Investing
Stock Average Calculator
Buying more of a stock at a different price changes your average cost. Enter your two purchases — shares and price each — to see your blended average cost per share, total shares held, and total amount invested (your cost basis).
Formula shown below · Tested against worked examplesHow we verify
Average cost per share: $43.33
Average cost per share
$43.33
Your blended cost basis across both purchases.
- Total shares
- 150
- Total invested
- $6,500
- Break-even price
- $43.33
The price you need to sell at to break even.
Compare scenariosTry three values of one input
| First buy — shares | |||
|---|---|---|---|
| Average cost per share | $42.86 | $43.33+$0.47 | $43.75+$0.89 |
| Total shares | 140 | 150+10 | 160+20 |
| Total invested | $6,000 | $6,500+$500 | $7,000+$1,000 |
| Break-even price | $42.86 | $43.33+$0.47 | $43.75+$0.89 |
Every other input stays at the value you set above — currently 100 for first buy — shares. Differences are measured against the first column.
Saved scenariosSave this calculation
Saved in this browser only — no account, and nothing is sent to us. Clearing your browser data deletes them.
How this calculator works
Total invested = shares₁ × price₁ + shares₂ × price₂. Average cost = total invested ÷ total shares. The break-even price equals your average cost (before fees and taxes).
Covers two purchase lots; for more, add each lot's cost and shares the same way. It doesn't include trading commissions or taxes, which slightly raise your true break-even. Cost basis for tax purposes may also be affected by dividends and wash-sale rules.
Formula
Average = Σ (sharesᵢ × priceᵢ) ÷ Σ sharesᵢ- sharesᵢ
- Shares bought in purchase i
- priceᵢ
- Price paid in purchase i
A share-weighted average, so a large purchase moves it far more than a small one. This is your cost basis for tax unless you identify specific lots at sale — and specifying high-basis lots reduces the taxable gain.
What this assumes
- A weighted average cost basis across the purchases entered.
- It does not account for the specific-lot identification method, which can produce a better tax outcome on sale.
- Averaging down changes your cost basis, not the reason the price fell.
What changes this number
- Size of later purchases
- A large purchase at a low price moves the average far more than a small one.
- Why the price fell
- The question the calculator cannot answer, and the only one that matters before averaging down.
- Lot selection at sale
- Specifying high-basis lots reduces the taxable gain, which the average obscures.
A worked example
Take the 100@$50 + 50@$30 scenario. These figures are produced by the calculator above, not written alongside it, so they always match what the tool returns.
What you enter
- First buy — shares
- 100
- First buy — price per share
- $50
- Second buy — shares
- 50
- Second buy — price per share
- $30
What it returns
- Average cost per share
- $43.33
- Total shares
- 150
- Total invested
- $6,500
- Break-even price
- $43.33
Sources
This calculator uses no external data — the result follows entirely from the formula above and the values you enter, so there is nothing to cite beyond the arithmetic.
Calculator last reviewed August 9, 2026. How we verify
Try an example
Frequently asked questions
How do I calculate my average stock cost?
Add up the total amount you paid across all purchases, then divide by the total number of shares. Buying 100 shares at $50 ($5,000) and 50 at $30 ($1,500) is $6,500 for 150 shares — an average cost of about $43.33 per share. This becomes your break-even price.
What is 'averaging down'?
Buying more shares of a stock after its price has fallen, which lowers your average cost per share. It reduces the price you need to break even, but it also increases your position in a losing investment — so it only pays off if the stock recovers. Averaging down on a declining company can deepen losses.
What is cost basis and why does it matter?
Cost basis is the total amount you paid for an investment, including any fees — the figure used to calculate your capital gain or loss when you sell. A lower average cost basis means a larger taxable gain (or smaller loss). Brokerages track it for you, but it's worth understanding for tax planning.
Should I average down or cut my losses?
It depends on why the price fell. If your original reason to own the stock still holds and the drop is temporary, averaging down can be sound. If the company's fundamentals have deteriorated, adding more money often just increases the loss — the classic 'throwing good money after bad.' Judge the business, not just the price.
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Disclaimer: DayCents provides this calculator for educational purposes only. Results are estimates based on your inputs and the stated assumptions — they are not financial advice, a quote, or an offer of credit. Consult a qualified financial professional before making major money decisions.