How to use the stock average calculator
- Add each purchase: the number of shares and the price paid. Add a row for every buy.
- Add the fee per purchase if your broker charges one. It is included in the cost.
- Enter the current price to see the value and your gain or loss.
- Plan your next buy. Enter the average you want and the price you could buy at, and the calculator tells you how many shares it takes.
The formula
It is a weighted average: a buy of 100 shares moves the average far more than a buy of 5. To reach a target average T by buying at price P, you need (total cost − T × shares) ÷ (T − P) more shares.
Example
You bought 20 shares at 48.50, 15 at 41.20 and 10 at 37.80: 45 shares for 1,966. Your average is 43.69. At today's price of 40 you are down 166, or 8.4 %. To bring the average down to 40 by buying at 36, you would need about 41.5 more shares, costing roughly 1,495.
Before you average down
- Ask why the price fell. A lower average does not help if the business is getting worse.
- Keep any single share to a sensible part of your portfolio.
- Averaging into a broad index fund over time is far less risky than averaging into one company.
Frequently asked questions
Do sales change my average?
Selling some shares does not change the average cost of the shares you keep under the average-cost method. Tax rules for working out gains differ by country.
Should fees be included?
Yes. Fees are part of what each share really cost you, and many tax systems include them in the cost basis.
Weighted average cost method. Illustrations only, not advice.
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Last reviewed: 2026-11-08. Results are estimates based on the returns you enter, not advice. See our disclaimer.