This stock average calculator finds your true average cost per share when you have bought a stock at different prices — whether you dollar-cost averaged in on the way up or averaged down after a dip. Enter each buy’s share count and price, and it returns your weighted average cost, total position size, and (optionally) your unrealized profit or loss at today’s price.
The key word is weighted: buying 100 shares at $50 and 10 shares at $40 does not average to $45. The correct average is total dollars invested divided by total shares owned — the number this calculator computes and the price your position must return to for you to break even.
The Weighted Average Formula
Average cost per share = total cost ÷ total shares:
average = (shares₁ × price₁ + shares₂ × price₂ + …) ÷ (shares₁ + shares₂ + …)
Example — averaging down:
- Buy 1: 100 shares at $50 = $5,000
- Buy 2: 100 shares at $40 = $4,000
- Total: 200 shares for $9,000 → average cost $45.00
The stock no longer needs to recover to $50 for you to break even — only to $45. At a current price of $42, the position is worth $8,400 against $9,000 invested: an unrealized loss of $600, or −6.67%.
Averaging Down: The Math and the Risk
Averaging down lowers your break-even, but the leverage is weaker than intuition suggests: equal-sized buys move your average only halfway toward the new price, and each successive buy moves it less because the denominator grows.
The risk side deserves equal weight. Averaging down concentrates more capital in a position that is falling — which is only wise if the original investment thesis still holds and the decline is market noise rather than deteriorating fundamentals. “It’s cheaper now” is a fact about your entry price, not about the company. Dollar-cost averaging on a schedule (buying fixed amounts at fixed intervals, regardless of price) achieves the averaging benefit without the temptation to throw good money after a broken thesis.
Cost Basis vs. Your Average — the Tax Wrinkle
Your average cost is the right number for judging the position’s performance, but taxes work on individual lots:
- FIFO (first in, first out): the default at most US brokers — selling 100 of your 200 shares sells the $50 lot first, realizing a bigger loss (or smaller gain)
- Specific-lot identification: you choose which lot to sell, controlling the realized gain or loss
- Average cost method: applies to mutual funds and some DRIP plans, not typically to individual stocks
Holding period also attaches per lot — shares held over a year get long-term capital-gains treatment. If you plan to sell only part of a multi-lot position, the lot you designate can change your tax bill meaningfully.
Frequently Asked Questions
How do I calculate my average stock price after buying twice?
Add up the total dollars spent across both buys, then divide by total shares. For 100 shares at $50 plus 100 shares at $40: $9,000 ÷ 200 shares = $45 average. Never average the prices alone unless the share counts are identical.
Does averaging down work?
Mathematically it always lowers your break-even price. Whether it is a good idea depends on why the stock fell: averaging down into temporary weakness in a sound company reduces your recovery hurdle, while averaging down into deteriorating fundamentals concentrates losses. The calculator gives you the math; the judgment about the business is yours.
What price do I need to break even?
Exactly your average cost per share — the highlighted result above. If you own 200 shares at a $45 average, the position breaks even when the stock trades at $45 (before commissions and taxes). Anything above that is unrealized gain.
Is my average cost the same as my cost basis for taxes?
Not necessarily. Your average tells you position-level performance, but the IRS taxes individual lots, and most brokers default to FIFO when you sell partially. If tax outcome matters, use your broker’s specific-lot selection at the time of sale rather than assuming the average applies.
How is this different from dollar-cost averaging?
Same math, different behavior. Dollar-cost averaging is a schedule — investing a fixed amount at regular intervals regardless of price, which automatically buys more shares when prices are low. Averaging down is a discretionary decision to add to a losing position. Both produce a weighted average cost, which this calculator computes for any combination of buys.