Calculator Panel
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Enter your values above and click Calculate.
What This Calculator Does
This calculator determines the combined average buy price per share for multiple purchases. It prevents the common error of calculating a simple average of buy prices rather than a volume-weighted average.
How to Use This Calculator
Enter the purchase price per share and number of shares for up to three separate transactions. Click Calculate to find your total share count, aggregate cost basis, and final weighted average price per share.
How the Calculation Works
The underlying math engine processes your inputs using exact formulas. This systematic approach ensures professional, institutional-grade calculation precision:
Mathematical Formula
Formula Legend:
- · P1, P2, P3 = Purchase Prices for transaction 1, 2, and 3 respectively.
- · Q1, Q2, Q3 = Shares purchased in transaction 1, 2, and 3 respectively.
Practical Example
Suppose you buy 50 shares of stock at $100 in your first buy, and 150 shares at $80 in your second buy:
Step-by-Step Mathematical Walkthrough:
- 1 First, find cost basis for buy 1: 50 shares * $100 = $5,000.
- 2 Second, find cost basis for buy 2: 150 shares * $80 = $12,000.
- 3 Aggregate the total cost and total shares: $5,000 + $12,000 = $17,000; 50 + 150 = 200 shares.
- 4 Divide total cost by total shares: $17,000 / 200 = $85.00 average price per share.
Important Assumptions & Notes
- All purchase entries represent purchases of the exact same stock ticker.
- Commissions are excluded or can be added to purchase prices directly.
Common Mistakes or Considerations
- Calculating a simple average (e.g. ($100 + $80)/2 = $90) which completely ignores share volume weights.
Frequently Asked Questions
What is averaging down?
The practice of buying more shares of a stock as its price declines, which lowers your average purchase price per share and decreases the break-even target.
Can I add transaction fees here?
Yes, including purchase transaction fees in your average price calculation provides a more precise cost basis for tax and return tracking.
How is a weighted average cost calculated?
By dividing the total dollar amount spent across all purchase transactions (including fees) by the total number of shares purchased.
Why is the average cost basis important for taxes?
Your average cost basis determines the taxable capital gain or loss when you sell shares. An accurate cost basis prevents you from overpaying taxes.
Does averaging down guarantee future profitability?
No. While averaging down lowers your break-even price, if the stock's underlying business is permanently declining, buying more shares will simply increase your total losses.