Build your own ETF
Finisdom’s Fund Foundry lets you invent an index the way a fund manager does: pick the members and weights, set a cash sleeve and a rebalance cadence, and watch the rule run through real history — with each holding joining only from the date it genuinely existed. Publish it and the rule freezes, the backtested claim is stored permanently, and a live record starts that day.
What it does
- Build a fund as a rule — members, relative weights, cash sleeve, rebalance cadence
- Point-in-time cohort simulation: holdings join only once they actually existed
- Decades-long windows where a naive backtest of the same tickers would allow a few years
- The factor genome — Fama-French 5 plus momentum, with Newey-West standard errors
- Effective bets: how many independent risks you hold, not how many tickers
- Sharpe struck against the real 3-month T-bill, on both the claim and the live record
- Publishing freezes the rule and fingerprints it — the claim can never be quietly restated
- A public leaderboard that ranks on kept promises rather than returns
How it works
Write the rule
Choose members and relative weights, a fixed cash sleeve, and how often it rebalances. Weights are ratios, so the rule stays coherent in years when only half the members existed.
Replay it point-in-time
Each member is treated as a lifespan rather than a column — it joins the fund the day it became investable. That is what lets a rule run for thirty years even when its youngest holding listed five years ago.
Read the genome before you publish
The simulated curve is regressed against the Ken French factor set. If the genome says your six-holding idea is one large momentum bet, the backtest is telling you about a factor rather than about your idea.
Publish, and let it be judged
The rule freezes and the backtested figures become a permanent claim. From that day the Decay Board compares the claim against what the same rule actually delivers — and a fund can be retired, but never deleted.
Frequently asked
Can I really build my own ETF?
You can build and publish the rule that defines one, simulate it across decades of real prices, and carry a public track record for it. What you cannot do here is launch a regulated, tradeable fund — that requires a sponsor, a custodian, an exchange listing and regulatory approval. This is the design and evidence layer, not a brokerage.
How is this different from a normal portfolio backtester?
A backtester answers "how would these tickers have done". The Foundry treats the fund as a rule with a lifecycle: members join point-in-time as they become investable, the rule is fingerprinted and frozen at publication, the backtested claim is stored and never recomputed, and a live out-of-sample record starts the same day. The backtest is the hypothesis; the record after publication is the evidence.
What is a factor genome?
A fund’s returns regressed against the Fama-French five factors plus momentum, expressed as the annualised volatility each factor contributes. It answers what a fund is actually exposed to rather than what it happens to hold — two funds with completely different tickers frequently turn out to be the same handful of genes.
What are effective bets?
How many genuinely independent risk exposures a portfolio carries. It is almost always far smaller than the number of holdings: four well-known US equity ETFs measure about 1.76 effective bets, because the market factor is present in all four at 100% of the book. Counting tickers overstates diversification; counting effective bets does not.
Why does the leaderboard rank on kept promises instead of returns?
Because ranking on returns just surfaces whoever took the most risk in the luckiest window, and a board that quietly dropped its failures would be a survivor list. Ranking on retention — the share of the backtested claim the fund actually delivered after publication — asks the only question a backtest cannot answer for itself.
Can I edit a fund after publishing it?
No. The rule freezes permanently at publication, which is the constraint the whole record rests on. Changing your mind forks a new fund that starts its own record from zero, so a track record always belongs to the rule that earned it.
How long before a published fund means anything?
Roughly six months before the numbers say anything at all, and a couple of years before they say much. Anything younger is reported as too new to read rather than as good or bad — a confident figure over six weeks would be noise dressed as insight.
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Backtests and optimizations are hypothetical illustrations built from historical data — not predictions, and not investment advice. Past performance does not guarantee future results.