ETF Return Calculator - Compound Growth, Savings Comparison and Inflation

Compound interest turns small monthly payments into six-figure portfolios

The math is straightforward: $500/month invested in an ETF averaging 8% annual return for 20 years becomes $294,510. Your total contributions? $120,000. The remaining $174,510 is compound growth - money your money earned. This calculator runs the future value formula with monthly compounding, compares the result against a savings account, and adjusts for inflation so you see both the nominal and real purchasing power of your portfolio.

How to use this calculator - step by step

Initial investment - enter a lump sum if you have one. Enter 0 to model pure monthly contributions.
Monthly contribution - the fixed amount you invest each month. Even $100/month compounds significantly over decades.
Expected annual return - use historical averages: S&P 500 ~10%, MSCI World ~8%, bond ETFs ~3-5%.
Investment period - enter the number of years. 10 years is the minimum for equity ETFs.
Savings account rate (optional) - enter a rate to compare ETF returns against a low-risk alternative.
Inflation (optional) - enter expected annual inflation to see real purchasing power.

The formula behind the numbers

    FV = PV x (1 + r)n + PMT x ((1 + r)n - 1) / r
  

Where: PV = initial investment, PMT = monthly contribution, r = monthly rate (annual / 12), n = total months.

The first term compounds your lump sum. The second term compounds each monthly payment for its remaining duration. Together, they produce the future value with both one-time and recurring investments.

ETF vs savings account - scenario comparison

Monthly contribution: $500, savings rate: 4.5%, ETF return: 8%.

Period	Contributions	ETF (8%)	Savings (4.5%)	ETF advantage
5 years	$30,000	$36,738	$33,625	+$3,113
10 years	$60,000	$91,473	$75,599	+$15,874
20 years	$120,000	$294,510	$192,048	+$102,462
30 years	$180,000	$745,180	$382,819	+$362,361

At 5 years, the gap is modest. At 30 years, the ETF portfolio is nearly double the savings account. That is the compounding curve - slow at first, then exponential.

Historical average returns by ETF type

ETF / Index	10-year avg	20-year avg	Notes
S&P 500 (VOO, SPY)	~12%	~10%	500 US large-cap companies
MSCI World (IWDA)	~10%	~8%	1,500+ companies, 23 countries
MSCI Emerging Markets	~5%	~6%	Higher volatility, higher potential
US Aggregate Bond (AGG)	~2%	~3%	Low risk, low return
Total World (VT)	~9%	~7%	Entire global stock market

Practical examples

Example 1: $200/month, 30 years, MSCI World (8%)
Contributions: $72,000 - Portfolio: $298,072 - Gain: +$226,072 (314%)

Example 2: $10,000 initial + $1,000/month, 25 years, S&P 500 (10%)
Contributions: $310,000 - Portfolio: $1,443,036 - Gain: +$1,133,036 (365%)

Example 3: $50,000 lump sum, no monthly, 20 years, 8%
Contributions: $50,000 - Portfolio: $233,048 - Gain: +$183,048 (366%)

Example 4: $500/month, 20 years, 7% vs 9% - the 2% gap
At 7%: $260,464 - At 9%: $334,885 - Difference: $74,421

Example 5: $300/month, 15 years, bond ETF (3%) vs equity ETF (8%)
Bond: $68,188 - Equity: $104,680 - Equity adds: +$36,492

FAQ - Frequently asked questions

Does this calculator account for taxes?

No - results are pre-tax. Capital gains tax applies when you sell ETF shares. In the US, long-term capital gains (held 1+ year) are taxed at 0%, 15%, or 20% depending on income. Tax-advantaged accounts (401k, IRA, Roth IRA) can eliminate or defer this tax entirely.

What return rate should I use?

Historical averages: S&P 500 ~10%, MSCI World ~8%, emerging markets ~6%, bonds ~3%. For conservative planning, subtract 1-2 points. Run multiple scenarios (optimistic, baseline, pessimistic) to see the range of outcomes.

What if the market crashes 40%?

This calculator uses a constant average return. In reality, some years return +25%, others -30%. Historically, the S&P 500 has recovered every crash within 3-5 years. With a 15+ year horizon, annual fluctuations average out. If you are contributing monthly, crashes actually help - you buy more shares at lower prices.

Is it better to invest a lump sum or dollar cost average?

Statistically, lump sum investing beats DCA about two-thirds of the time because markets trend upward. But DCA reduces the risk of investing everything at a market peak. For most people, DCA through monthly contributions is the practical choice - you invest as you earn.

How does the expense ratio (TER) affect returns?

The expense ratio is deducted from your return. An ETF returning 8% with a 0.20% TER gives you 7.80% net. Over 20 years on $500/month, the difference between 0.07% TER (Vanguard VOO) and 1.00% TER (active fund) is roughly $40,000. Low-cost index ETFs win.

Can I start with a small amount?

$100/month at 8% for 30 years grows to $149,036. Your contributions: $36,000. The rest is compound growth. Time matters more than amount. Starting 10 years earlier with $200/month beats starting later with $500/month.

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