Compound return measures the total growth of an investment including the effect of reinvesting all earnings — dividends, interest, and capital gains. Unlike simple return which adds gains linearly, compound return reflects the exponential growth that occurs when returns generate their own returns. It is the single most important metric for evaluating long-term investment performance, and understanding it deeply changes how you think about wealth-building, risk, and time.
A 10% annual compound return means each year's gain is calculated on the previous year's ending balance, not the original investment. Year 1: $10,000 → $11,000. Year 2: $11,000 → $12,100 (not $12,000). Year 3: $12,100 → $13,310. The extra $310 beyond $13,000 is the compounding effect — returns earning returns. Over 30 years, that same 10% annual compound return turns $10,000 into $174,494. Simple interest at 10% would produce only $40,000. The difference — $134,494 — is created entirely by compounding. This is why Albert Einstein famously referred to compound interest as the eighth wonder of the world.
Compound return also reveals the destructive power of losses. A 50% loss requires a 100% gain to recover — not 50%. This asymmetry means avoiding large losses is mathematically more important than capturing large gains. A portfolio that earns 10% per year steadily will outperform one that alternates between +30% and -10%, even though the simple average is the same (10%), because the volatility creates "volatility drag" on compound returns. The sequence of returns matters enormously in the compounding equation.
Volatility drag is the silent tax on compound returns. The mathematical relationship between arithmetic return (simple average) and geometric return (compound return) is: Geometric Return ≈ Arithmetic Return − (Variance ÷ 2). A portfolio with an arithmetic average return of 10% and annual standard deviation of 20% has a compound return of approximately 8% — 2% lower than the average. This means two funds with identical average returns but different volatility will produce different wealth outcomes over time. Lower volatility doesn't just feel better; it mathematically produces higher compound returns.
The Compound Annual Growth Rate (CAGR) is the standard way to express compound return. CAGR answers the question: "At what constant annual rate would an investment have grown from its starting value to its ending value?" CAGR = (Ending Value / Beginning Value)^(1/Years) − 1. A portfolio that grew from $50,000 to $150,000 over 10 years has a CAGR of (150,000/50,000)^(1/10) − 1 = 11.6%. This single number summarizes the full compounding effect over the entire period, regardless of the ups and downs along the way.
Sequence of returns risk is compound return's most dangerous feature for retirees. During the accumulation phase, volatility hurts compound returns but time mitigates the damage. During the withdrawal phase, a severe bear market in early retirement can permanently impair a portfolio — because withdrawals force selling at depressed prices, leaving less capital to participate in the eventual recovery. A retiree who experiences -30% in year 1 and then withdraws 4% annually is in a fundamentally worse position than one who experiences the same average return with the 30% down year occurring in year 15. Managing sequence of returns risk is why asset allocation shifts toward bonds near and in retirement.
Reinvestment is what separates compound return from total return in practice. When dividends or interest are paid but not reinvested, the portfolio earns simple interest on that cash. True compounding requires that every dollar of income be reinvested immediately into the portfolio. Dividend reinvestment plans (DRIPs) automate this. Studies consistently show that dividends reinvested account for the majority of the S&P 500's long-term total return — from 1960 to 2023, reinvested dividends contributed approximately 40% of the index's total compound return. The investor who takes dividends as cash rather than reinvesting forfeits an enormous portion of the compound return available to them.