Investment Growth Calculator
Pre-set to 10% — the approximate historical nominal return of the S&P 500. Adjust the rate to model different asset classes or risk levels.
Historical Returns by Investment Type
| Investment | Avg. Annual Return (Historical) | Risk Level | Notes |
|---|---|---|---|
| S&P 500 Index Fund | ~10% nominal, ~7% real | Medium-High | 1926–2025 average |
| Total US Stock Market | ~10% | Medium-High | Similar to S&P 500 |
| International Stocks (VXUS) | ~7–8% | Medium-High | Lower recent performance |
| Mutual Funds (active) | ~6–8% (net of fees) | Medium-High | Often underperform index funds |
| Real Estate (REITs) | ~9–10% | Medium | Including dividends |
| US Bonds (AGG) | ~4–5% | Low | Lower volatility |
| 60/40 Portfolio | ~7–8% | Medium | Classic balanced allocation |
Dollar-Cost Averaging: Why Monthly Contributions Beat Lump-Sum Timing
Dollar-cost averaging (DCA) means investing a fixed amount on a regular schedule regardless of market conditions. The monthly contribution field in this calculator models exactly this strategy.
DCA in action
Investing $300/month over 25 years at 10% produces ~$398,000. Trying to "time the market" and missing just the 10 best days in those 25 years reduces that to ~$230,000. Consistency beats timing every time.
Index Funds vs Actively Managed Mutual Funds
The compound interest calculator reveals a critical insight: fees compound just like returns do — but in reverse.
| S&P 500 Index Fund | Active Mutual Fund | |
|---|---|---|
| Typical expense ratio | 0.03–0.10% | 0.5–1.5% |
| $100k after 30 yrs @ 10% gross | $1,719,243 | $1,325,677 (1% fee) |
| Fee cost over 30 years | ~$5,000 | ~$393,566 |
| % of returns lost to fees | <1% | ~23% |
The Rule of 72 for Investments
Divide 72 by your expected annual return to estimate how quickly your portfolio doubles:
- At 6%: doubles every 12 years — $10k → $20k → $40k → $80k in 36 years
- At 8%: doubles every 9 years — $10k → $80k in 27 years
- At 10%: doubles every 7.2 years — $10k → $80k in just 21.6 years
Frequently Asked Questions
The S&P 500 has returned approximately 10% annually before inflation over the long run. After inflation (typically ~3%), the real return is ~7%. For conservative planning, use 6–7%. For a reality check, run numbers at both 5% and 10% to understand the range. Past returns don't guarantee future performance.
Mutual funds compound through reinvested dividends and capital gains distributions. When dividends are reinvested, they buy more shares, which generate more dividends — the classic compounding loop. Growth funds that don't pay dividends compound through share price appreciation alone. Always enable dividend reinvestment (DRIP) for maximum compounding.
Research shows lump-sum investing beats dollar-cost averaging about 2/3 of the time, because markets go up more often than down. However, DCA wins emotionally — it removes the anxiety of timing the market and keeps you invested through volatility. If you have a lump sum, investing it immediately (or over 3–6 months) is statistically optimal, but DCA monthly contributions is excellent practice.