Average Cost Calculator
Calculate a new weighted average stock cost after an additional purchase.
Enter your values
Understand this calculation
This calculator blends your existing stock position with a new purchase to estimate the updated weighted average cost per share.
Formula
Worked example
Owning 10 shares at an average cost of $100 and buying 5 more at $80 lowers the weighted average cost to about $93.33, before any fees.
How to interpret the result
A lower average cost changes your cost basis but does not by itself improve the economics or risk of the investment.
Assumptions & limitations
The calculation uses the entered cost basis and does not account for taxes, wash-sale rules, foreign exchange or broker-specific accounting methods.
Practical context
When this calculator is useful
Use average cost when you have bought the same stock at more than one price and want to know the blended cost basis after an additional purchase. It can clarify how a new trade changes the economics of an existing position.
How investors commonly use it
Investors commonly use the blended average to track the price level above which an unrealized position begins to show a gain before taxes and future transaction costs. It is also useful for recordkeeping when purchases occur in several lots.
What this metric does not tell you
Average cost does not indicate whether buying more shares is sensible. It ignores valuation, business quality, portfolio concentration and future price risk; lowering the displayed cost basis is not the same as reducing investment risk.