Stock Average Calculator
Enter every purchase of a stock, ETF or coin to get your average cost per share, total invested and profit or loss at today's price. The average down planner then tells you how many more shares to buy to reach the average you want.
Optional: for profit / loss.
How to use the Stock Average Calculator
- List your buys, one per line: number of shares and price paid, for example
50, 120. Add a third number for fees if you want them in your cost basis. - Enter the current price to see your profit or loss and break-even.
- Plan the next buy: enter your target average and the price you expect to buy at.
- Read the results: average cost, shares needed to reach the target and how much that purchase costs.
- Check the table to see how the average changed after each buy, and download it as CSV.
Average cost and average down formulas
Average cost per share = total amount paid ÷ total shares = (n₁ × p₁ + n₂ × p₂ + … + fees) ÷ (n₁ + n₂ + …). It is a weighted average: bigger purchases pull the average further toward their price.
Shares needed to reach a target average when buying at price B:
x = N × (A − T) ÷ (T − B)
where N is your current share count, A your current average, T the target average and B the price of the next buy. The target must lie between B and A: you can only average down with a buy price below the target, or average up with a buy price above it.
Example: you own 150 shares at an average of $46.67 ($7,000 total). The stock is now $35 and you want a $42 average. x = 150 × (46.67 − 42) ÷ (42 − 35) = 100 shares, costing $3,500. Check: ($7,000 + $3,500) ÷ 250 = $42.00.
How much each extra buy moves the average
Starting position: 100 shares at a $50 average ($5,000). New buys at $40:
| Extra shares at $40 | Extra cost | New average | Drop in average |
|---|---|---|---|
| 25 | $1,000 | $48.00 | −$2.00 |
| 50 | $2,000 | $46.67 | −$3.33 |
| 100 | $4,000 | $45.00 | −$5.00 |
| 200 | $8,000 | $43.33 | −$6.67 |
| 400 | $16,000 | $42.00 | −$8.00 |
Each doubling of the extra purchase lowers the average by less: the average can approach the new buy price but never reach it. Averaging down also raises the amount you have at risk in one position, so weigh it against your overall plan.
Frequently asked questions
How do I calculate my average stock price?
Add up what you paid for all purchases and divide by the total number of shares: average = (shares₁ × price₁ + shares₂ × price₂ + …) ÷ (shares₁ + shares₂ + …). For example, 100 shares at $50 and 50 shares at $40 cost $7,000 for 150 shares, an average of $46.67.
How many shares do I need to buy to average down?
Shares needed = current shares × (current average − target average) ÷ (target average − buy price). With 150 shares averaging $46.67 and a buy price of $35, reaching a $42 average needs 150 × 4.67 ÷ 7 = 100 shares, costing $3,500. The target must be between the buy price and your current average.
Should I include commissions in the average?
Including fees gives your true cost basis and the break-even price you need to reach. Add the fee as a third number on a buy line (shares, price, fee) and it is spread across those shares.
Is averaging down a good strategy?
It lowers your break-even price, but it also increases how much you have in a position that has been falling. It can make sense when your reasons for owning the investment still hold, and it is risky when the price is falling for a lasting reason. This calculator only does the math; it is not investment advice.
Does selling shares change my average cost?
Under the average cost method, selling shares does not change the average cost of the shares you keep; it only reduces the share count. Tax rules for cost basis differ by country and account type (for example FIFO or specific lot identification), so check your broker's statement for tax purposes.
Can I use this for crypto or fractional shares?
Yes. Shares and prices accept decimals, so 0.25 BTC at 60,000 or 3.5 shares at 182.40 work the same way.