Stock Average Cost Calculator
Calculate your average cost per share and simulate averaging down
Enter the price and share count for each of your purchases and this calculator works out your total cost basis, total shares held, and average cost per share. Set a target average and a price you'd buy at, and it also tells you exactly how many more shares you'd need to buy to hit that target. Every calculation runs in your browser, so your trade details never leave your device.
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🔒 Everything runs 100% in your browser. Your files and input are never uploaded to any server.
How to use
- Enter your purchase history one row at a time with the price paid and number of shares (use "+ Add purchase" for more rows).
- Your total cost, total shares, and average cost per share are calculated and displayed automatically.
- Planning to average down? Enter your target average cost and the price you expect to buy at.
- The tool calculates the extra shares and cash required, and the copy button exports the whole breakdown as text.
FAQ
- How does the averaging-down calculation work?
- It takes your current share count, current average cost, target average, and planned purchase price, then solves backward for the number of additional shares needed to reach that target. Your purchase price has to be below the target average for the average to come down at all.
- Why do I get an error saying the target average is unreachable?
- If the math produces a negative result — say your target is far below your current average, or your purchase price equals or exceeds the target average — the target can't be reached, so an error message is shown instead.
- Is my trade data saved?
- No. Everything is calculated inside your browser with no storage and no transmission to a server, so refreshing the page clears your entries.