Log each buy and sell as it happens. The tracker keeps an average-cost book per symbol, so selling part of a holding books a realised gain against what those shares actually cost you and leaves the rest of the position intact. Where this site already has a stored closing price for a ticker it fills the current price in for you; type over it any time.

Positions

Loading reference prices…

Trade blotter

Order does not matter — trades are always applied in date order before anything is calculated. Fees are added to a buy and taken off a sell.