Average Cost Calculator

How to use this calculator

1. Enter the Purchase 1 price and Purchase 1 quantity, then fill in purchases 2 to 4 if you have them. Leave unused rows at 0.
2. Enter the Current price per unit.
3. Read the Average cost per unit, then check total cost, current value, profit or loss and return.

How average cost works

The average cost is a weighted average: each purchase counts in proportion to how many units you bought. Buying 100 units at $50 and 150 at $42 does not average to $46, because you bought more at the lower price.

average cost = (P₁Q₁ + P₂Q₂ + … ) / (Q₁ + Q₂ + …)

• Pᵢ = price paid per unit in purchase i
• Qᵢ = number of units bought in purchase i
• profit or loss = current price × total units − total cost

Add up what you paid in total and divide by the number of units. Rows with a zero price or quantity are ignored.

Example: two purchases

You buy 100 shares at $50 and 150 shares at $42. Total cost is $11,300 for 250 shares, so the average cost is $45.20, not the simple midpoint of $46.

At a current price of $46 the position is worth $11,500, a profit of $200 or 1.77%. Add a third purchase of 100 shares at $38 and the average falls to $43.14, total cost becomes $15,100 and the profit at $46 rises to $1,000, or 6.62%.

Averaging down and dollar-cost averaging

Buying more after a price drop lowers your average cost, and your break-even price falls with it. That does not make the investment better; it only changes your starting point. Buying more of a falling asset also concentrates your risk, so decide first whether you would buy it at today's price.

Investing a fixed amount at regular intervals, known as dollar-cost averaging, automatically buys more units when prices are low. To value the whole position, see the stock profit calculator and the ROI calculator.

How to use the result

Your average cost is your break-even price before fees. If the current price is below it, selling realizes a loss; above it, a gain. Compare the return with what you could expect elsewhere and think about taxes, since many countries use specific rules for matching purchases with sales.

A practical habit is to record each purchase date, price, quantity and fee in one place. Then rerun the calculator whenever you add a lot, and compare the average cost with the current price before deciding to add more, hold or sell. If you plan to sell only part of a position, remember that the cost of the units sold may be calculated differently from the simple average, so check which method your broker and tax authority apply.

Common mistakes

• Averaging the prices without weighting by quantity.
• Forgetting fees and commissions, which raise your real cost per unit.
• Ignoring reinvested dividends, which are extra purchases at their own prices.
• Assuming the tax authority uses the same average method as your broker.

Assumptions and limits

The calculator handles up to four purchases and does not include commissions, dividends, splits or currency conversion. It reports an unrealized result at the price you enter. For tax filings use your broker's cost-basis statement.

Frequently asked questions