What is a stock average cost calculator?

It computes your weighted average cost basis across multiple buys. If you bought 50 shares at $100 and 50 at $80, your average cost is $90 — not a simple midpoint of the prices unless share counts match.

How do you calculate average cost of stocks?

Average cost = Total dollars invested ÷ Total shares. Example: ($100×50) + ($80×50) = $9,000 ÷ 100 shares = $90 per share.

What does averaging down mean?

Averaging down means buying more shares after the price falls so your average cost drops. It can reduce break-even — or increase losses if the thesis was wrong. Never average down just to feel better about a red position.

Is average cost the same as break-even?

Before fees and taxes, yes — you need the stock above average cost to show an unrealized gain. Fees, dividends, and taxes can shift the true economic break-even. Use a stock profit calculator when you model an exit.

Is this average cost calculator free?

Yes — free, no signup. Add as many purchase lots as you need and optionally mark the current price for unrealized P&L.

All tools

Average Cost Calculator

Free stock average cost calculator. Combine multiple buys to get weighted average cost basis, total invested, and P&L — built for averaging down and cost-basis tracking.

Add buys at different prices (or model averaging down) and get weighted average cost, total shares, total invested, and unrealized P&L at a mark price. The answer to “what’s my breakeven after that add?”

Purchase lots

Currency

Current / mark price ($)

Lot 1 shares

Price ($)

Lot 2 shares

Price ($)

Tip: model an average-down by adding a second lot at a lower price and watching average cost fall.

Average cost

Avg cost / share

$90.00

Your break-even before fees/taxes

Total shares: 100
Total invested: $9,000.00
Market value: $9,000.00
Unrealized P&L: +$0.00 (0%)

What is an average cost calculator?

An average cost calculator (or stock cost basis calculator) tells you the true price you paid per share after several buys. Brokers show this as cost basis; traders use it to know break-even after averaging down or scaling in. Without it, people guess — and guess wrong when lot sizes differ.

Average cost formula

Average cost = Σ (shares × price) ÷ Σ shares

Example: 40 shares at $50 ($2,000) + 60 shares at $40 ($2,400) = $4,400 total ÷ 100 shares = $44 average cost. A simple average of $50 and $40 ($45) would be wrong because the lots aren't equal size.

How to use this free stock average calculator

Enter each purchase as its own lot (shares + price).
Click “Add another buy” to model an average-down or scale-in.
Set the current / mark price to see unrealized P&L vs average cost.
Planning the exit? Use the stock profit calculator with your average cost as the buy price.

Averaging down: when it helps vs hurts

Averaging down lowers break-even if the business thesis is still intact and you sized the adds with risk rules. It hurts when you're throwing good money after a broken thesis, or when the add is so large that one name dominates the portfolio. A calculator shows the math — it doesn't make the decision for you.

Size any add with the position size calculator so “buying the dip” doesn't silently double your account risk.

Average cost vs DCA

Dollar-cost averaging is a schedule (invest fixed amounts over time). Average cost is the resulting number. Our DCA calculator projects a contribution plan; this average cost tool reconstructs basis from specific lots you already bought (or plan to buy).

Deeper walkthrough: average cost basis explained.

Frequently asked questions

Related free trading tools

Explore more free calculators and simulators on Swift Penguin: stock market simulator, live stock lookup, position size calculator, risk reward calculator, compound growth projector, dividend & DRIP calculator, options profit calculator, portfolio tracker, dollar cost averaging calculator, stock profit calculator, investment return calculator, and capital gains tax calculator. Browse all free stock trading tools.

Educational calculator only — not tax or investment advice. Broker cost basis methods (FIFO, specific ID) can differ for tax lots.

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Related guides

Tools7 min read

Average Cost Basis Explained (And How Averaging Down Works)

How weighted average cost basis is calculated for stocks, when averaging down helps, and how to find your break-even price.

Understand weighted average cost, work a multi-lot example, and see when averaging down is strategy vs coping. Use our free average cost calculator for the math.

Read guide