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Compare Investments Using the Rule of 72

Quick definition: Comparing investments with Rule of 72 means calculating doubling time for each option, accounting for fees and taxes, then projecting final wealth to choose the best fit for your goals and time horizon.

Key takeaways​

  • Different asset classes have dramatically different doubling times: savings (35 years) vs. stocks (7 years) vs. venture capital (3–5 years)
  • Fee and tax drag compound into massive wealth gaps; a 1% fee costs you 15–20% of final wealth
  • Comparing investments requires adjusting for risk—higher returns may be possible but not probable
  • Time horizon changes which investment wins: bonds outperform stocks for <5-year goals; stocks dominate for 20+ year timelines
  • Real-world comparison must subtract inflation and taxes, not just compare headline rates

Comparing bonds vs. stocks: The classic tradeoff​

Scenario: You have $100,000 to invest for 30 years. Refer to the doubling-time table for exact calculations on any return rate.

Bond-fund option​

  • Historical return: 5% annually
  • Doubling time: 72 ÷ 5 = 14.4 years
  • Doublings in 30 years: 30 ÷ 14.4 = 2.08 doublings
  • Nominal final value: $100,000 × 2.08² = ~$433,000
  • After 25% tax: Effective return ≈ 3.75%, doubling ≈ 19.2 years, doublings ≈ 1.56 = 2.95×, final: ~$295,000
  • After 2.5% inflation erosion (50% over 30 years): Real value ≈ $147,500

Stock-fund option​

  • Historical return: 10% annually
  • Doubling time: 72 ÷ 10 = 7.2 years
  • Doublings in 30 years: 30 ÷ 7.2 = 4.17 doublings
  • Nominal final value: $100,000 × 2^4.17 ≈ $18 × $100,000 = ~$1,800,000
  • After 25% tax (long-term capital gains at lower rates, assume 15%): Effective return ≈ 8.5%, doubling ≈ 8.5 years, doublings ≈ 3.5 = 11×, final: ~$1,100,000
  • After 2.5% inflation: Real value ≈ $550,000

Difference: Stocks deliver $550,000 in real purchasing power vs. bonds' $147,500—a 3.7× advantage over three decades. This explains why financial advisors emphasize equities for long time horizons.

But this ignores volatility: stocks can drop 40–50% in downturns, creating psychological pressure to sell. Bonds are stable. The choice depends on whether you can endure volatility for higher expected returns.

Comparing low-cost vs. high-cost funds: The fee impact​

Scenario: $200,000 invested for 25 years in diversified U.S. stock funds.

Low-cost index fund​

  • Expense ratio: 0.05% annually
  • Pre-fee return (from market): 10%
  • Actual return to you: 9.95%
  • Doubling time: 72 ÷ 9.95 ≈ 7.24 years
  • Doublings in 25 years: 25 ÷ 7.24 ≈ 3.45 doublings = 11×
  • Nominal final value: $200,000 × 11 = $2,200,000

Actively managed fund​

  • Expense ratio: 1.0% annually
  • Pre-fee return (from market): 10%
  • Actual return to you: 9.0%
  • Doubling time: 72 ÷ 9 = 8 years
  • Doublings in 25 years: 25 ÷ 8 = 3.125 doublings ≈ 8.6×
  • Nominal final value: $200,000 × 8.6 = $1,720,000

Difference: The 0.95% fee gap costs $480,000 in final wealth—a 22% reduction. Over 25 years, that seemingly small 1% annual fee compounds into enormous opportunity cost.

If the active fund outperforms by 1% (beating the index), it breaks even. If it underperforms (the historical norm), you lose money net of fees. This is why low-cost index funds dominate for most investors—the fee math is overwhelming.

Adding taxes to the fee comparison​

If the low-cost index fund is in a taxable account:

  • Index funds make small, infrequent distributions
  • Tax on $2,200,000 (assuming 15% long-term capital gains rate): ~$330,000
  • After-tax proceeds: ~$1,870,000
  • After inflation (2.5% × 25 years ≈ 55% erosion): ~$841,000

If the active fund is also taxable:

  • Actively traded funds trigger more taxable events
  • Tax on $1,720,000: ~$258,000
  • After-tax proceeds: ~$1,462,000
  • After inflation: ~$657,000

Even after tax, the index fund's $841,000 beats the active fund's $657,000 by $184,000. In a tax-deferred account (401(k), IRA), this gap vanishes because neither is taxed until withdrawal—a huge reason to maximize tax-deferred investing.

Comparing real estate vs. stocks​

Scenario: $300,000 down payment on a rental property vs. $300,000 in an S&P 500 index fund, 25-year horizon.

Stock investment​

  • Expected return: 10% annually
  • Doubling time: 7.2 years
  • Doublings in 25 years: 3.5 = ~11×
  • Final value: $300,000 × 11 = $3,300,000
  • Less long-term capital gains tax (15%): $3,300,000 × 0.85 = $2,805,000
  • Less inflation (55% erosion): ~$1,262,000 in real value

Real estate investment (rental property)​

  • Purchase price: $300,000 (down payment on $1.5M property financed at 80%)
  • Mortgage: $1.2M at 4%, 30-year term
  • Rent collected: $1,500/month initially, rises 3% annually (tracking inflation)
  • Property appreciation: 3% annually (historical real-estate average)
  • Annual expenses: property tax (1.2% of value), insurance (0.5%), maintenance (1%), vacancy (5%) = 7.7% of rent collected
  • Net cash flow: Positive but modest; most returns come from appreciation

Calculation (simplified):

  • Property appreciation: $1.5M × 3% annually, doubling time: 72 ÷ 3 = 24 years (one doubling)
  • After 25 years: ~$1.5M × 2.5 ≈ $3.75M property value
  • Remaining mortgage: ~$400K (30-year term)
  • Home equity: $3.75M − $400K = $3.35M
  • Less capital gains tax (25% of gains on $2.35M gain = $587K): ~$2.76M
  • Less inflation erosion: ~$1.24M real value
  • Add net cash-flow accumulation (modest, maybe $50K total): ~$1.29M real value

Comparison:

  • Stocks: $1.26M real value (hands-off, liquid, diversified)
  • Real estate: $1.29M real value (illiquid, time-intensive property management, concentrated)

The real-estate advantage is tiny (2% higher), but it comes with:

  • Leverage (the bank financed 80%)
  • Inflation hedge (rents and property values rise with inflation)
  • Tax deductions (mortgage interest, property tax, maintenance are deductible)
  • Forced savings (mortgage payments force you to save)

Stocks win on simplicity and liquidity. Real estate wins on leverage and tax efficiency. The tradeoff depends on your skill, time, and personality.

Comparing bonds with different maturity dates​

Scenario: $50,000 to invest for 20 years in U.S. Treasuries.

20-year Treasury bonds​

  • Current yield: 4.5% (as of 2024–2026 rates)
  • Doubling time: 72 ÷ 4.5 ≈ 16 years
  • Doublings in 20 years: 20 ÷ 16 = 1.25 doublings ≈ 2.4×
  • Final value: $50,000 × 2.4 = $120,000
  • After 25% tax: Effective return 3.375%, doubling 21.3 years, doublings 0.94 ≈ 1.9×, final: ~$95,000
  • After inflation: ~$48,000 real value (no growth in purchasing power!)

Mix of short-term and long-term bonds​

  • Ladder: 25% in 5-year bonds (3%), 25% in 10-year bonds (4%), 25% in 15-year bonds (4.5%), 25% in 20-year bonds (5%)
  • Weighted average return: (3% + 4% + 4.5% + 5%) / 4 = 4.125%
  • Doubling time: 72 ÷ 4.125 ≈ 17.5 years
  • Doublings in 20 years: 1.14 ≈ 2.2×
  • Final value: ~$110,000

In a low-rate environment, even laddered bonds offer little real growth after inflation and taxes. This is why conservative investors suffered during 2010–2020 (near-zero rates): bonds didn't beat inflation.

Comparing dividend stocks vs. growth stocks​

Scenario: $150,000 to invest for 30 years.

Dividend-growth stock portfolio​

  • Dividend yield: 2.5% initially, growing 7% annually
  • Capital appreciation: 5% annually
  • Total return: ~7.5% annually (dividends + appreciation)
  • Doubling time: 72 ÷ 7.5 ≈ 9.6 years
  • Doublings in 30 years: 3.125 ≈ 8.7×
  • Final value: $150,000 × 8.7 = $1,305,000
  • Advantage: Steady income stream, reinvested for additional compounding
  • Tax drag: Dividend taxes each year slow compounding; long-term capital gains at sale

Growth-stock portfolio (no dividend)​

  • Capital appreciation: 12% annually
  • Doubling time: 72 ÷ 12 = 6 years
  • Doublings in 30 years: 5 ≈ 32×
  • Final value: $150,000 × 32 = $4,800,000
  • Advantage: No interim tax drag; all returns come at sale
  • Risk: High volatility; possibility of zero appreciation if growth slows

Comparison (nominal): Growth wins by 3.7×. But accounting for:

  • Volatility: Growth stocks can drop 50%; dividend stocks drop 25–30%. If you panic-sell at the bottom, growth loses.
  • Tax efficiency: Dividend taxes each year vs. one lump tax at sale. In a taxable account, growth has a slight edge.
  • Realism: 12% annual returns are aggressive; it assumes exceptional stock-picking or luck. Historical U.S. equity returns average 10%. A 12% assumption requires above-market performance.

For most investors, a blended portfolio (80% growth, 20% dividend) balances growth potential with income stability.

Comparing international vs. domestic investments​

Scenario: $250,000 for 20 years, comparing U.S. stocks vs. international stocks.

U.S. stock index​

  • Historical return: 10% annually
  • Doubling time: 7.2 years
  • Doublings in 20 years: 2.78 ≈ 6.8×
  • Final value: $250,000 × 6.8 = $1,700,000

International developed-market index​

  • Historical return: 8% annually (lower due to lower growth rates in mature economies)
  • Doubling time: 9 years
  • Doublings in 20 years: 2.22 ≈ 4.6×
  • Final value: $250,000 × 4.6 = $1,150,000

Emerging-market index​

  • Historical return: 11% annually (higher growth, higher volatility)
  • Doubling time: 6.5 years
  • Doublings in 20 years: 3.08 ≈ 8.3×
  • Final value: $250,000 × 8.3 = $2,075,000

On paper, emerging markets win. But volatility is severe—20–30% annual swings vs. 12–15% for U.S. stocks. A 30% drawdown in emerging markets might trigger panic-selling; you lock in losses.

A diversified approach (60% U.S., 30% developed international, 10% emerging) hedges geography while capturing upside. The slight drag from lower-returning developed markets is offset by reduced volatility and lower correlation with U.S. downturns.

Comparing investment vehicles: ETF vs. mutual fund vs. individual stocks​

Scenario: Building a $100,000 diversified stock portfolio over 25 years.

Low-cost ETF approach​

  • Expense ratio: 0.05%
  • Expected return: 10% (market return)
  • Actual return: 9.95%
  • Doubling time: 7.24 years
  • Final value: $100,000 × 11× = $1,100,000
  • Time commitment: 5 minutes to set up, 10 minutes annually to rebalance

Managed mutual fund​

  • Expense ratio: 1.0%
  • Expected return: 9% (after fees, typically underperforming)
  • Doubling time: 8 years
  • Final value: $100,000 × 8.6× = $860,000
  • Time commitment: Minimal

Individual stock picking (assumed 1% advantage over market)​

  • Expected return: 11% (if skilled)
  • Doubling time: 6.5 years
  • Final value: $100,000 × 12.3× = $1,230,000
  • Time commitment: 20+ hours annually researching, monitoring, rebalancing

Analysis:

  • ETF delivers $1,100,000 for minimal work
  • Mutual fund delivers $860,000 (same work as ETF, worse outcome)
  • Stock picking delivers $1,230,000 if you're skilled; if you're average, you underperform ETFs by 1% (the average investor's fate)

The math favors ETFs for 95% of investors. Stock picking is only rational if you have genuine edge—which is rare. The Rule of 72 exposes this: a 1% fee difference costs 20% of final wealth. You must outperform by more than 1% every year just to justify the active-management approach.

Comparing alternative investments: Private equity vs. public stocks​

Scenario: Access to a private-equity fund with 15% expected return vs. S&P 500 with 10%.

Private equity​

  • Expected return: 15% annually
  • Doubling time: 4.8 years
  • Doublings in 30 years: 6.25 ≈ 76×
  • Expected final value: $100,000 × 76 = $7,600,000
  • Reality check: Survivorship bias inflates reported returns. True returns (including failed funds) average 11–12%.
  • Lockup period: 7–10 years; you can't access capital
  • Minimum investment: Often $250,000–$1M, excluding smaller investors

S&P 500​

  • Expected return: 10% annually
  • Doubling time: 7.2 years
  • Doublings in 30 years: 4.17 ≈ 18×
  • Final value: $100,000 × 18 = $1,800,000
  • Liquidity: You can sell any trading day
  • Minimum investment: $1 (via fractional shares)

Comparison:

  • Private equity headline: $7.6M vs. $1.8M (4.2× advantage)
  • Private equity reality (adjusted for bias): ~$2.1M (slightly better than S&P 500)
  • Private equity after fees (typically 2% + 20% of gains): Maybe $1.6M (worse than S&P 500)
  • Private equity liquidity: Locked up 7–10 years (opportunity cost if you need capital)

Conclusion: Private-equity marketing emphasizes headline returns while hiding fees, survivorship bias, and illiquidity. The Rule of 72 reveals the true picture: for most investors, public stocks offer better risk-adjusted returns with full liquidity. PE is only suitable if you have dedicated capital you won't need, can tolerate illiquidity, and believe the manager has genuine edge (rare).

The power of a decision tree: Choose based on goals and time​

Real-world comparison example: Choosing between two jobs​

Job A: $120,000 salary, 3% 401(k) match
Job B: $110,000 salary, 6% 401(k) match

Both careers last 35 years to retirement.

Job A analysis​

  • Salary advantage: $10,000/year × 35 = $350,000 cumulative
  • Cumulative match: $120,000 × 0.03 × 35 = $126,000
  • Match compounding (8%, doubling 9 years): 35 ÷ 9 = 3.9 doublings ≈ 14× multiplier
  • Final match value: $126,000 × 14 = $1,764,000
  • Plus salary advantage (can be invested separately): $350,000 × 7.5× (at 8% for 35 years) = $2,625,000
  • Total wealth creation: ~$4.4M

Job B analysis​

  • Salary disadvantage: −$10,000/year × 35 = −$350,000
  • Cumulative match: $110,000 × 0.06 × 35 = $231,000
  • Match compounding (8%): 35 ÷ 9 = 3.9 doublings ≈ 14×
  • Final match value: $231,000 × 14 = $3,234,000
  • Less salary disadvantage (reduces investments): −$2,625,000
  • Total wealth creation: ~$600,000

Job A is worth $3.8M more in retirement wealth due to the larger salary base. The higher match in Job B doesn't compensate—it's a trap. This reversal reveals that salary often matters more than benefits once benefits are compounded properly.

Common mistakes when comparing investments​

Mistake 1: Using pre-tax returns. Always adjust for taxes. A 10% stock return becomes 8.5% after 15% long-term capital gains tax. See Common Rule-of-72 Mistakes for a deeper analysis of this and other errors.

Mistake 2: Ignoring fees. A 1% fee costs 20% of final wealth. This compounds silently; many investors don't notice until comparing statements decades later.

Mistake 3: Comparing time horizons unevenly. Bonds beat stocks for <5-year goals; stocks beat bonds for 20+ years. Comparing them across different timescales is apples-to-oranges.

Mistake 4: Assuming past returns predict future returns. A fund that earned 15% for 5 years won't earn 15% forever. Revert to mean-return assumptions (10% for stocks, 5% for bonds).

Mistake 5: Chasing headline returns. Private equity, crypto, and micro-caps advertise spectacular returns. Adjust for survivorship bias, selectivity bias, and fees. The Rule of 72 reveals whether headline numbers are realistic. Use mental-math shortcuts to quickly reality-check claims.

FAQ​

Q: Should I compare investments before or after taxes?
A: Always after taxes. Comparing pre-tax returns is like comparing salaries without knowing tax rates. Context is mandatory.

Q: How often should I re-compare my investments?
A: Annually during tax planning. Quarterly or monthly comparisons are noise; markets fluctuate. Strategic reallocation should happen yearly, at minimum.

Q: Is a 1% difference in return rate worth changing investments?
A: Yes, if you're investing $100K+. The Rule of 72 shows that 1% costs 10–15% of final wealth over 25+ years. If fees or performance are controllable (switching to lower-cost funds), it's a high-probability win.

Q: What if two investments have the same doubling time but different volatility?
A: Choose lower volatility. You'll reach the same destination with less stress. Volatility doesn't create returns; it just makes the journey bumpy. Unless volatility is temporary and you can ignore it (stay invested), lower volatility wins.

Q: Can I use Rule of 72 to compare investments from different countries?
A: Yes, but adjust for currency risk. A 10% return in euros is only valuable if the euro strengthens relative to your home currency. Currency fluctuations can wipe out return advantages.

Q: Should I compare gross return or net (after all fees and taxes)?
A: Always net. Gross is marketing; net is reality. A 10% gross return with 2% fees and 15% taxes becomes 6.5% net—very different decision.

  • Doubling-Time Table for Common Rates — Reference for exact doubling times across all returns
  • Mental-Math Tricks Built on the Rule of 72 — Speed techniques for quick comparisons
  • Asset allocation — How to blend investments for optimal risk-adjusted returns
  • Fee impact on returns — Why expense ratios and trading costs compound
  • Tax-loss harvesting — Strategies to reduce tax drag when comparing investments

External authority resources:

Summary​

Comparing investments using the Rule of 72 means calculating doubling times for each option, adjusting for fees and taxes, then projecting final wealth over your time horizon. Stocks double every ~7 years (10% historical return) vs. bonds every ~14 years (5% return); over 30 years, this 7-year gap compounds into roughly 3.7× more wealth from stocks. Fees and taxes are invisible wealth killers—a 1% annual fee costs 20% of final wealth; taxes reduce returns by 25–35% depending on account type. Time horizon is critical: bonds win for <5-year goals; stocks dominate for 20+ years. Real-world comparisons must subtract inflation (2–3%) and account for volatility (stocks offer higher returns but are less predictable). Using the Rule of 72 to compare investments transforms vague promises ("excellent returns") into concrete numbers (doubling time, wealth projection), enabling disciplined choice-making based on math rather than marketing.

Next​

For warnings about Rule-of-72 mistakes, read Common Rule-of-72 Mistakes.