Average Cost Calculator
Enter each purchase to get your average cost, or work backwards to find how much to buy to average down.
| # | Price paid | Quantity |
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How it works
Average cost = total amount spent / total shares. It is your break-even line: sell above it and you make money, sell below it and you lose. To average down, the calculator solves for how many shares at today's price bring your average to the target: shares to buy = held x (current average - target) / (target - current price).
Fees and sale taxes mean that selling exactly at your average cost still loses a little. Check your real result with the stock profit calculator, or use the percentage calculator for quick percentage changes.
Frequently asked questions
How do I calculate my average cost per share?
Add up what you paid for every purchase and divide by the total number of shares. If you bought 10 shares at 100 and 10 shares at 80, your average cost is (1,000 + 800) / 20 = 90. Simply averaging the two prices only works when the quantities are equal.
How many shares do I need to buy to average down?
Open the "Average down" tab and enter your current average cost, shares held, the current price and the average you want. The target must be above the current price and below your current average. The closer the target is to the current price, the more money it takes.
Is averaging down a good strategy?
It lowers your break-even price, but it also puts more money into a position that is falling, which can make losses bigger. Check that the reasons you bought still hold, and set a maximum amount for any single position in advance. This calculator is a maths tool, not investment advice.
Does it work for crypto and fractional shares?
Yes. Prices and quantities accept decimals, so you can use it for crypto, ETFs, funds or fractional shares.