AlgovestIQCost basis math
Enter the shares and price of each purchase to get your true average cost per share, your break-even price with fees, and your gain or loss at today's price. Planning to average down? Switch to target mode to see how many shares at a new price bring your average to the level you want.
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Each bar is one purchase. The average weights each by its share count.
Averaging down means buying more of a stock below your current average so your cost per share falls. To find how many shares that takes, choose the average you want and the price you expect to pay:
New shares = shares held x (current average - target average) / (target average - new price)
If you hold 50 shares at a $120 average and can buy at $90, reaching a $105 average takes 50 more shares, which cost $4,500 before fees. The target has to sit between your current average and the new price: a purchase at $90 can never pull the average to $90 or below. The same formula works for averaging up when the new price is above your average.
Fees are kept out of the average price. They add to the cash the purchase needs and raise your break-even price, which the calculator shows separately. A lower average does not make a falling stock a better investment; it also puts more money into the same position.
When you buy the same stock more than once, your cost per share is a weighted average: each purchase counts in proportion to the number of shares it added. Fees do not change what you paid per share, but they do raise the price you need to sell at to break even.
Average price = sum(shares x price) / total shares
Total invested = sum(shares x price) + fees
Break-even price = total invested / total shares
Shares to reach a target average = existing shares x (current average - target) / (target - new price)
You buy 10 shares at $100 and later 30 shares at $80, paying a $5 fee each time. Your purchases cost $3,400 for 40 shares, an average price of $85.
With $10 of fees you have invested $3,410, so your break-even price is $85.25. At a current price of $90 the position is worth $3,600, a gain of $190 or about 5.6%.
Averaging down to a target: you hold 50 shares at a $120 average and the stock now trades at $90. To bring your average to $105 you need 50 x (120 - 105) / (105 - 90) = 50 more shares, costing $4,500 before fees. A target at or below $90, or above $120, cannot be reached by buying at $90.
Related tools are selected for the stock average price calculator workflow.
Measure a sale with fees, percentage return and annualized return.
Calculate profitDecide how many more shares fit your risk before averaging down.
Size the next positionSee what buying on a schedule would have averaged out to.
Backtest regular investingMultiply each purchase's shares by its price, add those amounts together, and divide by the total number of shares. 10 shares at $100 and 30 shares at $80 cost $3,400 for 40 shares, an average of $85.
Larger purchases count for more. The simple average of $100 and $80 is $90, but if you bought three times as many shares at $80, your true average cost is $85.
The average price shows what you paid per share before fees. Fees are added to total invested and to the break-even price, which is the price at which selling would recover every dollar you put in.
Multiply your current shares by the gap between your current average and the target, then divide by the gap between the target and the new purchase price. 50 shares at $120, buying at $90 to reach $105, needs 50 x 15 / 15 = 50 shares. The target must sit between the new price and your current average.
Yes. Buying more shares below your current average lowers the average and the break-even price, but it also increases how much you have invested in the position.