股票平均成本计算器
免费股票平均成本计算器，支持无限次购买记录。计算每股平均成本、总持仓成本、盈亏平衡价格以及未实现盈亏。适用于股票、ETF、加密货币和任何资产。
Stock Average Calculator
Enter each purchase to calculate your average cost per share, total investment, and break-even price.
Frequently Asked Questions
股票平均成本计算器是如何工作的？
股票平均成本（加权平均价）= 总投入金额 / 总持有股数。例如，第一次以 $50 买入 100 股，第二次以 $40 买入 150 股：总成本 = $5,000 + $6,000 = $11,000；总股数 = 250 股；平均成本 = $11,000/250 = $44/股。
什么是摊低成本（Averaging Down）？
摊低成本是指在股价下跌后买入更多股份，从而降低整体持仓成本的策略。虽然能降低盈亏平衡点，但如果公司基本面恶化，这种策略会加大损失。摊低成本应基于对公司长期价值的深入判断，而非单纯追低。
如何计算持仓盈亏？
未实现盈亏 = (当前市价 - 平均成本) × 总股数；盈亏百分比 = (当前市价 - 平均成本) / 平均成本 × 100%。本计算器输入当前市价后，会自动计算每股盈亏、总盈亏金额和盈亏百分比。
计算股票成本时是否应包含手续费？
是的，手续费应计入成本以准确计算实际收益。调整后成本 = (总买入金额 + 所有手续费) / 总持有股数。本计算器支持在每次交易中输入手续费，确保平均成本计算的准确性。
How to Calculate Average Stock Price
The Stock Average Calculator is an essential tool for investors who need to compute their average cost per share after making multiple purchases at different prices. Whether you are dollar cost averaging into an index fund or averaging down on a single stock, this calculator shows your weighted average cost basis, break-even price, and unrealized gain or loss in real time.
Table of Contents
Stock Average Formula
The weighted average cost per share is calculated using these formulas:
Total Shares:
Total Shares = Shares from Purchase 1 + Shares from Purchase 2 + ... + Shares from Purchase N
Total Investment:
Total Investment = (Price₁ × Shares₁ + Fee₁) + (Price₂ × Shares₂ + Fee₂) + ... + (Priceₙ × Sharesₙ + Feeₙ)
Average Cost Per Share:
Average Cost = Total Investment ÷ Total Shares
Break-Even Price:
Break-Even Price = Average Cost Per Share (the price the stock must reach for you to have zero profit/loss)
Step-by-Step Calculation Example
Initial Purchase:
- 100 shares at $50.00 per share
- Investment: 100 × $50 = $5,000
Second Purchase:
- 50 shares at $45.00 per share
- Investment: 50 × $45 = $2,250
Result:
- Total Shares: 100 + 50 = 150
- Total Investment: $5,000 + $2,250 = $7,250
- Average Cost: $7,250 ÷ 150 = $48.33 per share
- Break-Even Price: $48.33
Average Down Calculator Example
You bought 200 shares of XYZ at $75 ($15,000). The stock drops to $50, and you buy 100 more shares ($5,000).
- Total Investment: $15,000 + $5,000 = $20,000
- Total Shares: 200 + 100 = 300
- New Average Cost: $20,000 ÷ 300 = $66.67 per share
- Cost Reduction: ($75 − $66.67) ÷ $75 = 11.1%
- Break-Even Price: $66.67 (need 33.3% recovery from $50 vs 50% without averaging down)
By averaging down, you reduced the recovery needed from a 50% gain back to $75 to just a 33.3% gain to $66.67.
What Is Averaging Down in Stocks?
Averaging down is an investment strategy where you purchase additional shares of a stock after its price has fallen, thereby lowering your overall average cost per share. The goal is to reduce your break-even price so that you need a smaller price recovery to return to profitability. For example, if you originally bought shares at $100 and the price drops to $60, buying more at $60 pulls your average cost below $100 — meaning you no longer need the stock to fully recover to $100 to break even.
Averaging down is one of the most debated strategies in investing. When used correctly on fundamentally sound companies experiencing temporary setbacks, it can significantly improve long-term returns. However, when used on companies with deteriorating business fundamentals, it can compound losses. The key distinction is whether the price drop is a temporary dislocation or a reflection of genuine business decline.
When to Average Down
- Strong fundamentals remain intact: earnings, revenue growth, and balance sheet are healthy despite the price decline
- Temporary market downturn: broad market selloff or sector rotation rather than company-specific bad news
- Your original investment thesis is unchanged: the reasons you bought the stock still hold true
- Position sizing allows it: adding shares will not make the position an outsized portion of your portfolio
- Long time horizon: you can afford to wait for the recovery without needing the capital
Risks of Averaging Down
- Catching a falling knife: the stock may continue to decline, amplifying your losses
- Overconcentration: repeatedly buying the same stock can leave your portfolio dangerously undiversified
- Confirmation bias: you may convince yourself the stock is undervalued simply because you already own it
- Opportunity cost: capital tied up in a losing position could be invested in better-performing assets
- Emotional decision-making: the desire to “get back to even” can override objective analysis
Averaging Down vs Dollar Cost Averaging
While both strategies involve making multiple purchases, they differ in approach and intent:
- Dollar Cost Averaging (DCA) is a systematic strategy where you invest a fixed dollar amount on a regular schedule — weekly, biweekly, or monthly — regardless of whether the price is up or down. The goal is to remove emotion and timing from the equation. DCA reduces the risk of investing a large sum at a market peak and works well for broad market index funds.
- Averaging Down is a deliberate, discretionary decision to buy more of a specific stock at a lower price. It is conviction-driven: you believe the current price undervalues the company and you actively choose to increase your position. Unlike DCA, it concentrates your investment in a single stock rather than spreading it over time.
- Can they be combined? Yes. Many investors use DCA as their default strategy for index fund contributions while selectively averaging down on individual stock positions they have high conviction in.
Understanding Cost Basis
Your cost basis is the total amount you paid for an investment, including the purchase price plus any commissions or fees. The IRS uses your cost basis to calculate capital gains or losses when you sell: Capital Gain = Sale Price − Cost Basis. A higher cost basis means lower taxable gains, while a lower cost basis means higher taxable gains. Accurately tracking your cost basis is essential for tax reporting and investment performance measurement.
Cost Basis Methods: FIFO, LIFO, and Average Cost
- FIFO (First In, First Out): The oldest shares you purchased are considered sold first. If your earliest purchases were at the lowest prices, FIFO will result in the highest capital gains (and the highest tax bill). FIFO is the default method used by most brokerages.
- LIFO (Last In, First Out): The most recently purchased shares are sold first. If your most recent purchases were at higher prices, LIFO can minimize short-term capital gains and reduce your immediate tax burden.
- Average Cost: Your total investment is divided by the total number of shares to produce a single average cost per share. This is the simplest method and is required for mutual fund investors. Many brokers use this as the default for convenience.
How Cost Basis Affects Your Taxes
Choosing the right cost basis method can significantly affect your tax bill. Consider this scenario: you made three purchases of the same stock at $40, $50, and $60 per share, and you now want to sell one lot at $55.
- FIFO: sells the $40 shares first → $15/share gain (taxable)
- LIFO: sells the $60 shares first → $5/share loss (tax deduction)
- Average Cost: average is $50 → $5/share gain (taxable, but smaller than FIFO)
Consult a tax professional to determine which method is most advantageous for your situation. Your broker reports your chosen method on Form 1099-B.
Stock Average Cost Examples
Example 1: Averaging Down a Tech Stock
Initial Position:
- 100 shares at $150.00 per share
- Investment: $15,000
Price drops — you buy more:
- 50 shares at $120.00 per share ($6,000)
- 50 shares at $100.00 per share ($5,000)
Result:
- Total Shares: 200
- Total Investment: $26,000
- Average Cost: $26,000 ÷ 200 = $130.00 per share
- You reduced your break-even from $150 to $130 — a 13.3% reduction
Example 2: Dollar Cost Averaging Over 6 Months
Monthly investment of $500 in ABC stock:
| Month | Price | Shares | Cost |
|---|---|---|---|
| Month 1 | $50.00 | 10.00 | $500 |
| Month 2 | $45.00 | 11.11 | $500 |
| Month 3 | $40.00 | 12.50 | $500 |
| Month 4 | $42.00 | 11.90 | $500 |
| Month 5 | $48.00 | 10.42 | $500 |
| Month 6 | $52.00 | 9.62 | $500 |
- Total Invested: $3,000
- Total Shares: 65.55
- Average Cost: $3,000 ÷ 65.55 = $45.77 per share
The simple average of the six prices is $46.17, but DCA gave you a lower average of $45.77 because you bought more shares when prices were low.
Example 3: Impact of Fees on Average Price
Without fees:
- 100 shares at $50 = $5,000 total
- Average cost: $50.00 per share
With $9.99 fee per trade:
- 100 shares at $50 + $9.99 fee = $5,009.99 total
- Average cost: $5,009.99 ÷ 100 = $50.10 per share
Over 10 separate trades:
- 1,000 shares at $50 (100 per trade) + 10 × $9.99 = $50,099.90 total
- Average cost: $50,099.90 ÷ 1,000 = $50.10 per share
- Fees alone added $99.90 to your total investment
While modern brokerages have largely eliminated commissions, fees can still apply to OTC stocks, options, and cryptocurrency exchanges. Always factor them into your cost basis calculation.