Cost Basis & Stock Average Calculator
Calculate your stock cost basis across multiple buy orders. Enter each transaction to find your weighted average share price, break-even point, total investment, and average down result.
You buy 100 shares at $50, then 50 more shares at $40 when the price dips. Your average cost becomes $46.67 per share — not $45, because you own more shares at the higher price. If the stock recovers to $50, you profit on all 150 shares.
Enter your purchases
Add each transaction to calculate your averageResults
Your average price calculationEnter your stock purchases and click calculate to see your average price.
Averaging Down Strategy
Understanding cost averaging in the stock market
Why does average price matter?
Your average purchase price (cost basis) determines your break-even point, the price at which you neither profit nor lose before fees or taxes. Every time you buy more shares at a different price, your cost basis shifts. Knowing this number helps you understand the position accurately.
For example, if you buy 100 shares at $50 and later 200 shares at $35, your average drops to $40 per share. The stock only needs to recover to $40 for you to break even before fees and taxes, not back to $50. This is why tracking your true cost basis matters more than remembering individual purchase prices.
When should I average down on a stock?
Averaging down means buying more shares after a price drop, which lowers your weighted average price if the later purchase price is below your current cost basis. The calculator shows the math, but it does not decide whether adding to a position is appropriate.
Before adding to a losing position, compare the new average price with your risk plan, portfolio size, and the latest company information. A lower price can improve the arithmetic of the position, but it can also reflect real deterioration in the business or market outlook.
How does a stock average calculator work?
A stock average calculator uses weighted average math. It multiplies each purchase price by the number of shares bought, adds every purchase cost together, then divides that total cost by total shares owned.
This method handles uneven purchases correctly. A 500-share order has five times the weight of a 100-share order, so the larger trade has a larger effect on your average share price.
Average down vs. dollar-cost averaging
Average down calculations focus on what happens when you add shares below your current average price. Dollar-cost averaging is broader: it usually means investing a set amount on a schedule regardless of short-term price movement.
If you want to model scheduled contributions over time, use the DCA Calculator. If you want the average price of actual share purchases, this stock average calculator is the right tool.
Your Privacy is Protected
All calculations run entirely in your browser. We never collect, store, or transmit any data you enter into this calculator. There are no APIs, no server requests, and no logs - your financial information stays on your device and disappears when you close the page.
For informational and educational purposes only — not investment advice.