The results are added together to show total portfolio value.
The annual return rate you enter represents your assumed average annual growth. For broad stock market index funds, the historical average annual return of the S&P 500 is approximately 10% before inflation, or about 7% after adjusting for inflation. Conservative portfolios with bonds typically average 4–5%. A 7% real return assumption is commonly used for long-term retirement projections.
$200/month at 7% return: Starting at 25 and investing until 65 (40 years) → final value = $524,254. Starting at 35 and investing until 65 (30 years) → final value = $243,994. Starting 10 years earlier more than doubles the outcome despite only contributing $24,000 more.
Option A: $20,000 lump sum at 7% for 20 years = $77,394. Option B: $83/month for 20 years at 7% = $51,748 (same total contribution of ~$20,000). The lump sum wins because the entire amount compounds from day one, while monthly contributions average only 10 years in the market.
$5,000 initial + $300/month for 25 years: At 5% = $176,424. At 7% = $243,025. At 9% = $337,118. The 2% rate difference between 7% and 9% produces nearly $100,000 more — illustrating why low-fee index funds outperform high-fee actively managed funds over long periods.
For long-term stock market investments in diversified index funds, 6–8% annually is a reasonable real return assumption (after inflation). For conservative bond-heavy portfolios, 3–4% is more realistic. For cash savings accounts, use your current APY. Never guarantee or count on any specific return — markets fluctuate, and past performance does not guarantee future results. Use multiple scenarios (5%, 7%, 9%) to model a range of outcomes rather than relying on a single projection.
A common rule of thumb is the 4% rule: at retirement, you can safely withdraw 4% of your portfolio annually with low risk of running out of money over 30 years. So if you need $50,000/year in retirement income, you'd need approximately $1,250,000 saved. Use this calculator to project whether your current savings rate puts you on track.
Mathematically, investing a lump sum immediately tends to outperform spreading it over time (dollar-cost averaging) because more money compounds for longer. However, dollar-cost averaging reduces risk by buying at various price points. For regular income, monthly contributions are the practical choice. If you receive a windfall, investing it immediately rather than gradually is historically more likely to produce better returns.
A nominal return is the raw percentage gain. A real return adjusts for inflation. If your investment earns 8% but inflation is 3%, your real return is approximately 5%. For retirement planning, always consider real returns to understand your actual purchasing power growth.
Investment fees compound just like returns — but against you. A 1% annual expense ratio on a $100,000 portfolio over 30 years at 7% costs approximately $180,000 in foregone returns compared to a 0.1% fee fund. Low-cost index funds typically charge 0.03–0.20% annually, while some actively managed funds charge 1–2%. This difference is one of the most impactful factors in long-term investing.
Dollar-cost averaging means investing a fixed amount on a regular schedule regardless of market conditions. When prices are low, your fixed dollar amount buys more shares. When prices are high, it buys fewer. Over time, this averages your purchase price and reduces the risk of investing a large sum right before a market decline. It's the natural result of contributing monthly to a 401(k) or IRA.