How to use this stock average calculator
Calculate the quantity-weighted average purchase price of stock bought in multiple lots. Enter each purchase price and number of shares to see total shares, purchase cost, and average cost per share. The calculation uses your entries and does not retrieve market prices.
- Enter the purchase price per share values in the labeled fields, using consistent units.
- Load the example to inspect the expected format, then replace it with your own values.
- Select Calculate and check the result alongside its working. Reset starts a fresh calculation.
Stock Average formula
Average stock cost = Σ(price × shares) ÷ total shares
Buying a larger lot gives its price more influence over the average. This helps reconcile purchase records but does not show whether the position is profitable without additional information about sales, fees, and current value.
Follow the numbers
10 shares at 100 and 20 at 110 cost 3,200 in total. Average cost is 3,200 ÷ 30 = 106.666667 per share.
Load the example above to inspect the entries, then change one value and calculate again. The result follows your selected method. Display rounding changes how the answer is shown; it does not change the underlying observations or weights.
What to check before using the result
Purchases only, in one currency. Sales, taxes, fees, splits, and jurisdiction-specific cost-basis accounting are excluded.
Keep enough precision in the source values for your task. A result calculated from rounded summaries can only be as precise as those summaries. If a number was mistyped or an observation is missing, correct the inputs and calculate again before copying or exporting the answer.
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Common mistakes to avoid
- Confusing a blank with zero. A real zero is an observation. Missing information is not automatically zero.
- Mixing incompatible scales. Use consistent units, or normalize values before combining them.
- Rounding too early. Keep the original values and round at the result stage.
- Using the wrong weighting. Purchases only, in one currency. Sales, taxes, fees, splits, and jurisdiction-specific cost-basis accounting are excluded.
Frequently asked questions
What formula does this calculator use?
Average stock cost = Σ(price × shares) ÷ total shares. 10 shares at 100 and 20 at 110 cost 3,200 in total. Average cost is 3,200 ÷ 30 = 106.666667 per share.
What should I check about the method?
Purchases only, in one currency. Sales, taxes, fees, splits, and jurisdiction-specific cost-basis accounting are excluded.
How many entries can I use?
Paste up to 10,000 values, or use up to 100 individual rows when the chosen input method supports them. Numbers must be finite and no greater than 1 trillion in magnitude. Group and old-count inputs have additional whole-number requirements.
Are the displayed decimals exact?
The calculation uses standard floating-point numbers and compensated addition. Results are rounded only for display. Very small values use scientific notation so they do not silently appear as zero. Select the display precision you need, while respecting the accuracy of your original data.
Are my entries saved or sent anywhere?
The calculator performs its arithmetic in your browser. It does not automatically store entries or send them to a server. Copy, print, and CSV actions happen only when you choose them.
Read our calculation methodology for supported precision, validation, and assumptions.