Stock Average Calculator

Averaging down means buying more of a stock you already own at a lower price so your average cost per share drops. This stock average calculator (평단가 계산기) works out the weighted average price: it multiplies each buy's shares by its price, adds those amounts to get your total cost, then divides by your total shares. Because it is share-weighted, a large buy moves your average more than a small one — which is exactly why adding shares at a lower price pulls your average down.

Break-even is the sell price at which your proceeds after costs equal what you paid. This break even price calculator takes your total buy cost (including any buy fee), then divides by your shares times one-minus-sell-costs, where sell costs are the sell fee plus transaction tax. Fees and tax are money you never get back, so you must sell a little higher than your average just to reach zero. The Korea preset uses a 0.15% securities transaction tax — the effective KOSPI/KOSDAQ rate after the 2025 reform (0% base securities tax plus 0.15% special rural tax, per Korea's Securities Transaction Tax Act); it applies to sells only and defaults to 0.

Use the averaging-down planner (물타기 계산기). Enter your current price and a target average that sits between the current price and your existing average, and it solves for the shares to buy: shares = your shares × (average − target) ÷ (target − current price). It also shows the cash that buy would cost. If your target is above your current average or below the current price it is not reachable by buying more, so the tool tells you instead of returning a misleading number.

Yes. Pick your currency and every amount is formatted with your locale's grouping, symbol and decimal places (KRW and JPY show no decimals, USD and EUR show two) — nothing is hard-coded, so it works as an average down calculator in dollars, won or anything else. Prices and break-even show extra decimals for low-priced shares. Share quantities accept decimals up to four places, so partial shares and ETF fractional positions are handled the same way as whole shares.

No data leaves your device. Every calculation — the weighted average share price, break-even and cost basis — runs entirely in your browser with no login, no account and no prices fetched from any market feed; you type every price yourself. Your last entry is saved only in your browser's local storage so it is there when you return. And this is arithmetic, not investment advice: it tells you the math of your cost basis, not whether to buy, hold or sell.