Wealth Growth Tool
Model how your investments grow with regular contributions. Discover how time, return rate, and compounding frequency interact to build exponential wealth.
Written by Mike Starr
Founder, StackedTomorrow · M.S. Organizational Management
Last Reviewed: August 2026
Educational Content Only. All content on this page is provided for informational and educational purposes only. It does not constitute financial, investment, legal, tax, or retirement advice. The calculators and projections shown are illustrative models — not predictions or guarantees of future performance. Past performance does not guarantee future results. Always consult a qualified financial professional before making investment or retirement decisions.
Discover the exact year you reach any wealth milestone — from $1M to $1B.
Simulation Mode
Retire anywhere in the world with total, unlimited freedom.
The green line shows your target. Once you cross it, compounding continues — wealth doesn't stop at your goal, it accelerates beyond it.
Compound interest is the mathematical process by which investment returns generate their own returns. The core formula is: A = P(1 + r/n)^(nt), where A is the final amount, P is the principal, r is the annual interest rate, n is compounding frequency, and t is time in years.
What makes compound growth remarkable isn't the formula — it's the behavior it produces. In the early years, growth appears linear and modest. But in later years, the same percentage return applies to an exponentially larger base, producing accelerating dollar gains. A $100,000 portfolio growing at 7% earns $7,000 in year one. By year 30, that same 7% earns over $50,000 in a single year — from a base that compounding itself built.
This acceleration is why financial advisors universally emphasize starting early. See our complete compound interest guide for the "Alex vs. Jordan" case study that quantifies exactly how much starting 10 years earlier is worth in final portfolio value.
The Rule of 72 is a simple mental calculation: divide 72 by your annual return rate to estimate how many years it takes to double your money. It's accurate within 1–2% of the mathematically precise answer across typical investment return ranges.
| Return Rate | Rule of 72 Estimate | Actual Doubling Time |
|---|---|---|
| 4% | 18 years | 17.7 years |
| 6% | 12 years | 11.9 years |
| 7% | 10.3 years | 10.2 years |
| 8% | 9 years | 9 years |
| 10% | 7.2 years | 7.3 years |
| 12% | 6 years | 6.1 years |
Source: Rule of 72 is a mathematical approximation. Actual doubling time = ln(2)/ln(1+r). Shown values assume annual compounding with no additional contributions.
A common misconception is that finding a higher-return investment is the key to wealth building. In reality, time horizon matters more than return rate for most investors. Consider these two scenarios, both starting with $0 and investing $500/month:
Alex
Starts at 22 at 7% return
~$2,590,000 by age 62
Jordan
Starts at 32 at 9% return
~$1,550,000 by age 62
Alex earns 2% less per year but starts 10 years earlier — and still ends up with 67% more money. Those extra 10 years of compounding are worth more than the 2% return advantage. This is the mathematical argument for starting as early as possible, even with small amounts.
Different investment vehicles harness compound growth differently:
Index Funds & ETFs: Returns compound through price appreciation and reinvested dividends. Long-run returns ~7–10% nominal. The primary vehicle for most FIRE strategies. → Index Fund
401(k) and IRA: Tax-advantaged accounts where compound growth occurs without annual tax drag. Tax-deferred compounding significantly accelerates wealth accumulation versus taxable accounts. → IRA
High-Yield Savings (HYSA): Compound interest on cash — currently 4–5% APY. Best for emergency funds and short-term goals. Not appropriate for long-term wealth building due to inflation risk. → APY
Dividend Reinvestment: Dividend payments automatically reinvested purchase additional shares, which then generate their own dividends. A pure compound growth mechanism within dividend investing. → Dividend Investing Guide
Tax drag is the reduction in compound growth caused by paying taxes on investment returns each year. In a taxable brokerage account, annual dividend payments and capital gains distributions are taxable events — reducing the capital available to compound next year.
The solution is maximizing tax-advantaged accounts — 401(k), IRA, and HSA contributions — before investing in taxable accounts. A $10,000 gain in a Roth IRA compounds with zero annual tax drag; the same gain in a taxable account is reduced by 15–20% capital gains tax on dividends and realized gains. Over 30 years, this difference is substantial — commonly 15–25% higher final portfolio value inside tax-advantaged accounts.