BasisPilot

There comes a point, after years of buying the same fund every month, when nobody can say what one share cost on average. The calculators on BasisPilot work that out in the browser, along with how large a trade may be when you accept only a set loss. Each result comes with the formula behind it and the assumptions it rests on.

The savings plan calculator splits a future total into money paid in and estimated growth. For traders, the position size calculator turns a risk limit and a stop price into a number of shares. Market prices are typed in by hand, and the cost calculator counts purchases only, which leaves sales and tax-lot rules out. The about page says inputs stay on your device unless you create a share link.

The site, in English and Chinese, also has research pages built from public US filings. A 13F tracker shows what 11 large investment firms reported holding each quarter, from SEC records that can arrive up to 45 days after the quarter ends. A scanner ranks about 100 US stocks by unusual trading activity after each market close, with a note that its scores say nothing about future returns.