Calculators
Stock average cost calculator
Averaging down changes two things at once: it lowers the price you need to get back to break-even, and it raises the amount you have at stake. This shows both, because the second one is the one people forget.
Your purchases
Weighted average cost
$42.80
250.00 shares for $10,700.
Position value
$10,500
Unrealised P/L
-$200.00
-1.87%
Break-even price
$42.80
+1.90% from here
Average = total spent ÷ total shares. This is a weighted average, not the average of the prices — a large purchase counts for more than a small one. Commissions are not included; add them to a lot's price if you want a true cost basis.
If you bought more
Both figures move at once. Watch the second one.
New average
$42.57
-$0.2286 vs now
Total at stake
$14,900
+$4,200 more committed
New loss / gain
-$200.00
-1.34%
| Purchase | Shares | Price | Cost | Weight | P/L now |
|---|---|---|---|---|---|
| #1 | 100.00 | $50.00 | $5,000 | 46.7% | -$800.00 |
| #2 | 150.00 | $38.00 | $5,700 | 53.3% | $600.00 |
| Total | 250.00 | $42.80 | $10,700 | 100.0% | -$200.00 |
What averaging down does and does not fix
It genuinely lowers the price at which the position gets back to even, and that is not nothing — a break-even 12% away is a very different proposition from one 30% away. What it cannot do is make the original decision better. The new average is a fact about your cost basis, not about the company, and the market has no memory of what you paid.
The panel on the right is there because the two consequences are always reported unevenly. Every calculator will happily show you the new, lower average. Far fewer show what happened to the total at stake at the same moment, and that number always moves the wrong way. A position down 20% on $5,000 and a position down 12% on $9,000 are not obviously an improvement on each other; the percentage got better and the dollars got worse, and only one of those is what you actually lose.
The specific trap is scale. Because the average is weighted, moving it meaningfully requires a purchase of comparable size to what you already hold — a small top-up barely shifts it. So the act of 'improving' the average pushes you towards doubling a position that is already losing money, which is how a mistake that was sized correctly becomes one that is not. If you were sizing by a fixed risk rule when you opened it, the addition has to fit inside the same rule, and usually it does not.
Where averaging down is defensible is when it was planned before the position existed — a scale-in with the lot sizes and price levels decided in advance, and a level at which the thesis is wrong and the whole thing gets closed. That is a different activity from adding because the position is red, even though the arithmetic on this page is identical for both.
Questions people ask about this
- How is the average price calculated?
- Total money spent divided by total shares held — a weighted average, not the average of the prices. Buying 10 shares at $100 and 90 shares at $10 gives an average of $19, not $55, because the second purchase is nine times the size of the first.
- Does a lower average cost mean I am doing better?
- No. Averaging down lowers the break-even price and raises the position size at the same time, so the percentage loss shrinks while the dollar loss grows. The calculator shows both figures side by side for exactly this reason.
- Should fees and commissions go in?
- If you want a true cost basis, yes — add them to the amount spent on each lot. For most US brokers the commission is now zero and the difference is noise, but for a small position with a fixed fee it can move the average by a percent or more.
Sources and method
- Data
- None. This tool sends nothing anywhere — every figure is computed in your browser from the values you type, and no input is stored, logged or transmitted.
- How it was calculated
- Weighted average cost = total spent ÷ total shares, computed in your browser from the lots you enter. Nothing is stored or uploaded. Commissions are not included unless you fold them into a lot's price.
- How often it changes
- Never. The formula is fixed; the answer changes only when you change an input.
- Citing this page
Free to quote — please link rather than copy the table.
Plutux. "Stock average cost calculator." https://plutux.ai/resources/tools/stock-average-calculator
Historical figures for information only — not investment advice, and not a forecast.
Related tools
- Position sizeWork backwards from the loss you are willing to take to the number of shares, and check what that position does to your account if it gaps.
- CAGRTurn a starting value, an ending value and a number of years into a compound annual growth rate — and see what the same total return looks like over other horizons.
- Drawdown recoverySee the gain required to get back to even after a loss, and how many years of a given return that takes.
Plutux is not an investment adviser. Market data and AI-generated analysis are for information and education only, not investment advice. Disclaimer