Stock average calculator

Combine an existing holding with an additional purchase.

On your device · No account

Privacy details

Stock average calculator processes your input in this browser. Inputs and results are excluded from analytics. Recent tools save tool names, visit counts and last-visit times. Saved tools store only their names. Draft saving is optional and stays on this device; delete saved text with the draft controls. Loading text from a URL is optional and contacts that server; its URL and your IP address are visible to the server. An optional “Use in” action keeps a handoff in this tab. The next tool removes it on arrival and ignores it if more than a minute has passed.

Copy link includes the inputs you choose to share in the address. Anyone with that link can reopen them. Files and generated results are excluded. Password and key tools share settings only.

Existing shares

Existing average cost per share

More inputs and assumptions

Additional shares

Additional cost per share

Answer

…

Average cost = total purchase cost ÷ total shares. Sum the existing and new positions before dividing.

More results

Precision and calculation record

Decimal places in numeric results and text downloads

Rounding changes displayed numbers, not the calculation. Text, fractions, matrices and CSV schedules keep their own formatting. Automatic keeps up to 12 significant digits, with money shown to cents where applicable.

Saved scenario

Save the current answer, then change an input to compare. This clears when you leave.

Formula and assumptions

Use the same security and currency. Include fees in the entered costs if appropriate. This is a weighted average, not a tax-lot basis calculation or investment recommendation.

Automatic precision shows money to two decimal places and other numbers to 12 significant digits. Thousands separators such as 1,000 are accepted; use a dot for decimals.

Scratch calculator

Check another calculation

Use +, −, ×, ÷, parentheses and %. A percentage is divided by 100. This does not change the main tool.

Reset reloads the tool with its starting values and releases open files and device controls. Saved drafts stay on this device until you delete them.

Links include your inputs and settings. Anyone with the link can see them, so leave out private text. Files and generated results are left out; random draws run again.

Keyboard shortcuts

Updated 2026-09-26

Using Stock average calculator

Average cost = total purchase cost ÷ total shares. Sum the existing and new positions before dividing.

Use the same security and currency. Include fees in the entered costs if appropriate. This is a weighted average, not a tax-lot basis calculation or investment recommendation.

Next: Return on equity calculator

A worked example

With existing shares = 10, existing average cost per share = 20, additional shares = 5, additional cost per share = 26, the new average cost is 22.

Next: Stock profit calculator

Before you use the result

Use the same security and currency. Include fees in the entered costs if appropriate. This is a weighted average, not a tax-lot basis calculation or investment recommendation. Calculations keep full browser-number precision. Money amounts are displayed to two decimal places; other results use up to 12 significant digits. Very large values may lose precision.

Example results for existing shares

These examples use Existing average cost per share: 20; Additional shares: 5; Additional cost per share: 26. They are reference calculations, not recommended settings.

Existing shares	New average cost
5	23
10	22
20	21.2

Cite this page

Citation style

ToolOctopus. “Stock average calculator.” Updated 2026-09-26. https://tooloctopus.com/stock-average-calculator.

Add an access date if your instructions require one.

Citation formatting uses citeproc-js by Frank Bennett and Citation Style Language styles. Licence and source code.