Trading 212 Pies are one of the cleanest fractional-share products on the market. You set the holdings, set the weights, and Trading 212 handles the rebalancing in fractional units. The only painful part is the bit before that, deciding what should be in the Pie in the first place.
Arithmos closes that gap. Describe the exposure you want in a sentence, the agent picks the names, sets the weights, runs the backtest, and exports the Pie file. You import it, fund it, and Trading 212 takes it from there.
The flow
- Type the index you want into the prompt box. Example: "FTSE 250 quality compounders, equal-weighted, no banks, capped at 6% per name."
- Arithmos returns the holdings, the weights, and a backtest with CAGR, vol, Sharpe, and max drawdown.
- Click export, pick Trading 212 Pie. You get a JSON file the importer reads.
- Open Trading 212, create a Pie, import the file. Holdings and weights land in the Pie ready to fund.
- Set your direct-debit or one-off deposit. Trading 212 buys the fractional shares to match the Pie weights.
What you get that the standard Pie builder does not
- A 20+ year backtest before you commit a single pound.
- An explicit, auditable rule for why each name is in. Not a vibe, a screen.
- Easy exclusions, ex-tobacco, ex-mining, ex-Magnificent-Seven, ex-China-A-shares.
- A weighting scheme beyond cap or equal, free-cash-flow yield, risk-parity, inverse-volatility.
- An update flow when the screen changes, the agent re-runs and you re-import, no spreadsheet work.
Worked example, a Trading 212 user could ask for
FTSE 100 ex-tobacco ex-mining, equal-weighted, capped at 5% per name, rebalanced quarterly.
The agent removes BAT and Imperial Brands from the tobacco screen, removes the four FTSE 100 miners, equal-weights the remaining roughly 80 constituents, applies the 5% cap (which does not bind on equal weight), and runs a 10-year backtest. Export to Pie, import, fund.
Fees, the boring but important bit
Arithmos charges the subscription, Trading 212 charges what they always charge. There is no spread, no commission, no broker fee added by us, you trade at Trading 212's quoted prices using their FX. We are the layer in front of the broker, not a new broker.
FAQ
Does the Arithmos export actually load into Trading 212?
Yes. Arithmos generates the Pie JSON in the format the Trading 212 importer reads. Open the app, create a new Pie, paste the file in, and the holdings and weights come across. We do not place orders for you, Trading 212 does that when you fund the Pie.
Does this work inside a Stocks and Shares ISA?
Yes. The Pie sits in whatever account you choose at Trading 212. If your Pie lives in your ISA, the dividends and capital gains stay inside the ISA wrapper. Arithmos does not touch your account permissions, it just builds the basket.
What if Trading 212 does not list a stock the index needs?
We flag it during build. Most large-cap names are listed at Trading 212, but small-cap and some EM names are not. You can either drop those names or pick a similar replacement, the agent does both and shows you the impact on the backtest.
