Stock Average Down Calculator
Enter each purchase to see your average cost per share, test a new buy before you place it, and check your break-even price and unrealized profit.
Average cost per share
45.00
Total shares
200
Total invested
9,000.00
Break-even price: 45.00 per share (before fees)
What if I buy more?
For information only, not investment advice. Figures exclude fees and taxes. Calculated on your device; nothing is sent anywhere.
How it works
- Add a row for each purchase with the number of shares and the price you paid per share — the average cost updates as you type.
- Use the what-if row to enter a hypothetical new buy and instantly see how it would change your average cost per share.
- Enter the current market price to see your break-even level and your unrealized profit or loss in dollars and percent.
Frequently asked questions
- How is the average cost per share calculated?
- The calculator multiplies shares by price for every row to get the total amount invested, then divides that total by the total number of shares. This weighted average is the standard cost-basis method most brokers display, so your result should match your brokerage statement before fees.
- What does averaging down actually do to my position?
- Buying more shares at a lower price pulls your average cost down toward the new purchase price, which lowers the price the stock must recover to for you to break even. It also increases the total capital at risk, so the what-if row shows both the new average and the new total invested before you commit.
- Does the break-even price include trading fees or taxes?
- No. The break-even shown equals your average cost per share and ignores commissions, exchange fees, and taxes. If your broker charges per-trade fees, your true break-even is slightly higher — you can approximate it by adding the fee divided by your share count to the average.
- Is my portfolio data uploaded anywhere?
- No. Every calculation runs locally in your browser using plain JavaScript, and nothing you type is sent to a server or stored after you leave the page. That makes it safe to enter real position sizes without exposing your holdings.
- Can I use this for crypto, ETFs, or fractional shares?
- Yes. The math is identical for any asset bought in multiple lots — stocks, ETFs, crypto, or funds. Fractional quantities work too: enter 2.5 shares or 0.014 BTC and the weighted average is computed the same way.
About this tool
This stock average calculator works out the weighted average cost per share of a position built over multiple purchases. Each buy row takes a share count and a price per share; the tool sums the invested amounts, divides by the total shares, and shows your average cost, total shares, and total invested. Because the average is weighted by position size, a large lot moves it far more than a small one — which is exactly what a simple average of the prices would get wrong.
Everything runs client-side in your browser. There is no upload, no account, and no stored data: the numbers exist only on your screen while the page is open. The results update live as you type, so you can adjust a share count or price and watch the average, break-even line, and profit figures recalculate immediately.
The what-if row is the part most traders use before placing an order. Enter a hypothetical purchase — say 100 more shares at today’s price — and the calculator shows the new average cost next to your current one, along with the new total invested. This makes the trade-off of averaging down concrete: you can see precisely how far the extra capital pulls your break-even price down before you commit real money. Adding the current market price completes the picture with your unrealized profit or loss in both dollars and percent.
A few practical tips: enter buys in any order, since a weighted average does not depend on sequence; use fractional share counts freely if your broker supports them; and remember that the break-even shown excludes commissions and taxes, so treat it as a floor rather than an exact target. The same math applies to ETFs, crypto, and any asset accumulated in lots.