Backtesting
What past prices can tell you before you invest, and what they can'tA backtest replays history. You pick an amount, a start date and one or more stocks or ETFs, and it works out what that money would be worth today if you had invested it back then.
It can't predict the future. What it can show you is what holding the investment was like: how far it fell along the way, and how much a monthly plan would have changed the result.
The free Backtest calculator compares up to five stocks, ETFs or indexes side by side, with a one-off or a monthly investment. No account needed.
When a backtest is useful
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Choosing between funds
Two world ETFs with different fees or index providers can look alike on paper. Run them over the same years and you can see how far apart they ended.
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Deciding between a lump sum and a monthly plan
Run the same amount once and every month. Investing all at once usually ends higher when markets rise. A monthly plan does better when they fall soon after you start.
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Testing your nerves
The worst drop tells you how far the investment fell from its peak. If seeing your money down 35% would make you sell, the investment is too risky for you, whatever its long-term return.
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Setting realistic expectations
A yearly return over 15 or 20 years is a better guide than last year's headline number.
How to use the Backtest calculator
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Enter an amount and how often.
Choose once for a single investment on the start date, or every month to invest the same amount every month on the same day as the start date, or the next trading day.
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Add up to five securities.
Search by name, symbol or ISIN. Adding an index such as the S&P 500 gives you a benchmark to compare against.
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Pick a start date.
Longer periods tell you more. To see how an investment held up through a crash, start just before one, such as early 2008 or early 2020.
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Read the results.
For each security you get what you put in, what it is worth now, the gain and the total return, plus:
- Worst drop: the largest fall from a peak to a later low over the period.
- Per year: the average yearly return on your money, taking the timing of each monthly purchase into account. It is shown for periods of a year or more.
A backtest shows the one path prices happened to take. Results are in euros, so currency moves are included, but broker fees and taxes are not. Funds that pay out their dividends may look worse than accumulating ones that reinvest them, so compare share classes of the same kind.