There is no single "correct" platform. Different brokers win different segments — and some are stronger in the US, others in Europe, others in emerging markets. Here's a short, factual map.
| Region | Largest commission-free / low-cost | Largest full-service |
|---|---|---|
| United States | Robinhood, Fidelity, Schwab, M1, SoFi | Fidelity, Charles Schwab, Vanguard |
| United Kingdom | Trading 212, Freetrade, Lightyear | Hargreaves Lansdown, AJ Bell, Interactive Investor |
| Continental Europe | Trade Republic, Scalable Capital, BUX, Degiro | Comdirect, BNP Paribas, ING |
| Asia-Pacific | Tiger Brokers, Futu (Moomoo), CMC Markets | Saxo, Interactive Brokers |
| Global / multi-asset | Interactive Brokers, eToro, Saxo | Interactive Brokers Pro |
Where Arithmos fits
Arithmos is broker-agnostic. The index you build can be exported as CSV, as a Trading 212 Pie, or as a Fidelity Basket. The CSV imports cleanly into Schwab, Vanguard, Hargreaves, AJ Bell, Interactive Brokers, eToro and most other platforms.
FAQ
What's the cheapest way to hold a 50-stock custom index?
In the UK, a Trading 212 Pie holds up to 50 names commission-free with fractional shares. In the US, Fidelity Stocks-by-the-Slice and Schwab Slices both support fractional baskets. Outside the EU/UK, Interactive Brokers' fractional shares plus a basket order is the most common pattern.
Can I auto-rebalance my Arithmos index?
Trading 212 Pies auto-rebalance on contribution. The Plus and Pro Arithmos plans will support email alerts when an index drifts beyond a configurable band — automated rebalancing requires broker-side APIs we're integrating selectively.
