Stock Average (Average Down) Calculator
Average down across up to five buys: enter shares and price for each lot to get your share-weighted cost basis and break-even price.
Enter each buy — the number of shares and the price you paid. The calculator blends them into one average cost per share, which is also your break-even price.逐笔填入你的买入——股数与成交价。计算器会把它们合成一个平均成本价，这也就是你的保本价。
Fill in at least two lots to blend your average cost.至少填入两笔买入即可计算平均成本。
- Total shares总股数
- Total cost总成本
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- Break-even price保本价
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- Lots counted计入笔数
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Your average cost per share is the total dollars spent divided by the total shares held — not the average of the prices. A buy of 100 shares at $50 and another 100 at $40 blends to $45.00, because both lots are the same size; weight the price by the shares and the number falls out on its own. That blended figure is also your break-even: the price the stock must reclaim before the whole position is above water.你的每股平均成本，是总投入金额除以总持有股数——而不是各价格的简单平均。以 $50 买入 100 股、再以 $40 买入 100 股，合成后为 $45.00，因为两笔规模相同；用股数为价格加权，结果自然得出。这个合成价也是你的保本价：股价必须重回该位，整个仓位才回本。
01The formula公式
Total cost = Σ ( shares × price )总成本 = Σ ( 股数 × 价格 )
Average cost = Total cost ÷ Total shares平均成本 = 总成本 ÷ 总股数
Break-even price = Average cost保本价 = 平均成本
This is a share-weighted mean. A large lot pulls the average toward its price and a small one barely moves it — which is why adding a few shares at a much lower price lowers your basis only a little, while a big add near the lows lowers it a lot.这是一个按股数加权的平均值。大笔买入会把均价拉向它的价格，小笔则几乎不动它——这就是为什么在低位补几股只能略微拉低成本，而在低位重仓补入才能大幅拉低成本。
02A worked example一个算例
Suppose a trader buys 100 shares at $50.00, then the stock falls and they add 100 more at $40.00.假设一位交易者以 $50.00 买入 100 股，随后股价下跌，又在 $40.00 补入 100 股。
- Total shares = 100 + 100 = 200总股数 = 100 + 100 = 200
- Total cost = (100 × 50) + (100 × 40) = $9,000总成本 = (100 × 50) + (100 × 40) = $9,000
- Average cost = 9,000 ÷ 200 = $45.00平均成本 = 9,000 ÷ 200 = $45.00
- Break-even = $45.00 — the stock only needs to climb from $40 back to $45, not all the way to $50, for the blended position to break even.保本价 = $45.00——股价只需从 $40 回升到 $45，而非一路涨回 $50，整个仓位即可回本。
Averaging down does two things at once: it lowers the basis and it enlarges the position. The lower break-even is the appealing half; the bigger position is the half that gets ignored.摊低成本同时做了两件事：拉低成本价，并且放大仓位。更低的保本价是诱人的一半；更大的仓位则是常被忽略的另一半。
03The common trap常见陷阱
A lower average cost feels like progress, but it is only progress if the reason you bought is still intact. Adding shares because the price fell — rather than because the thesis got stronger — turns one losing position into a larger losing position, and quietly makes it the biggest weight in the book. The number this tool prints goes down; the risk goes up. Decide in advance how much you are willing to commit to a name in total, and let the average cost be a consequence of that plan, not the reason to keep adding.更低的平均成本让人感觉在进步，但只有当你当初买入的理由依然成立时，它才算进步。因价格下跌——而非因逻辑变强——而补仓，只会把一个亏损仓位变成更大的亏损仓位，并悄悄让它成为账簿中最重的一笔。本工具打印的数字在下降，风险却在上升。请事先决定你愿意在一只标的上总共投入多少，让平均成本成为该计划的结果，而非继续加码的理由。
04Where this breaks它的局限
The arithmetic is exact, but it describes a bare cost basis — not the full picture a real account carries. A few honest limits:这套算法在数学上是精确的，但它描述的只是一个裸露的成本价——而非一个真实账户所承载的全貌。几点诚实的局限：
- Fees and commissions. This blends the price you paid; it does not add per-trade fees or bid-ask slippage. On thin names or many small lots, your true basis sits a little above what this shows.费用与佣金。本工具合成的是你的成交价，不包含每笔手续费或买卖价差滑点。在流动性差的标的或多笔小额买入上，你的真实成本会略高于此处显示。
- Cost-basis method for taxes. Brokers may track lots by FIFO, specific-identification, or average cost, and the method changes your taxable gain when you sell part of the position. This calculator shows the plain share-weighted average only.报税的成本计算法。券商可能按先进先出、指定批次或平均成本来记账，而在你卖出部分仓位时，所选方法会改变你的应税收益。本计算器仅展示朴素的按股加权平均。
- Break-even is not a target. Reclaiming your average cost only means the loss is erased — it is not a reason to sell, nor a promise the price will get there. Size and thesis decide that, not the basis line.保本价不是目标价。重回平均成本只意味着亏损被抹平——它既不是卖出的理由，也不保证价格会到那里。决定这一切的是仓位与逻辑，而非成本线。
Averaging down lowers your cost and raises your size at the same time. A lower break-even is only worth having if the reason you own the stock is still true.摊低成本会在拉低成本价的同时放大你的仓位。只有当你持有这只股票的理由依然成立时，更低的保本价才值得拥有。
Turn a cost basis into a plan with the 用 position size calculator仓位计算器, or measure a completed trade with the 把成本价化为计划，或用 trade profit calculator交易盈亏计算器.衡量一笔已完成的交易。