Stock Average Calculator

Your true average cost across every purchase, your position’s profit or loss at any price — and the exact number of shares to buy to hit a target average.

Your purchases

Add every buy — shares and the price you paid. Fractional shares are fine.

SharesPrice per share
🎯 Average down to a target

Average cost per share

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Total shares—
Total invested—
Purchases—

How it’s calculated

Average cost = total money invested ÷ total shares = Σ(shares × price) ÷ Σ shares
Shares to reach target T buying at price P = current shares × (average − T) ÷ (T − P). The target must sit between your current average and the buy price.

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Why average cost is the number that matters

Once you’ve bought a stock more than once, no single purchase price describes your position — your average cost does. It’s a weighted average: total money in divided by total shares held, so bigger lots pull the average toward their price. Every meaningful question about the position — am I up or down, where’s my break-even, should I add more — is answered relative to this one number, and this calculator keeps it exact across as many buys as you’ve made, fractional shares included.

Averaging down, with the guesswork removed

When a stock falls below your average, buying more lowers that average — but most people guess at how much to buy. The target solver inverts the formula: tell it the average you want and the price available now, and it returns the exact share count (and cash outlay) required. Two cautions worth taking seriously: the target must lie between the current price and your existing average (you can’t average down to a number below what shares cost today), and averaging down concentrates more money in a falling position — it lowers your break-even, not the risk. Make sure the reason you’d buy today stands on its own.

From average cost to profit

Enter the current market price and the calculator marks your whole position to market: total value and unrealized gain or loss versus everything you’ve invested. When you eventually sell, run the exit through the stock profit calculator to fold in commissions and dividends, or check what a disciplined monthly plan would build with the investment growth calculator.

Frequently asked questions

How do you calculate average stock price after multiple buys?
Add up the total spent across all purchases (each lot’s shares × price), then divide by the total number of shares. Buying 100 shares at $20 and 50 at $25 costs $3,250 for 150 shares — an average of $21.67.
How many shares do I need to buy to average down to a target?
Shares needed = current shares × (current average − target) ÷ (target − buy price). With 150 shares at a $21.67 average, reaching a $21 average buying at $18 takes 33.3 more shares. The target must sit between today’s price and your current average.
Is averaging down a good idea?
It cuts your break-even, but it also puts more money into a position that’s falling — sometimes for good reason. It works best when you’d happily buy the stock today on its own merits; it works worst as a way to avoid admitting a mistake.
Does averaging up work the same way?
Yes — buying above your average raises it, and the same formulas apply in reverse. Many traders deliberately average up into positions that are working, accepting a higher break-even for a larger stake.
Should I include commissions in my average cost?
For precision, yes — add each buy’s fee into that lot’s cost (or bump the price slightly). With commission-free brokers the difference is usually negligible, which is why the calculator keeps lots to shares × price.
Is this the same as the cost basis used for taxes?
Average cost is one accounting method, and it’s standard for mutual funds. For individual stocks, US brokers typically default to FIFO (first-in-first-out) for taxes unless you specify lots — so your taxable basis on a partial sale may differ from your average.
Does this work for crypto too?
The math is identical — total spent ÷ total units. Fractional quantities are supported, so you can enter 0.0155 BTC the same way as 100 shares. For a full buy/sell profit picture with exchange fees, use the crypto profit calculator.

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