Enter all four values above zero to see your new average.
- Total shares
- Total invested
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- Additional cash needed
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Must be between the current price and your average cost.
Enter all four values above zero to see how many shares to buy.
- Cost of purchase
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- Total shares after
- Total invested after
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- Resulting average cost
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Assumes fractional shares are allowed. If your broker only trades whole shares, round up to stay at or below the target.
Rows missing a value are ignored in the average.
Enter shares and price for at least one lot to see the weighted average.
- Total shares
- Total cost
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How it works
Your average cost per share is your total money in divided by your total shares. Buying more shares below your current average pulls the average down toward the new buy price — it can never go below it.
New average after a buy
S₀ = shares owned, A₀ = current average cost, S₁ = shares bought, P = buy price per share.
Shares needed to reach a target average
T = target average. Only possible when P < T < A₀: the target must sit between the current price and your existing average.
Weighted average across lots
Break-even after averaging down
Worked example
You own 100 shares at an average of 10.00 and buy 100 more at 5.00. Total invested is 100×10.00 + 100×5.00 = 1,500 across 200 shares, so the new average is 7.50 — a 25.00% reduction. From the 5.00 buy price, the stock must rise 50.00% to reach the new 7.50 break-even.
This tool only does the arithmetic — it is not investment advice. Averaging down increases your exposure to a falling position.