Stock Average Cost Calculator
Add all your purchase lots to find your weighted average cost per share and total cost basis. Enter a current price to see your unrealized gain or loss.
All calculations happen in your browser. No data is sent anywhere.
Add a Purchase Lot
Summary
| Total lots | — |
|---|---|
| Total shares | — |
| Total cost basis | — |
| Average cost / share | — |
Unrealized Gain / Loss
Understanding Average Cost
How average cost is calculated
Your average cost per share is a weighted average across all your purchase lots. The formula is: Total Cost ÷ Total Shares. A lot where you bought more shares (or paid more per share) has more weight in the average. This gives a truer picture of your break-even price than a simple average of prices paid.
Averaging down vs. averaging up
Averaging down means buying more shares after the price has fallen, lowering your average cost so you need a smaller recovery to break even. Averaging up means adding shares as the price rises — you're paying more than your current average, but you're increasing exposure to a position already working in your favor. Both strategies change your average cost and total risk; this calculator lets you model either scenario before you trade.
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Open calculator →FAQ
What is average cost per share?
Average cost per share is the weighted average price you paid for all your shares across multiple buy lots. It equals your total cost divided by total shares held. For example, buying 10 shares at $10 and 10 shares at $20 gives an average cost of $15 per share ($300 ÷ 20 shares).
What does averaging down mean?
Averaging down means purchasing additional shares after the price has dropped below your original cost, pulling your average cost per share lower. The strategy reduces the price recovery needed to break even, but also increases your total exposure to the position. Use this calculator to model exactly how much your average changes before you buy.
How is cost basis calculated for taxes?
Cost basis is what you paid for the shares, which is subtracted from the sale price to determine your taxable gain or loss. The IRS allows several methods — FIFO, specific identification, and average cost. This calculator uses average cost: total cost ÷ total shares. Consult a tax professional for your specific reporting needs.
What is unrealized gain or loss?
An unrealized gain or loss is the paper profit or loss on shares you still hold. Because you haven't sold, no taxable event has occurred. It equals (current price − average cost) × total shares. Enter a current price in the Gain/Loss section to see your unrealized P&L instantly.