Average Down & Cost Basis Calculator
Bought a stock at more than one price? Enter every buy to see your true blended average cost, total cost and share count — then add today's price for instant unrealized profit or loss. Works for any market and currency.
Your cost basis
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How the average is calculated
- Add a row for each purchase with its price and quantity — add or remove rows as needed.
- Total shares = the sum of every quantity you own.
- Total cost = the sum of each price × its quantity.
- Average cost = total cost ÷ total shares — the blended price you effectively paid.
- Optionally enter a current price to see position value, unrealized profit or loss, and percentage return.
A quick example
You buy 100 shares at $50 ($5,000), then the price drops and you buy another 100 shares at $40 ($4,000). You now own 200 shares for a total cost of $9,000, so your average cost is $9,000 ÷ 200 = $45 per share — down from your first buy of $50. If the price is now $48, your position is worth $48 × 200 = $9,600, an unrealized gain of +$600 (+6.67%).
The visual plots each buy on a price scale against your blended average so you can see how new purchases pull the average toward them. Buying below your average pulls it down; buying above pulls it up. This is a math tool to keep your records honest — not a suggestion to add to any position.
Frequently asked questions
How do you calculate average cost when you buy more shares?
Add up the total money spent across every purchase (each price × its quantity), then divide by the total number of shares you own. That weighted figure is your average cost per share. Example: 100 shares at $50 ($5,000) plus 100 shares at $40 ($4,000) is $9,000 for 200 shares, so your average cost is $45.
What is cost basis and why does it matter?
Cost basis is the total amount you've paid for a position, and the average cost per share is that total divided by your shares. It sets your breakeven price and is what most tax systems use to calculate a capital gain or loss when you sell. Knowing it precisely keeps your profit-and-loss and tax records accurate.
Does averaging down reduce my risk?
It lowers your average cost per share, which lowers the price you need to reach breakeven — but it also increases the money committed to a position that has already fallen. It changes your cost basis, not the quality of the investment. This tool shows the math clearly so you can make that decision with a full picture, not on emotion. It is not advice to average down.
How is unrealized profit or loss calculated?
Enter a current price and the calculator multiplies it by your total shares to get position value, then subtracts your total cost to get unrealized profit or loss. Dividing that by total cost gives your percentage return. It's 'unrealized' because you only lock in the gain or loss when you actually sell.
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Educational tool only — not financial advice, and not a recommendation to buy, sell or average any position. Investing involves substantial risk of loss. See more free tools.