Portfolio backtester: how would every allocation of your ETFs have performed — after costs and taxes?

A backtest uses historical prices to work out how an investment would have performed. Paperball does this not for one allocation but for every allocation of your securities at once — that counts as one backtest, whether it is 50 or 50,000 allocations.

A backtest looks back: it uses real prices to work out what would have become of your money — exactly as things turned out at the time. That gives a single path. The Monte Carlo simulation asks one question more: what if the good and the bad years had come in a different order? To find out, it cuts the real price history into pieces of twelve months each and puts them back together 10,000 times. That shows you how differently things could have gone — for example, in how many of these paths your withdrawals would have lasted to the end. In short: the backtest shows what happened; Monte Carlo shows the range. Neither is a forecast.

ETFs, funds and stocks with a price history. On every plan you choose freely from more than 80,000 securities, found by ISIN or symbol, or upload prices from a file.

As long as all selected securities have prices in common, at least one year. If that is less than five years, Paperball points it out and names the security that shortens the period. If you like, you calculate only the most recent years.

A backtest needs at least one year, a Monte Carlo simulation at least five years in which all selected securities have prices. If that is not enough, there are two possible reasons. First: the security is simply still young. If an ETF was launched three years ago, there are only three years of prices — nobody can extend them. For the calculation you can then use an older security with similar holdings, for example another ETF on the same index. Second: the security is older, but our data provider does not deliver its prices far enough back. Then you add the missing prices yourself: on the “Watchlist” page, upload a price file (CSV) for the security — this is available on every plan. Tip: you can find free prices at onvista.de and investing.com. With a free account you can download the historical prices there as a CSV file, and Paperball reads both formats directly.

Order fees on purchase and on every rebalancing trade, the front-end load per security and an annual custody fee if you enter one. A fund's ongoing charges (TER) are already reflected in its price. Paperball does not model spreads separately — if you want to account for them, add them to the percentage order fee.

Only if you choose to. By default distributions are left out: they are shown as a metric of their own, and return and final value measure price performance. In the form you can reinvest them instead — on the ex-dividend date, after tax, into the same security, as with an accumulating fund. The ex-dividend date is the first trading day on which the security trades without entitlement to the distribution. With a savings or withdrawal plan, they can also pay the withdrawals or go into the liquidity buffer.

Paperball knows the mechanics of 8 countries: tax on capital gains and distributions, partial exemption, allowances, wealth tax and, in the US, the holding period. Paperball does not maintain the rates itself — you enter them or use sample values. The result is an approximation and does not replace tax advice.

No. Paperball is a calculation tool and does not provide investment advice or investment recommendations. A backtest recalculates how an allocation would have performed in the past. The results are calculated in hindsight and are not a reliable indicator of future performance. You make decisions about your investments yourself.

Yes. The portfolio backtest and the Monte Carlo simulation belong to the same account and the same plans. Getting started is free for good — see all prices.