How do I calculate my average cost per share?

Divide the total amount spent by the total number of shares. Add up (shares x price) for every purchase, then divide by the sum of the shares — not by the number of purchases.

What is averaging down?

Buying more of a holding at a lower price than you paid, which reduces your blended cost per share. It lowers your break-even price but also increases the amount committed to a position that has fallen.

Does my broker calculate this the same way?

Brokers generally report an average cost, but tax reporting may use specific-lot identification instead, which can produce a different gain or loss. Your broker’s records are the ones that count at tax time.

Stock Average Calculator

Combine every purchase of the same stock into one blended average cost per share, and see the unrealized profit or loss at any current price.

SharesPrice per share

Average cost per share: $132.00
Total shares: 25
Total cost: $3,300.00

Current price (optional)$

How this is calculated

average cost = sum(shares x price) / sum(shares)

shares x price: the amount spent on one purchase
sum(shares): every share held, not the number of purchases

Worked example

Buying 10 shares at $150 ($1,500) and 15 at $120 ($1,800) is $3,300 across 25 shares, so the average cost is $132.00 — not $135.00, which is what averaging the two prices would wrongly give.

Common questions

How do I calculate my average cost per share?: Divide the total amount spent by the total number of shares. Add up (shares x price) for every purchase, then divide by the sum of the shares — not by the number of purchases.
What is averaging down?: Buying more of a holding at a lower price than you paid, which reduces your blended cost per share. It lowers your break-even price but also increases the amount committed to a position that has fallen.
Does my broker calculate this the same way?: Brokers generally report an average cost, but tax reporting may use specific-lot identification instead, which can produce a different gain or loss. Your broker’s records are the ones that count at tax time.

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This tool performs arithmetic on the figures you enter. It is for informational and educational purposes only, is not investment, tax or financial advice, and is not a recommendation to buy, sell, or hold any security. Projections are assumptions, not forecasts. Always do your own due diligence.

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