Two ways to use this calculator
The first mode answers “if I buy more, what happens to my average?” Enter the shares you already own and your current average cost, then the shares and price of the buy you’re considering. You’ll get your new average cost (which is also your break-even price) and how far the price has to move from your new buy to get back to break-even.
The second mode works backward: “how many shares do I need to reach a target average?” Give it your current position, the price you could buy at, and the average you’re aiming for, and it solves for the exact number of shares and the cash required.
The math
A new average is just a weighted average of every share you hold:
new average = total cost ÷ total shares. To find the shares needed to reach a target
average T by buying at price P, the calculator solves
n = shares × (average − T) ÷ (T − P). That equation only has a valid answer when the
buy price is below the target and the target is below your current average — because buying more
shares can only pull your average down, and only toward a price you’re actually paying.
When the numbers don’t allow it, the tool tells you instead of returning a misleading figure.
A worked example
You own 100 shares at an average of $10. You buy 100 more at $8. Your total cost is $1,000 + $800 = $1,800 across 200 shares, so your new average is $9.00. From the $8 you just paid, the price needs to rise 12.5% to reach that $9 break-even. If instead you had a target average of $9 in mind, the calculator would tell you that buying 100 shares at $8 gets you there exactly.
What to keep in mind
- Lowering your average also raises your total position size — and your risk.
- You can only average down by buying below your current average.
- Break-even is the same as your average cost; it ignores commissions and taxes.
TradeCaliper is a planning and education tool, not financial advice.