Stock Averaging Down Calculator

Enter your current shares, average cost, and current price to see your new average cost after buying more, and the return you'd need from here to break even. If you haven't decided how many shares to buy, switch to "Work backward from a target average" to solve for the shares needed to hit a specific average price. Works for both KRW (domestic Korean stocks) and USD (overseas stocks) — just switch the currency.

Currency KRW (₩) — domestic Korean stock USD ($) — overseas stock

Current shares held Current average cost Current price The price you're assuming for the additional purchase.

Calculation mode Enter shares to buy Work backward from a target average

Additional shares to buy Brokerage commission rate (%) Assumed the same for buying and selling — this varies by broker, so swap in your actual rate for an accurate result. Reference — typical online rates: Korea's Kiwoom Securities (Yeongungmun) charges 0.015%, and Toss Securities charges 0.015% (0.014% on NXT-matched trades). Many brokers also run temporary 0% promotions for new accounts, so check your own account's actual rate.

Current loss -

- -

Loss after buying more -

Return needed after -

"Loss" is simply how far below (or above) your average cost the current price is. "Return needed" goes further and accounts for commission and tax — how much further the price actually has to rise from here to reach true breakeven. The two aren't the same number, because a drop and the rally that undoes it aren't symmetric (e.g. a 20% drop needs a 25% rally to recover).

Purchase breakdown
Existing position (reference only) = existing shares × existing average cost -	-

Additional shares to buy - -	-
Cost of additional shares = additional shares × current price -	-
Total shares held = existing shares + additional shares -	-
Total invested = existing position value + cost of additional shares -	-
New average cost = total invested ÷ total shares held -	-
Breakeven price before (incl. transaction costs) = existing average ÷ (1 − commission×2 − transaction tax) -	-
Breakeven price after (incl. transaction costs) = new average ÷ (1 − commission×2 − transaction tax) -	-

If the price keeps falling (assumes you keep buying the same number of shares each round)
vs. current price	Buy price	Cumulative average	Cumulative invested	Return needed

This result is a simplified estimate. For domestic Korean stocks (KRW), the securities transaction tax on selling (0.20% on both KOSPI and KOSDAQ, including the agricultural/fishing surtax, under the rate effective 2026-01-01) is applied automatically. For overseas stocks (USD), Korea's annual capital gains tax on foreign stock trading (22–27.5% on net gains over 2.5M KRW/year, aggregated across all your foreign-stock trades for the year) is not included — that's an annual, portfolio-wide tax, which doesn't fit the scope of a single-position averaging tool. Swap in your actual broker's commission rate. The simulation assumes you buy the same number of shares each round — whether to keep averaging down (or cut your losses) should depend on the stock's fundamentals and your own capital, not just this arithmetic.

Frequently Asked Questions

I entered a target average and it says "not achievable" — why?

Your average cost is always a value between your existing average and the price you're buying at (the current price) — by the nature of a weighted average, buying more shares at the current price only pulls your average closer to the current price, never past it or equal to it (you'd need infinite shares to even get arbitrarily close). For example, if your existing average is 150 and the current price is 100, entering a target of 90 is impossible no matter how many shares you buy — so it's marked "not achievable." Enter a target that's higher than the current price and lower than your existing average.

Why is the breakeven price different from the average cost?

Selling at exactly your average cost is actually a loss once you account for transaction costs (commission on both the buy and the sell, plus securities transaction tax on the sell for domestic stocks). So the price that's truly "breakeven" is a bit higher than your raw average — this calculator shows that separately as the "breakeven price." The formula is average cost ÷ (1 − commission×2 − transaction tax rate) (commission applies twice — buy and sell — while the tax applies once, on the sell).

Why does the transaction tax only apply to KRW (domestic stocks)?

Every sale of a domestic Korean stock automatically incurs a securities transaction tax (0.20% on both KOSPI and KOSDAQ, including the agricultural/fishing surtax, under the rate effective 2026-01-01). Overseas stocks have no Korean-side sell tax, but instead have an annual capital gains tax (22–27.5% on net gains over 2.5M KRW per year) that's assessed on your entire year's foreign-stock trading, not a single position. That's out of scope for a tool that calculates one position's averaging (it would need your full year of trades to compute) — keep this in mind when working in USD.

What does the simulation table show?

It shows what happens if you don't stop at one round of averaging down — if the price keeps falling and you keep buying the same number of shares each time. Your average cost keeps dropping, but so does the capital required — which is the real risk of averaging down that a single calculation hides. Whether you'd actually have the capital to keep buying, and whether the stock is even worth holding that long, are separate judgment calls this table doesn't make for you.

Why do I have to enter the brokerage commission rate myself?

Unlike the securities transaction tax, commission isn't set by law — it's whatever your broker charges. Many online no-fee accounts are close to 0%, while full-service branch trading can be much higher. Enter your actual broker's rate for an accurate result.