Frequently Asked Questions
Common questions about backtesting ETFs and stocks with dollar-cost averaging: how the simulation works, how dividends and returns are handled, where the data comes from, and what the results do and don't tell you.
#Getting started
What does ETF Stock Calculator do?
It backtests a dollar-cost averaging (DCA) plan across up to 10 ETFs or stocks at once using real historical daily prices. You set an initial investment, a recurring contribution and schedule, and a time period; the tool simulates the plan day by day and shows what each position would be worth today, side by side.
Do I need to create an account?
No. The tool is completely free and requires no sign-up, no email, and no download. You enter your tickers and parameters, click Run Comparison, and see results immediately.
Is this financial advice?
No. ETF Stock Calculator is an educational and research tool. It shows historical, pre-tax, idealized results for the exact plan you enter. Past performance does not predict future results, and nothing here is a recommendation to buy or sell any security. Always consult a qualified financial advisor before investing.
How many tickers can I compare at once?
Up to 10 ETFs or individual US-listed stocks in a single comparison. You can mix ETFs and stocks freely, for example comparing VOO, QQQ, and AAPL together on the same chart.
How do I see the breakdown of contributions vs. gains?
Two ways. First, hover anywhere on the portfolio value chart. The tooltip shows each ticker's total value, plus a second line breaking it down into amount contributed and gains (or loss). Second, click any ticker name in the chart legend to open a stacked contributions-vs-gains area chart for just that ticker, showing how the two components grew over the full simulation period. Click the same ticker again, or the '✕ close' button, to dismiss it.
#Dollar-cost averaging
What is dollar-cost averaging (DCA)?
Dollar-cost averaging means investing a fixed amount on a regular schedule, for example $500 every month, regardless of the current price. You automatically buy more shares when prices are low and fewer when they're high, which smooths your average purchase cost over time and removes the temptation to time the market. This tool backtests exactly that behavior.
Can I test a one-time lump sum instead of recurring contributions?
Yes. Set the contribution frequency to 'Lump sum' and the simulation invests only your initial amount at the start, with no recurring buys. This is useful for comparing a single upfront investment against a steady contribution plan for the same ticker and period.
What contribution schedules are supported?
Weekly (every 7 days), monthly (every 30 days), quarterly (every 91 days), annually (every 365 days), or a one-time lump sum. The scheduler advances by a fixed interval after each buy, so a 10-year monthly plan always produces exactly 120 contributions plus the initial investment.
Can I compare real ETFs against a hypothetical fixed return?
Yes. Click '+ Add benchmark rate' in the Tickers panel and enter any annual percentage. The tool adds a 'Fixed X% Return' line to the chart and table alongside your real tickers, showing exactly what the same contribution plan would be worth at that steady rate. This is useful for benchmarking VOO against a 7% target, modeling a savings account yield as an opportunity cost, or simply asking whether the stock market beat a boring fixed-rate alternative over your chosen period. The benchmark is computed locally in the browser, with no extra network request, and is a purely hypothetical instrument with no volatility, fees, or taxes.
#Dividends, returns, and the math
Does the calculator reinvest dividends?
You choose. With DRIP (dividend reinvestment) on, each dividend immediately buys additional fractional shares at that day's price, and those shares earn future dividends themselves. With DRIP off, dividends accumulate as a separate cash balance that's added to your final portfolio value. Dividends are never ignored or double-counted either way.
Why is the annualized return different from a simple (final ÷ invested) calculation?
The annualized return shown is IRR (internal rate of return), not simple CAGR. For a contribution plan, IRR is more accurate because it accounts for how long each dollar was actually invested: your first contribution may have compounded for ten years while your last one was invested for only a few weeks. Simple CAGR ignores that timing and can badly over- or understate the true rate.
What is IRR, in plain terms?
IRR is the single constant annual growth rate that would produce your final balance given the exact timing of every contribution. If every dollar you invested had earned that one rate from the moment it went in, you'd end up with the same amount you actually did. It's the fairest single number for comparing DCA plans of different shapes.
Does it account for stock splits?
Yes. All calculations use the adjusted close price, which retroactively corrects for splits. A 4-for-1 split doesn't show up as a false 75% price drop; the history stays continuous so your simulated share counts and values remain correct.
Are ETF expense ratios included?
Yes, implicitly. An ETF's expense ratio is already deducted from its net asset value and therefore baked into the adjusted close price history. No separate fee needs to be subtracted; the annual drag is already reflected in the prices the simulation uses.
#Data and accuracy
Where does the historical data come from?
Price and dividend data is pulled live from Yahoo Finance each time you run a comparison, at daily resolution. For each ticker the simulation receives daily open/high/low/close, the adjusted close, dividend events, and volume.
How accurate are the results?
The simulation itself is exact. It uses every real trading day with no interpolation. The main caveats are the data source (Yahoo Finance is reliable for major ETFs and US stocks but can have gaps for thin or international securities), the use of closing prices rather than intraday execution prices, and the fact that taxes are not modeled. Results represent a pre-tax, idealized scenario that most closely matches a tax-advantaged account like an IRA or 401(k).
What happens if a fund didn't exist for the whole period I chose?
The simulation detects the ticker's actual inception date and starts from there instead, flagging the result as having insufficient history. That way a newer fund is never unfairly compared against a longer track record, since all of its metrics reflect the shorter actual period it was available.
Does it model taxes?
No. Dividend income and capital gains taxes are not deducted, since they depend on your account type, income, and holding period. Results are pre-tax. A tax-advantaged account (IRA, 401(k), Roth) would track the simulation most closely; a taxable brokerage account would see some drag from taxes on dividends and realized gains.
#AI interpretation
What does the AI analysis do?
After a comparison, you can optionally send a structured summary of your results to Claude (Anthropic) for a plain-English interpretation: what the numbers mean, how the instruments compared, and what likely drove the differences. It's generated once per run, has no memory between runs, and is not financial advice.
Why is the AI analysis sometimes rate-limited?
The AI feature costs money to run, so it's rate-limited per user to keep the tool free. It's an optional extra. Your full numerical results, chart, and table are always available without it.