Stock Average Calculator
Find your weighted-average cost basis across every purchase you’ve made on a stock — the breakeven price that decides whether a sale books a gain or a loss.
Add one row per purchase, enter price and number of shares, and the calculator returns the weighted average. Pick a ticker first to prefill the latest market price into the first row.
Stock Average Calculator: Find Your Cost Basis
Updated April 2026
Key Points
- Your average cost per share (cost basis) is the weighted average of every purchase you have made.
- Calculate it as Total Money Spent / Total Shares Owned across all lots.
- Knowing the average is essential for tracking performance, planning sells, and reporting taxes.
What is a stock average?
When you buy the same stock at different prices and times, your “average price” is the single per-share figure that summarizes what you paid in total. Brokerages call this your cost basis. It is the breakeven point — sell above it and you book a gain, sell below it and you book a loss.
Formula for the weighted average
Average Cost = Σ (Price × Shares) / Σ Shares. The total dollars spent across every purchase, divided by the total shares owned. Each lot is weighted by its share count, so a 100-share buy moves the average more than a 10-share buy.
How to calculate the average price
List every purchase you have made: the price you paid and how many shares you bought. Sum the dollars spent, sum the shares, and divide. The calculator above does this automatically across as many holdings as you add.
- Lot 1 — first buy: price and number of shares.
- Lot 2, 3, … — every subsequent buy on the same ticker.
- Add reinvested dividends as additional small lots if you participate in a DRIP.
Worked example
You buy 10 shares at $100 = $1,000, then 30 shares at $50 = $1,500. Total cost: $2,500. Total shares: 40. Average cost: $2,500 / 40 = $62.50. The 30-share buy at $50 pulled your average down from $100 to $62.50 because it was a much larger lot.
Dollar-cost averaging vs averaging down
Dollar-cost averaging (DCA) is buying a fixed dollar amount on a fixed schedule regardless of price — a long-term discipline that smooths your entry over time. Averaging down is buying more shares after a sharp price drop to lower your average. DCA is mechanical and emotion-free; averaging down is a deliberate bet that the price decline is temporary. Use the same calculator for both — it does not care why you are buying.
How to use your average price
Compare your average to the current market price to see your unrealized gain or loss per share. Use it when planning a partial sell — selling shares above your average books a profit, selling below books a loss. Brokerages report your basis to the IRS on every taxable sale, so an accurate average matters for tax planning, especially around year-end harvesting.
Limitations
The simple weighted average ignores commissions, dividend taxes, and reinvestments. For a complete trade economics view including fees, dividends, and after-tax ROI, use our Stock Profit Calculator. The average is also irrelevant when the underlying business has changed — do not let a low average price keep you in a deteriorating company.
Track your basis, ignore the noise
Your average cost is one of the most useful numbers in your portfolio. It anchors your performance accounting, your sell decisions, and your tax reporting. Update it every time you add to a position.
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Frequently asked questions
How do I calculate the average price of a stock?
- Add up the total dollars spent across every purchase (price × shares per lot) and divide by the total number of shares you own. The result is your weighted-average cost per share. Buying more shares at a lower price drags the average down; buying at a higher price pushes it up.
What is dollar-cost averaging (DCA)?
- Dollar-cost averaging is the practice of investing a fixed dollar amount on a regular schedule, regardless of price. Over time you buy more shares when the price is low and fewer when it is high, which usually produces a lower average cost than trying to time the market.
What is averaging down?
- Averaging down means buying more shares of a stock you already own after the price has dropped. This lowers your average cost per share. The risk: if the stock keeps falling, you compound your loss. Averaging down works best when fundamentals are intact and the price decline is sentiment-driven, not structural.
Why is the average important?
- The average price is your cost basis. It’s the price the stock must rise above (after fees) before you book a profit, and it’s the figure your broker uses to compute realized gains and losses for tax purposes.
Does this calculator account for fees and dividends?
- No — it shows a clean weighted-average cost per share. To include broker commissions, taxes, and reinvested dividends in your trade economics, use our Stock Profit Calculator, which models the full ROI of an entry-and-exit position.
Should I include reinvested dividends in my average cost?
- Yes, if you participate in a DRIP. Each reinvested dividend buys additional shares at the prevailing price and updates your weighted-average cost. Most brokerages do this automatically and report your adjusted basis on your year-end statement.
How is the weighted average different from a simple average?
- A simple average just averages the prices of each lot, ignoring how many shares you bought. The weighted average factors in lot size — a 100-share buy moves the average more than a 10-share buy. The weighted average is the only one that matches your real cost basis.
Can the average cost be higher than the current market price?
- Yes, and that means you are sitting on an unrealized loss. Holding (or averaging down on) sound fundamentals is fine; doubling down on broken fundamentals is not. Decide based on the business, not your average cost.
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