ETF Calculator, Backtest an ETF Investment

2. Important Information

This calculator uses real historical price data, but historical performance is not a guarantee of future results. Markets that grew over the period you select may not grow the same way going forward and past downturns don't predict future ones either. Nothing on this page is financial, investment, or tax advice; it's a tool to help you understand how investments have behaved historically, not a recommendation to buy any specific fund. Use it to inform your own thinking, not to replace it.

3. Example ETF Investment

Scenario: $10,000 initial investment in VOO (Vanguard S&P 500 ETF), plus $1,000 added every month for 10 years, from August 2016 through August 2026, with dividends reinvested.

4. Understanding Your Results

Investment Summary

• Final Investment Value: what the entire investment (initial plus contributions) is worth at the end of your selected period.
• Total Earnings: the portion of that value that came from market growth, separate from money you put in yourself.
• Dividends Received: the total dividend payments the investment received over the period. When dividends are reinvested, this amount is already included in Final Investment Value and Total Earnings; when taken as cash, it's tracked here separately from Balance.
• Initial Balance: your starting lump sum.
• Additional Deposits/Withdrawals: the running total of any recurring contributions (or withdrawals) over the period.

Results table

Each row is one month (or one contribution period, if you've chosen quarterly or annual contributions). Deposits/Withdrawals shows that month's transaction, Total Deposits/Withdrawals is the running sum, Earnings is that month's market gain or loss, and Balance, the final column, is the running total value of the investment at that point. If you've chosen "Taken as cash" for dividends, an extra Dividends column appears showing that month's payment; when dividends are reinvested instead, their effect is already reflected in Balance's growth, so the column doesn't appear.

Total Balance

A line chart showing your balance for every month in the period, so you can see the shape of the growth over time, not just the final number.

Deposits vs. Earnings

A stacked area chart showing how much of your balance came from your own contributions versus market growth. The earnings layer is green if the investment ends the period positive, red if it doesn't.

5. Historical Data & Methodology

• Data granularity: monthly, not daily. Every price used is the closing price for that month, normalized to the first of the month for consistency across funds.
• Dividends: reinvested or cash. Every calculation starts from the fund's raw closing price plus its real dividend payments and stock splits, the same underlying data either way. By default, dividends are reinvested: each payment is used to buy additional shares of the fund at that month's price, so future dividends are then paid on a larger share count too. Switching to "Taken as cash" skips that step, the same dividend cash is tracked separately in a running total instead of buying shares. The two scenarios can end quite differently, that's the effect of compounding reinvested dividends over time, not a rounding difference.
• Fees: a fund's expense ratio is deducted continuously from its own assets, so it's already reflected in the price itself, unlike dividends, which require the adjustment described above. The calculator doesn't show or let you compare fee drag explicitly, though.
• What's not adjusted for: inflation and taxes are not factored in anywhere. Every number shown is a nominal figure.
• Data coverage: if the date range you select goes back further than a fund's actual price history, the calculation automatically adjusts to the earliest available data and tells you so, rather than failing or silently guessing.

We use monthly (rather than daily) data because it's the right level of precision for the question this tool answers, "how would a long-term investment have grown," without the noise of day-to-day price swings.

6. How to Use Historical Backtesting

Backtesting is a starting point for understanding how an investment has behaved, not a prediction of how it will behave. A few habits make the results more useful:

• Test long time periods, not just the last few years. A 3-year window can look very different from a 20-year one, especially if it happens to skip a downturn.
• Try more than one starting point. Use the date-range presets to see how the same ETF performed starting before and after the 2008 financial crisis, or before and after the 2020 COVID crash. If the results remain informative across several different starting points, you get a better picture of how the strategy behaved across different market environments.
• Watch for overfitting to a single window. It's tempting to find the exact start date that produces the best-looking number, but that's picking the answer you want, not learning something real about the investment.
• Compare contribution styles. Try the same ETF as a lump sum and again as a monthly contribution, to see how differently the two approaches play out over the same period.

7. Understanding Long-Term Compound Growth

Compound growth means your gains start generating their own gains, and that effect gets stronger the longer it runs. A contribution made in year one has decades to compound if you're investing for retirement; a contribution made in year nineteen has almost none. That's why the length of the time period you test often matters more than which specific ETF you choose.

8. What the Calculator Can and Cannot Tell You

It can show you:

• How a specific ETF actually performed over a specific historical period, including the effect of dividends being reinvested (or taken as cash, if you toggle that).
• How lump-sum investing compares to spreading contributions out over time, using real historical prices.
• How sensitive an outcome is to when you started, by testing multiple date ranges yourself.

It cannot tell you:

• What any ETF will do in the future. Every result here is historical.
• The full effect of fees. A fund's expense ratio is deducted continuously from its own assets, so it's already baked into the price itself, not something we add in the way dividend reinvestment is. But there's no separate fee input or fee-drag comparison shown, so you can't isolate how much a fund's fees cost you versus a lower-cost alternative.
• Real, inflation-adjusted purchasing power. All figures are nominal: a dollar (or pound, or euro) at the end of the period is treated the same as one at the start, even though it buys less.
• Tax consequences. Capital gains, dividend tax treatment, and account type (ISA, 401(k), taxable brokerage, etc.) all affect your real return and aren't modeled here.
• Broker or platform costs. Trading commissions, platform/custody fees, and FX conversion charges from your own broker are separate from the fund's expense ratio and aren't factored in. Those depend on which broker you use, not on the ETF itself.

Want to model more than one ETF at a time instead of a single fund? The ETF Portfolio Calculator lets you combine several with your own allocation and backtest the mix together.

9. Frequently Asked Questions