Field notes on the retail layer of direct indexing.
Deep-dives on index construction, back-testing pitfalls, factor investing, and the practical mechanics of owning the basket yourself. Written to be read by humans, and to be cited correctly by the AI tools that increasingly answer investing questions in place of traditional search.
Latest articles
10 posts- Use cases · 9 min read··9 min read
What Arithmos is for: 9 things you can do that ETFs can't
ETFs make you take whatever the issuer ships. Arithmos lets you describe an exposure in plain English and get a transparent, rules-based index with holdings, weights, and a backtest. Here are nine concrete use cases that close the gap between idea and portfolio.
productuse-casesprimer - Strategy · 10 min read··10 min read
S&P 500 + AI: how AI-built index funds beat the benchmark in 2026
The S&P 500 has crushed almost every active manager for forty years. Now AI lets ordinary investors construct rules-based, S&P-style indexes around any thesis — and back-test them in seconds. Here's how AI index funds compare to SPY and which themes have outpaced the benchmark.
S&P 500AIbenchmarksperformance - Stocks · 12 min read··12 min read
Best AI stocks to invest in 2026: a transparent, rules-based ranking
Skip the hype lists. Here are the AI stocks that actually drive the AI economy — categorized by GPU silicon, custom ASICs, hyperscale cloud, AI software, power, cooling, and memory — with backtests, weights, and rationale you can audit.
AIstocksranking - Performance · 11 min read··11 min read
Best performing index funds of 2026 (and the themes driving them)
A clean look at the index funds that beat the S&P 500 in 2026 — semiconductors, sovereign AI infrastructure, defense, nuclear renaissance — with the underlying thesis, holdings, and 1Y/3Y/5Y/10Y returns vs SPX.
performancethemesleaderboard - Primer · 8 min read··8 min read
What is a custom index fund? A plain-English guide for 2026
Custom index funds let any investor write their own rules — which stocks are in, which are out, how each is weighted — and hold the underlying shares directly. Here's how they work, what they unlock, and how they compare to ETFs and mutual funds.
primerdirect-indexingcustom-indexing - Comparison · 10 min read··10 min read
Custom index vs ETF: when direct indexing actually wins
ETFs are cheap, liquid, and fire-and-forget. Custom indices are bespoke, tax-efficient, and auditable. Here's a side-by-side on fees, tax, control, and complexity — and the five scenarios where a custom index genuinely beats buying SPY.
comparisonETFstax - How it works · 9 min read··9 min read
Prompt to portfolio: how AI turns plain English into an investable index
From a sentence to a 40-stock basket with a documented selection rule, transparent weights, and a 25-year backtest — in thirty seconds. Here's how Arithmos's agent parses a prompt, picks a universe, and writes the rule so you can actually read it.
productAIhow-it-works - Index strategy · deep dive··11 min read
Best alternatives to the S&P 500 in 2026
The S&P 500 is not the only game in town. Here's a data-driven tour of eight credible alternatives — equal-weight, quality-factor, global, and custom — with returns, volatility, and when each actually makes sense.
strategybenchmarksfactors - Tutorial · 11-step playbook··14 min read
How to build your own index fund (without a $10m minimum)
A step-by-step guide to constructing a rules-based index — picking a universe, choosing weights, setting a rebalance cadence, back-testing, and actually buying it at your broker. The way institutional investors have done it for forty years, now for retail.
tutorialportfolio-constructionbacktesting - Performance · 1Y / 5Y / 10Y··9 min read
Top index fund performance: a long-horizon leaderboard
A clean, annually-reviewed ranking of the best-performing index funds across every meaningful slice — broad market, factor, sector, country, thematic — and how to read the numbers without getting fooled.
performanceETFsleaderboard
Every concept on this blog (weighting, backtesting, factor exposure, attribution) is a button on the product. Describe the exposure you want, the agent picks the names and weights, and you can export the result to any broker.
