Investing
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
-
Total shares
-
Total invested
-
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.
Frequently Asked Questions
Not necessarily. A lower average cost can also mean more capital is concentrated in the same position.
For exact brokerage reconciliation, include commissions and fees in total invested amount.
Yes. Enter fractional share quantities if your broker supports them.