Stock Average Calculator
Buying 10 shares at $50 and 15 shares at $42 gives you a $45.20 average cost per share. This stock average calculator combines at least two share purchases into one weighted average cost per share. It also shows your total shares and total cost basis so you can track how later buys change your average entry price.
Quick answer
Each purchase affects the average based on how many shares you bought at that price.
Purchase 1
Purchase 2
This estimate combines purchase lots only. It does not adjust for fees, taxes, stock splits, wash sales, or partial sales.
What this tells you
- •Each purchase affects the average based on how many shares you bought at that price.
- •A larger purchase pulls the average more than a smaller purchase does.
- •The result is your weighted average cost per share before fees, taxes, and broker adjustments unless you already built those into your lot prices.
How to Use
- 1Enter the share count and price per share for your first purchase.
- 2Add your second purchase, then include any extra lots you want to combine.
- 3Calculate to see the weighted average cost per share across all completed lots.
- 4Use the total shares and total cost basis to compare your average entry price with the current market price.
How It Works
Formula
Total cost basis = Σ(shares × price per share)
Total shares = Σ(shares)
Average cost per share = total cost basis ÷ total sharesThis calculator uses a weighted average. Each lot contributes its own cost basis, found by multiplying shares by price per share. After adding all lot costs and all share counts, the combined cost basis is divided by the combined shares to get one average cost per share.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
Average down after a lower-price buy
The total cost basis is $500 + $630 = $1,130. Divide $1,130 by 25 shares to get a weighted average cost of $45.20 per share.
Three-lot dollar-cost averaging example
These three lots add up to $2,625 of cost basis across 25 shares. Dividing $2,625 by 25 gives you a $105 average cost per share.
How the weighted stock average works
The average moves toward the lots with more shares.
| Purchase | Shares | Price per share | Lot cost |
|---|---|---|---|
| Lot 1 | 10 | $50 | $500 |
| Lot 2 | 15 | $42 | $630 |
| Combined | 25 | $45.20 average | $1,130 |
The combined row is not a simple midpoint between $50 and $42. It is weighted by the share count in each purchase.
Common mistakes
- Using a simple midpoint between prices instead of weighting each lot by share count
- Leaving out fees or commissions when you want a true adjusted cost basis
- Mixing buys, sells, stock splits, or wash sale adjustments into one average without checking broker records
Limitations
This stock average calculator combines buy lots only. It does not adjust for commissions, fees, taxes, dividend reinvestment bookkeeping, stock splits, wash sales, or partial sales. Broker statements and tax records can use more detailed adjusted cost basis rules than this simplified weighted-average estimate.