Double – Design and invest in your own stock index
Hey everyone, we’re JJ and Mark from Double (https://double.finance). Over the past few months we’ve been working on an investing app that lets anyone design and invest in their own stock index. Start by picking one or more strategies. You can find 20+ starting points in Double that vary from direct index versions of classic ETFs (like SPY) to strategies focused on specific industries, market trends, or themes (like YC public companies). You can also easily build your own grouping of stocks, and tilt your strategy towards or away from certain stocks or sectors. Once you’ve chosen…
In plain words
Double is an investing app that lets users design and invest in custom stock indexes. It offers over 20 pre-built strategies ranging from direct index versions of classic ETFs to themed portfolios focused on industries or trends, plus the ability to build entirely custom stock groupings. The app handles daily portfolio optimization, automatically managing trades while accounting for taxes and trading costs, and enables tax loss harvesting for sufficiently diversified accounts.
written from the facts on this page · September 2026
From the sources
In the maker’s words, at launch
Hey everyone, we’re JJ and Mark from Double (https://double.finance). Over the past few months we’ve been working on an investing app that lets anyone design and invest in their own stock index. Start by picking one or more strategies. You can find 20+ starting points in Double that vary from direct index versions of classic ETFs (like SPY) to strategies focused on specific industries, market trends, or themes (like YC public companies). You can also easily build your own grouping of stocks, and tilt your strategy towards or away from certain stocks or sectors. Once you’ve chosen your portfolio, we run a daily portfolio optimization to determine what trades to make, which considers taxes, trading costs, drift and holding costs[1]. If your account is sufficiently diversified, we enable Tax Loss Harvesting as well to capture losses that can help offset capital gains[2]. Finally you can move between strategies either all at once or over time[3]. JJ started work on this after selling his last company, making some money, and growing really frustrated at the quality of the portfolio tools available to retail investors. Financial advisors have tools for direct indexing, tax loss harvesting and dollar cost averaging, but they generally charge upwards of 1% a year in AUM fees. Things like Parametric[4] and Canvas[5] have succeeded, but are only accessible through advisors. We wanted to build these kinda advanced portfolio tools for ourselves without any AUM fees. Some common use cases we’ve found are diversifying away from a large RSU position or migrating between risk on and risk off strategies over time. You can also easily allocate a percent of your portfolio to specific baskets of stocks. Let us know what you think! Feel free to email us at [email protected] as well [1] More info about our optimizer here https://help.double.finance/en/articles/9718142-portfolio-op... [2] More info about out direct indexing tax loss harvesting here https://help.double.finance/en/articles/9718959-direct-index... [3] More info about out dollar cost averaging here https://help.double.finance/en/articles/9718389-dollar-cost-... [4] https://www.parametricportfolio.com/ [5] https://canvas.osam.com/
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