How to use this share average calculator
Find your average share purchase price after multiple purchases. Enter the price and share count for each lot, using a single currency throughout. Results include total shares, total purchase amount, and the share-count-weighted price, with a breakdown for checking your entries.
- Enter the share price 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.
Share Average formula
Average share price = total purchase amount ÷ total shares
A later purchase below the existing average lowers the combined purchase price. A purchase above it raises the average. The number of new shares determines the size of that change; this arithmetic does not predict future returns.
Follow the numbers
100 shares at 50 and 50 shares at 40 cost 7,000. The average share price is 7,000 ÷ 150 = 46.666667.
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
Keep different securities separate. Fees, sales, and tax-lot rules are outside this purchase-only calculation.
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. Keep different securities separate. Fees, sales, and tax-lot rules are outside this purchase-only calculation.
Frequently asked questions
What formula does this calculator use?
Average share price = total purchase amount ÷ total shares. 100 shares at 50 and 50 shares at 40 cost 7,000. The average share price is 7,000 ÷ 150 = 46.666667.
What should I check about the method?
Keep different securities separate. Fees, sales, and tax-lot rules are outside this purchase-only calculation.
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.