How the Stock Average Cost calculation works

Your average cost per share is simply your total money spent on shares divided by the total number of shares you own (from the purchases you entered). The only “trick” is making sure you’re adding each buy correctly — and deciding whether to include fees.

If you bought n lots, and each lot i has shares sᵢ, then:
Total shares = s₁ + s₂ + … + sₙ.

Each lot has a buy price pᵢ and an optional fee fᵢ (commission, brokerage fee, taxes/charges you want to treat as part of cost). The cost of one lot is:
Lot cost = (sᵢ × pᵢ) + fᵢ.
Add all lots to get:
Total cost = Σ[(sᵢ × pᵢ) + fᵢ].

Finally:
Average cost per share = Total cost ÷ Total shares.
This number is also your basic break-even price (before taxes and after accounting for fees you included). If the market price is above this, you’re in unrealized profit; if below, unrealized loss.

If you enter a current price P, the calculator estimates:
Unrealized P/L = (P − Average cost) × Total shares.
The tool also shows a percent change relative to your total cost:
P/L % = Unrealized P/L ÷ Total cost × 100.

If you set a target profit amount T (like “I want to be up $500”), the required price becomes:
Target price = Average cost + (T ÷ Total shares).
This is a clean “goal line” for screenshots — but it’s not a guarantee the market will reach it.

Example: averaging down (and why fees matter)

Imagine you bought the same stock three times:

• Buy 1: 10 shares at $50, fee $0 → cost = 10×50 = $500
• Buy 2: 10 shares at $40, fee $0 → cost = 10×40 = $400
• Buy 3: 20 shares at $35, fee $0 → cost = 20×35 = $700

Total shares = 10 + 10 + 20 = 40. Total cost = 500 + 400 + 700 = $1,600. Average cost = 1,600 ÷ 40 = $40.00/share.

Now suppose today’s price is $42.50. Unrealized profit = (42.50 − 40.00) × 40 = $100. That’s a 100 ÷ 1,600 = 6.25% unrealized gain.

If your broker charged a $5 fee on each buy, total fees are $15. Total cost becomes $1,615, so average cost becomes 1,615 ÷ 40 = $40.375/share. Small difference — but it’s the more accurate break-even if fees were real cash outflows.

In the example, the first purchase was at $50. After adding buys at lower prices, the break-even dropped to ~$40 (or $40.38 with fees). That can make recovery easier — but it also means you’ve invested more total cash. The calculator helps you see both sides clearly: average cost goes down, but total exposure goes up.

Step-by-step: get your average cost in 30 seconds

• Add each buy: enter shares, buy price, and optional fees. Use “Add buy” for more rows.
• (Optional) Add current price: see your unrealized profit/loss instantly.
• (Optional) Add target profit: get the price needed to reach that profit.
• Calculate: the result box shows total shares, total cost, average cost, break-even, and P/L.
• Copy/Share: perfect for “here’s my break-even” screenshots and quick chats.

• Mistake: averaging prices instead of averaging by shares. Fix: This tool weights by shares automatically.
• Mistake: forgetting fees. Fix: Add fees per buy (or leave at zero).
• Mistake: mixing buys and sells. Fix: This calculator is for buys only; sells change your cost basis method (FIFO/LIFO/average cost varies by country/broker).

If you need to include sells, dividends, splits, or taxes, use your broker’s cost basis report (or a full portfolio tracker). This tool is designed for quick, practical average-cost snapshots.

Frequently Asked Questions

• Is “average cost” the same as “break-even”?

  For a simple buy-only position, yes: your average cost per share is your basic break-even price. If you included fees, the break-even includes those fees too. Taxes and spreads may still affect your real break-even.

• Why can’t I just average my buy prices?

  Because the number of shares matters. Buying 1 share at $100 and 100 shares at $10 doesn’t average to $55 — it’s much closer to $10 because most of your shares were bought there. This calculator uses a weighted average: total cost divided by total shares.

• What about stock splits?

  After a split, your share count changes and your per-share cost changes, but your total cost stays the same. Easiest approach: enter your post-split share counts and post-split buy prices, or use your broker’s adjusted figures.

• Does this work for crypto or ETFs?

  Yes. The math is identical for any asset where you buy units at different prices (stocks, ETFs, crypto, even commodities). Just enter “shares” as “units”.

• Does averaging down always make sense?

  Not always. Averaging down lowers break-even, but increases exposure. Many investors use it with a plan (DCA schedule, risk limits, diversification). This tool helps you see the math clearly; the decision is up to you.

• Can this replace my broker statement?

  No. Use your broker for official cost basis (especially for taxes). This tool is for quick planning, learning, and shareable snapshots.