Stock Average-Down Cost Basis Calculator
Add a second lot to a losing position and see your new blended cost basis, break-even price, and how far the stock must recover to get you whole.
How it works
New basis = (shares₁·price₁ + shares₂·price₂ + fees) ÷ total shares · Move to break even % = (basis − price) ÷ price × 100
Averaging down lowers your cost basis by adding shares at a price below your original average, so the whole position needs a smaller bounce to turn profitable. It is a mathematical fact, not a strategy on its own — you are also putting more money into a position that is already moving against you, so the lower break-even only helps if the thesis is still intact.
Worked example
100 shares bought at $50 cost $5,000. Adding 100 shares at $30 costs $3,000, so total cost is $8,000 over 200 shares — a $40 basis, down from $50. At a $35 market price the position is down $1,000 (−12.5%) and needs a 14.3% rise to reach the $40 break-even.
Frequently asked questions
How is this different from a plain averaging calculator?
It folds in commissions and your current market price, then shows the exact percentage the stock must recover from today to reach your new break-even — the number that actually decides whether averaging down was worth it.
Does averaging down guarantee a smaller loss?
No. It lowers your per-share break-even, but it increases the dollars at risk. If the stock keeps falling you lose more in total than if you had not added, so it only makes sense when your reason for owning the stock still holds.
Do commissions really matter?
On small lots or high-fee brokers they nudge your break-even higher because they are part of total cost. On zero-commission trades you can leave the field at 0 and the basis is just the share-weighted average price.
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Educational estimate, not investment advice. Trading involves risk of loss.