Stock Average Calculator
Average down your cost basis across multiple stock purchases to find your true break-even price, total shares, and amount invested.
Frequently Asked Questions
How is the average price calculated?
It is a share-weighted average: total money invested divided by total shares. Larger lots move the average more than smaller ones, so it differs from a simple average of the prices.
Should I include brokerage fees?
For a true cost basis, add fees and charges to the invested amount. The average then reflects your real break-even price.
Is my data stored?
No. Everything is calculated in your browser and nothing is uploaded.
Understanding the Stock Average Calculator
A stock average calculator works out your blended average cost basis when you buy the same stock across several purchases at different prices. Enter each lot's share count and price to see your total shares, total amount invested, and weighted average price per share. It helps investors who add to a position or average down track their true break-even point. Results are estimates for record-keeping and education, not buy or sell advice; all math runs privately in your browser.
How it works
The tool sums the money spent across every buy and divides it by the total number of shares, giving a share-weighted average rather than a simple average of the prices. Each lot contributes in proportion to how many shares it holds, so a large purchase moves the average more than a small one. Your average cost is the price the stock must reach for you to break even before fees and taxes. If you include brokerage charges, add them to the invested total so the average reflects your real cost. Compare the average against the current market price to gauge unrealized gain or loss.
Worked example
You buy 10 shares at 100, then 20 more at 85 as the price falls. Amount invested = 10×100 + 20×85 = 1,000 + 1,700 = 2,700. Total shares = 30. Average cost = 2,700 / 30 = 90 per share. So your break-even is 90, not the simple midpoint of 92.50, because the cheaper lot was larger. If the price recovers above 90, the whole position is in profit before fees.
Tips & common mistakes
- Use a share-weighted average, not a plain average of prices; larger lots count more.
- Add brokerage, taxes, and fees to your invested total so the average reflects true cost basis.
- Averaging down lowers your break-even but increases your exposure to a falling stock.
- A lower average does not make a weak company a good investment; the business still matters.
- Keep this per stock; never blend cost basis across different tickers in one average.
Sources & methodology
- • U.S. Securities and Exchange Commission, Investor.gov — Cost basis and dollar-cost averaging (https://www.investor.gov)
- • Investopedia — Average Cost Basis Method (https://www.investopedia.com/terms/a/averagecostbasismethod.asp)
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Reviewed by the TopOpenTools editorial team · Last updated June 2026. These tools provide general estimates for educational purposes only and are not financial, tax, insurance, investment, or medical advice. Verify important decisions with a qualified professional.