Stock Average Price Calculator
Calculate your average cost basis and see how additional purchases affect it. Currently calculating in US Dollar.
Total: $1,000
Total: $1,275
Average Cost Per Share
$91
25 shares | Total invested: $2,275
Unrealized P/L at $95
+$100
+4.40% | Current value: $2,375
Total Shares
25
Total Cost
$2,275
Break-Even Price
$91
Profit at Target
+$475
+20.88% at $110
New Average
$86
-$5 per share
New Total Shares
45
New Total Cost
$3,875
New Break-Even
$86
| Purchase | Shares | Price/Share | Total Cost | % of Holdings | Current Value | P/L |
|---|---|---|---|---|---|---|
| #1 | 10 | $100 | $1,000 | 40.0% | $950 | -$50 |
| #2 | 15 | $85 | $1,275 | 60.0% | $1,425 | +$150 |
| Total | 25 | $91 | $2,275 | 100% | $2,375 | +$100 |
What is a Stock Average Price Calculator?
A stock average price calculator computes your weighted average cost basis across multiple purchases of the same stock. Because stock prices fluctuate, most investors end up buying the same stock at several different prices over time. The average cost per share is not simply the arithmetic mean of those prices — it must be weighted by the number of shares purchased at each price.
Knowing your average cost basis is essential for three reasons. First, it tells you your precise break-even price — the stock must be above this level for your position to be profitable. Second, it determines your unrealized profit or loss at any current market price. Third, it is the figure the IRS uses to calculate your taxable capital gain or loss when you sell, making it a critical number for tax planning.
This calculator also includes a what-if analyzer: enter a hypothetical new purchase — how many shares at what price — and instantly see how it would shift your average, total cost, and break-even price. This is the core tool for evaluating whether to average down on a losing position or average up into a winner.
How to Use This Calculator
Enter Your Purchase History
Add each lot you purchased: the number of shares and the price per share you paid. Use the Add button to add as many lots as you need. The calculator handles any number of purchases across any date range.
Set the Current Market Price
Enter the stock's current trading price. This is used to calculate your unrealized profit or loss and current portfolio value across all your lots. Update it whenever you want a fresh P/L snapshot.
Model a New Purchase (What-If)
In the "What If I Buy More?" section, enter the shares and price of a hypothetical new purchase. The result panel immediately shows your new weighted average, new break-even price, and updated total cost — before you commit to the trade.
Set a Target Sell Price
Enter the price at which you plan to sell. The calculator shows your projected profit at that target, both in dollar terms and as a percentage return on your total cost basis — a quick way to evaluate whether a price target justifies holding.
How Average Cost Basis Is Calculated
All key outputs are derived from three core formulas:
1. Weighted Average Cost Per Share
Avg Cost = Total Amount Invested ÷ Total Shares Owned
Total Amount Invested = ∑(Shares × Price) across all purchase lots
2. Unrealized Profit / Loss
Unrealized P/L = (Current Price − Avg Cost) × Total Shares
3. Return Percentage
Return % = ((Current Price − Avg Cost) ÷ Avg Cost) × 100
4. New Average After Additional Purchase
New Avg = (Total Invested + New Shares × New Price) ÷ (Total Shares + New Shares)
Worked example: You buy 10 shares at $100 (total $1,000), then 15 shares at $80 (total $1,200). Total invested = $2,200. Total shares = 25. Weighted average = $2,200 ÷ 25 = $88.00. At a current price of $90, unrealized P/L = ($90 − $88) × 25 = +$50 (+2.27%). If you now buy 20 more shares at $75: new total invested = $2,200 + $1,500 = $3,700. New total shares = 45. New average = $3,700 ÷ 45 = $82.22.
Example Averaging Scenarios
Tips for Managing Your Cost Basis
Averaging down requires conviction, not hope
Before buying more of a declining stock, ask whether the fundamental thesis that made you buy it still holds. Averaging down on a structurally broken business simply compounds losses. Only add to positions where the price drop is caused by temporary sentiment, not deteriorating fundamentals.
Know the three cost basis methods before you sell
The IRS allows three methods: FIFO (sells oldest shares first), LIFO (sells newest first, allowed only for crypto), and Specific Identification (you choose which lot to sell). Specific Identification is most powerful — it lets you harvest losses or defer gains by choosing the highest-cost lot to sell first.
Track wash-sale rules when harvesting losses
If you sell a stock at a loss and repurchase the same or "substantially identical" security within 30 days before or after the sale, the IRS disallows the loss deduction under the wash-sale rule. The disallowed loss is added to the cost basis of the new purchase instead.
Reinvested dividends raise your cost basis
If you participate in a DRIP (Dividend Reinvestment Plan), each dividend reinvestment adds shares at that day's price, raising your total cost basis and lowering your average cost per share slightly over time. Track these lots carefully to avoid overpaying capital gains taxes when you sell.
Use the what-if tool before placing the order
Before adding to a position, use this calculator's what-if section to see the exact average you'd achieve at various prices and share counts. This prevents the common mistake of buying too few shares at a lower price to meaningfully move the average.
Consider position sizing before averaging down
If a stock already represents 10% of your portfolio and has fallen 30%, averaging down will increase concentration risk further. Set a maximum position size limit before you start a position and respect it when deciding whether averaging down is appropriate.
Dollar Cost Averaging, Averaging Down, and Cost Basis Methods
Dollar cost averaging (DCA) is the strategy of investing a fixed dollar amount at regular intervals — weekly, monthly, or quarterly — regardless of the stock's current price. Because a fixed dollar amount buys more shares when prices are low and fewer when prices are high, DCA naturally lowers the average cost per share over time compared to investing the entire amount at a single point. It is the default strategy in most 401(k) plans, where payroll deductions invest automatically every pay period.
Averaging down is a deliberate strategy of buying additional shares of a stock that has declined in price since your initial purchase, with the explicit goal of lowering your average cost basis. This reduces the price at which your overall position becomes profitable. The mathematical appeal is real: if you bought 10 shares at $100 and buy 20 more at $70, your average drops from $100 to $80 — a 20% reduction in break-even price. The risk is equally real: you are increasing your exposure to a position that the market is currently pricing lower, and if the decline is driven by genuine business deterioration, averaging down simply throws good money after bad.
Cost basis reporting and taxes: Since 2011 (equities) and 2012 (mutual funds), brokers are required by law to report your cost basis to the IRS on Form 1099-B when you sell. The default method at most brokers is FIFO. However, you can elect Specific Identification at the time of sale to choose which specific lots you are selling — this is typically the most tax-efficient approach because it lets you sell the highest-cost shares first to minimize taxable gains, or deliberately sell loss lots for tax-loss harvesting. The IRS Publication 550 covers all cost basis methods in detail.
Effect of Averaging Down: 100 Shares Bought at $100
| Additional Shares Bought At | Additional Shares | New Average Cost | Break-Even Drop |
|---|---|---|---|
| No additional purchase | — | $100.00 | 0% |
| $90 | 100 | $95.00 | −5.0% |
| $80 | 100 | $90.00 | −10.0% |
| $70 | 100 | $85.00 | −15.0% |
| $70 | 200 | $80.00 | −20.0% |
| $60 | 200 | $73.33 | −26.7% |
For official guidance on cost basis methods and wash-sale rules, see IRS Publication 550: Investment Income and Expenses. For broker-reported cost basis rules, the FINRA cost basis reporting guide explains what your broker must report to the IRS and how to choose your method.
Frequently Asked Questions
What is cost basis and why does it matter?
Cost basis is the total amount you paid to acquire your shares, including the purchase price and any commissions or fees. It is your starting point for calculating capital gains or losses when you sell. If you sell shares for more than your cost basis, you have a capital gain (taxable). If you sell for less, you have a capital loss (which can offset other gains). Accurately tracking your cost basis across multiple purchases is essential for correct tax reporting.
What is the difference between averaging down and dollar cost averaging?
Dollar cost averaging (DCA) is a systematic, pre-planned strategy of investing a fixed dollar amount at regular intervals regardless of price — you are not reacting to price moves, you are simply investing consistently over time. Averaging down is a reactive strategy: you intentionally buy more shares specifically because the price has dropped since your initial purchase, with the goal of lowering your break-even price. DCA is generally considered a passive, low-stress approach, while averaging down is an active tactical decision that requires conviction in the underlying investment.
How does the IRS calculate my capital gain when I sell?
Your capital gain = Sale Price − Cost Basis. If you have purchased shares in multiple lots at different prices, the IRS requires you to specify which shares you are selling. Under the default FIFO method, you are assumed to sell the oldest shares first. Under Specific Identification, you can choose which lot to sell — this flexibility lets you minimize your taxable gain by selling the highest-cost shares first, or strategically harvest a loss by selling a specific lower-cost lot. You must specify your chosen lot to your broker at the time of sale.
What is the wash-sale rule and how does it affect averaging down?
The wash-sale rule (IRS Section 1091) disallows a capital loss deduction if you sell a security at a loss and buy a "substantially identical" security within 30 days before or after the sale. This prevents investors from manufacturing tax losses while maintaining their market exposure. If a wash sale occurs, the disallowed loss is added to the cost basis of the replacement shares, effectively deferring the loss until those shares are sold. This rule applies to stocks, ETFs, and options but not cryptocurrency (as of current rules).
Should I average down on a losing stock?
Only if two conditions are met: (1) the fundamental investment thesis that made you buy the stock originally still holds — the decline is a price reaction, not a reflection of deteriorating business quality; and (2) adding to the position does not violate your portfolio diversification rules or position size limits. Averaging down on a stock that has declined because of genuine business problems is one of the most common and costly mistakes retail investors make. Use this calculator to model the exact math before committing capital.
Are reinvested dividends included in my cost basis?
Yes. When dividends are reinvested through a DRIP, each reinvestment purchases new shares at the current market price and creates a new tax lot with its own cost basis at that price. These lots must be tracked individually just like manual purchases. Most brokers track DRIP lots automatically and report them on your 1099-B. Failing to include DRIP lots in your cost basis results in double taxation — you already paid income tax on the dividend when it was paid, so that amount should be included in your basis.
Related Calculators
Stock Profit Calculator
Calculate profit and loss on stock trades
Investment Calculator
Project growth with regular contributions
ROI Calculator
Calculate return on any investment
Compound Interest Calculator
Model long-term portfolio compounding
Rule of 72 Calculator
Estimate how long to double your money
Capital Gains Tax Calculator
Estimate taxes owed when you sell