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Stock Average Cost Calculator (Averaging Down/Up)

Blend an existing stock position with a new purchase into one weighted-average cost per share, plus the unrealized gain or loss at any price you check against.

New average cost per share
$43.33
Total shares held
150
Total cost basis
$6,500.00
Change in average cost
-13.33%
Unrealized gain/loss at current price
-$500.00
Unrealized gain/loss %
-7.69%

How it works

Averaging down (or up) is just a weighted average: blend the cost of every share you hold into one number. NewAverageCost = (ExistingShares × ExistingAverageCost + NewShares × NewPrice) ÷ (ExistingShares + NewShares). Buying more shares at a price below your existing average pulls that average — and your break-even price — down; buying more above it pushes the average up. Entering 0 existing shares treats this as a first purchase, where the new average cost is simply the new price.

The unrealized gain or loss is then just (CurrentPrice − NewAverageCost) × TotalShares, with the percentage version dividing that difference by the new average cost instead of the original purchase price — because after averaging, the new blended cost is what you're actually measuring your position against, not either individual lot.

FAQ

Does averaging down actually lower my risk?

It lowers your break-even price, which means a smaller rebound gets you back to even — but it also means you now have more money committed to a position that has already moved against you. This calculator shows the arithmetic of the new cost basis; it doesn't tell you whether adding to a losing position is the right call for a given stock, which depends on reasons this calculator has no way to know.

Does this include broker commissions or fees?

No — it works purely from the share counts and prices you enter. If your broker charges a flat or per-share commission, add it to the purchase price you enter (price plus commission per share) to fold it into the average cost.

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