— Stock Market
Stock Average Calculator
Find your weighted-average cost after buying a stock at different prices. Add each purchase price and quantity to see average cost, total shares, total invested, unrealized profit or loss, and shares needed to reach a target average.
Average buy price
$90
- Total shares
- 20
- Total invested
- $1,800
Try: Average two buys (100 & 80), Unrealized P/L at 85, Average down to a 88 target, Three lots with charges
— Each purchase & running average
| Lot | Price | Qty | Cost | Running avg |
|---|---|---|---|---|
| 1 | $100 | 10 | $1,000 | $100 |
| 2 | $80 | 10 | $800 | $90 |
— Average price across purchases
Download— How it works
Average = Σ(price × quantity) ÷ Σ(quantity), optionally including per-lot charges. To hit a target average, the shares to buy at the current price = (target × shares − invested) ÷ (current price − target).
What averaging really gives you
When you buy the same stock at different prices, your average cost is the weighted average — each price counts in proportion to how many shares you bought at it, not a simple midpoint. Total up price × quantity for every lot and divide by your total shares. That single number is your breakeven: above it you’re in profit, below it you’re down. The running-average column shows how each purchase nudges it, and the chart traces the same path.
Worked example — 10 shares at 100, then 10 at 80: Total invested = 1,000 + 800 = 1,800 over 20 shares, so the average is 1,800 ÷ 20 = 90 — not 90 by luck of equal sizes, but the weighted result. Buy unequal amounts and it tilts toward the price you bought more of.
Averaging down to a target
Averaging down means buying more after the price has fallen, to pull your average closer to the current price. Set a target average and the current price, and the calculator solves exactly how many shares to buy to hit it — and what that costs. The catch: you can only lower your average toward the price you’re buying at, never below it, so a target beneath the current price is impossible (the tool flags it). Averaging down adds to a losing position, which deepens your exposure if it keeps falling — size it deliberately.
Charges, sells and the caveat
Turn on per-purchase charges to fold brokerage and fees into your true average cost — the price-only figure is shown alongside for comparison. Selling part of your holding doesn’t change your average cost per remaining share; you just hold fewer, so the tool shows the remaining shares and cost basis at the same average. This is arithmetic on the numbers you enter, not investment advice — and a lower average never guarantees a profit if the stock keeps sliding.
— Reader questions
How do I calculate my average share price?
Multiply each purchase’s price by its quantity, add them up, and divide by your total shares. Buying 10 at 100 and 10 at 80 gives (1,000 + 800) ÷ 20 = an average of 90.
What is averaging down?
Buying more shares after the price has dropped, which lowers your average cost toward the current price. It reduces your breakeven but increases your stake in a falling stock — use it deliberately, not reflexively.
How many shares should I buy to reach a target average?
Enter a target average and the current price; the calculator solves it: shares to buy = (target × current shares − total invested) ÷ (current price − target). It only works when the target is between the current price and your existing average.
Does selling change my average cost?
No. Selling some shares leaves your average cost per remaining share unchanged — you simply hold fewer. Your average only moves when you buy at a different price.
Should I include brokerage in the average?
For a true cost basis, yes — turn on per-purchase charges and the calculator adds them, since fees raise what each share actually cost you. It shows the price-only average too for reference.