Stock Average Cost Calculator
Calculate your new average share cost after an additional stock purchase, including total shares and total invested amount.
What does this calculator answer?
Average stock cost is total invested amount divided by total shares owned. After buying more shares, the key number is the new average cost and how much additional capital you have committed.
Inputs
Results
New average cost
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Total shares
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Total invested
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Before you enter values
- Enter current shares in shares so the estimate uses the same unit throughout.
- Enter current average cost in USD so the estimate uses the same unit throughout.
- Enter new shares bought in shares so the estimate uses the same unit throughout.
- Enter new purchase price in USD so the estimate uses the same unit throughout.
How to read the result
- Start with 'New average cost'. This is the main output for the current assumptions.
- Then compare 'Total shares' so you do not judge the scenario from one number alone.
- Then compare 'Total invested' so you do not judge the scenario from one number alone.
Formula
New average cost = (current shares × current cost + new shares × new price) ÷ total shares
Example
If you own 20 shares at $50 and buy 10 more at $40, your total invested amount is $1,400, total shares are 30, and the new average cost is about $46.67.
Common mistakes
- Confusing current market price with average cost
- Ignoring trading fees when reconciling brokerage records
- Focusing only on a lower average cost while total exposure rises
Important note
This calculator only models user-provided numbers. It does not provide investment advice or a buy/sell recommendation.
Review and update policy
This page was reviewed on August 6, 2026 for formula wording, default inputs, FAQ coverage, and related calculator links. Investing and AI cost calculators do not pull live market prices or account-specific pricing, so you should enter the latest values yourself.
When official sources are relevant, source links are provided on the page. If a formula, rate, or source is outdated, send the page URL and supporting reference through the contact page.