Stock Average Down Calculator — Cost Basis Tool
Find your average cost per share after buying stock at different prices and dates, with total shares and break-even price.
Reviewed by Sahil, Senior Finance & Tax Editor
Formula
Average Price = Total Cost / Total Shares = Sum(Shares_i x Price_i) / Sum(Shares_i)
Where Shares_i and Price_i represent the number of shares and price per share for each individual purchase transaction. This is a weighted average that gives larger purchases proportionally more influence on the final average. The result equals your break-even price.
Worked Examples
Example 1: Averaging Down on a Growth Stock
Problem:You bought 50 shares at $100, then 30 more at $85 during a dip, then 20 more at $120 after a bounce. Current price is $110. What is your average cost and profit/loss?
Solution:Purchase 1: 50 x $100 = $5,000\nPurchase 2: 30 x $85 = $2,550\nPurchase 3: 20 x $120 = $2,400\nTotal cost = $5,000 + $2,550 + $2,400 = $9,950\nTotal shares = 50 + 30 + 20 = 100\nAverage price = $9,950 / 100 = $99.50\nCurrent value = 100 x $110 = $11,000\nUnrealized gain = $11,000 - $9,950 = $1,050 (+10.55%)
Result:Average price: $99.50 | Current value: $11,000 | Unrealized gain: $1,050 (+10.55%)
Example 2: Dollar Cost Averaging Monthly
Problem:You invested $1,000 per month for 4 months at prices of $50, $45, $55, and $48. Current price is $52.
Solution:Month 1: $1,000 / $50 = 20 shares\nMonth 2: $1,000 / $45 = 22.22 shares\nMonth 3: $1,000 / $55 = 18.18 shares\nMonth 4: $1,000 / $48 = 20.83 shares\nTotal shares = 81.23\nTotal invested = $4,000\nAverage price = $4,000 / 81.23 = $49.24\nSimple price average = ($50+$45+$55+$48) / 4 = $49.50\nCurrent value = 81.23 x $52 = $4,224.09\nGain = $224.09 (+5.60%)
Result:Average price: $49.24 | 81.23 shares | Current value: $4,224 | Gain: $224 (+5.60%)
Frequently Asked Questions
What is a stock average price and why does it matter?
The average stock price, also known as the cost basis or average cost per share, is the weighted average price you paid across all your purchases of a particular stock. It is calculated by dividing the total amount invested by the total number of shares owned. This number matters because it determines your break-even point and your profit or loss when you sell. For tax purposes, the IRS uses your cost basis to calculate capital gains or losses. If you bought 100 shares at $50 and later bought 50 more shares at $40, your average price is not simply $45 but rather (100 x $50 + 50 x $40) / 150 = $46.67 per share. Knowing your exact average price helps you make informed decisions about when to buy more or sell.
How does dollar cost averaging work?
Dollar cost averaging (DCA) is an investment strategy where you invest a fixed dollar amount at regular intervals regardless of the share price. When prices are high, your fixed amount buys fewer shares; when prices are low, the same amount buys more shares. Over time, this naturally results in a lower average cost per share compared to buying all shares at once, especially in volatile markets. For example, investing $500 per month over 6 months at prices of $100, $80, $90, $110, $70, and $95 would purchase 5, 6.25, 5.56, 4.55, 7.14, and 5.26 shares respectively, totaling 33.76 shares for $3,000, giving an average of $88.87 per share versus the simple price average of $90.83. DCA reduces the risk of investing a large sum at a market peak.
Should I average down on a losing stock?
Averaging down means buying additional shares of a stock that has declined in price to lower your average cost basis. This strategy can be profitable if the stock eventually recovers above your new lower average price. However, averaging down on a fundamentally deteriorating company is one of the most common and costly mistakes individual investors make. Before averaging down, honestly assess whether the price decline is temporary market noise or reflects genuine problems with the business such as declining revenue, mounting debt, or competitive threats. Professional investors follow a rule: only average down if you would buy the stock at the current price even if you did not already own shares. Never average down simply because you are emotionally attached to your original investment thesis or afraid to admit a mistake.
How do stock splits affect my average price?
Stock splits change your share count and price per share proportionally but do not change your total cost basis or investment value. In a 2-for-1 forward split, your shares double and the price per share halves, so your average cost per share also halves. If you owned 100 shares at an average of $200 (total cost $20,000) and the stock splits 2-for-1, you now own 200 shares at an average of $100 (total cost still $20,000). Reverse splits work the opposite way: a 1-for-10 reverse split means 1,000 shares at $1 become 100 shares at $10. Most brokerage platforms automatically adjust your cost basis after a split, but it is wise to verify the adjustment manually. Fractional shares resulting from odd-lot splits are typically paid out as cash by the company.
References
Reviewed by Sahil, Senior Finance & Tax Editor · Editorial policy