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How can I calculate total return of stock with partial sale?
Treat each position or partial position as a separate LOT. Each time you open a position, a new lot of shares is created. If you sell the whole position, then the lot is closed. Done. But if you sell a partial quantity, you need to create a new lot. Split the original lot into two. The quantities in each are the amount sold, and the amount remaining. If you were to then buy a few more shares, create a third lot. If you then sell the entire position, you'll be closing out all the remaining lots. This allows you to track each buy/sell pairing. For each lot, simply calculate return based on cost and proceeds. You can't derive an annualized number for ALL the lots as a group, because there's no common timeframe that they share. If you wish to calculate your return over time on the whole series of trades, consider using TWIRR. It treats these positions, plus the cash they represent, as a whole portfolio. See my post in this thread: How can I calculate a "running" return using XIRR in a spreadsheet?