Simulate stock or ETF purchases and replacements with portfolio impact analysis

Let investors try a stock or ETF purchase or switch against their own portfolio without recording a real trade. Start from a stock detail or research view, choose a portfolio and amount, and say whether the purchase uses existing cash, a new contribution, or proceeds from selling an existing stock or ETF. Support a partial or full sale of one holding. A purchase of a stock already held should increase that hypothetical position, and unused sale proceeds should remain as cash. Show sale proceeds, purchase cost, assumed prices, currency conversion, fees and remaining cash. Do not allow a sale larger than the holding or a purchase that exceeds its funding source.

Compare the current and proposed portfolio side by side: position weights, largest holdings, sector and geographic allocation, and cash. Show both monetary and percentage changes with clear denominators, especially when new capital is added. Where sufficient history exists, compare volatility, beta, Sharpe ratio, drawdown, risk contributions and relevant scenarios on a consistent historical basis. A larger portfolio should not be labelled riskier solely because its monetary value grew. Show when an asset lacks enough history for a metric rather than treating missing data as zero risk. For a sale, show supported estimates of realized gains and tax separately from available trading cash. Do not present an unavailable tax estimate as zero.

The existing AI Assistant already handles some hypothetical purchase and replacement questions, including allocation and supported fund comparisons. This request would make the decision easier to explore from stock research and portfolio pages, with a clear before-and-after view. Related research ideas include multiple named watchlists with saved, sortable views; regular-session and pre-market or after-hours movers labelled with their reference prices and timestamps; and analyst ratings, target ranges and revisions where reliable data is available. Those are ideas to assess separately from the purchase and switch flow.

The initial purchase and switch flow covers one stock or ETF purchase funded by cash, a contribution, or one stock or ETF sale. It does not place orders or model multi-trade baskets, short sales, bond or option replacements. Historical comparisons describe past data, not an expected future outcome.