Average Cost Calculator
Compute the quantity-weighted average price (cost basis) across multiple buys, plus total quantity and total cost — useful for understanding a scaled-in position.
Calculator
Each line is one fill: price, quantity.
Formula
- Average price = Σ(Price × Quantity) ÷ Σ Quantity
- Total cost = Σ(Price × Quantity)
How it works
When you build a position in several fills at different prices, your effective entry is the quantity-weighted average of those prices — not a simple average. This calculator computes that blended cost basis along with total quantity and total cost.
Knowing your average is the basis for measuring break-even and unrealized profit or loss. Adding to a position at a lower price lowers the average, but it also increases your total exposure and the capital at risk — a fact this tool makes explicit without suggesting whether to do it.
This is arithmetic on the fills you enter. It is not advice about whether, when, or how much to add to any position.
Example use cases
Two equal lots
10 units at $100 and 10 units at $90 → average $95 on 20 units, total cost $1,900.
Quantity-weighted
1 unit at $100 and 9 units at $50 → average $55 (weighted toward the larger lot).
Frequently asked questions
Does averaging down reduce my risk?+
No — that is a common misconception. Lowering your average price also increases the size of the position and the total capital exposed, so it raises absolute risk even as it lowers the break-even price. This tool computes the average; it does not recommend the action.
Should I include fees in the price?+
For a more accurate cost basis, fold per-fill commissions into the effective price of each fill. See the Brokerage Calculator to estimate those costs.