Calculating Stock Returns with Entered Commissions and Transaction Tax
A simple valuation gain can differ from the amount settled after a sale. This calculator estimates one trade using only the buy/sell commission and sell-side transaction-tax rates you enter. It does not calculate dividend or capital-gains tax, FX effects, exchange/clearing charges, bid-ask spread, or market impact, so do not read the result as total after-tax return or exact settlement proceeds. Confirm current rates for the market, product, broker, account, and trade date before entering them.
Headline Return vs. Entered-Cost-Adjusted Return
Simple (headline) return is (sell price − buy price) ÷ buy price. This calculator's cost-adjusted return subtracts the entered two-way commissions and sell-side transaction tax from profit relative to the purchase amount. Its scope is narrower than a legal or tax-accounting measure of realized return that includes every applicable cost and tax. With unchanged rates, repeated trades can accumulate repeated costs.
- Buying costs: this calculator applies the brokerage commission you enter to the purchase amount. Check the account terms for the actual rate, minimum fee, and exchange/clearing charges.
- Selling costs: brokerage commission + securities transaction tax (charged only on sales).
- While holding: ordinary Korean dividends paid to a resident are generally subject to 15.4% withholding, but the result can vary with dividend type, residency, and aggregate financial income. This calculator excludes dividend tax.
Korean Stock Taxes and Transaction Rates for 2026
The key point about securities transaction tax is that it applies to the full sale amount regardless of whether you made a profit. You pay it even when you sell at a loss. The 2026 rates by market are as follows.
| Category | 2026 Rate | Notes |
|---|---|---|
| KOSPI (transaction + rural tax) | 0.20% (0.05% tax + 0.15% rural special tax) | On sale |
| KOSDAQ | 0.20% | No rural special tax |
| Dividend tax | 15.4% (14% income + 1.4% local) | Withheld; comprehensive taxation if annual financial income exceeds 20M KRW |
| General large-shareholder capital-gains rate (tax base ≤300M) | 22% | Local tax included; separate rates can apply to certain short-held shares |
| General large-shareholder capital-gains rate (portion above a 300M tax base) | 27.5% | Local tax included; separate rates can apply to certain short-held shares |
A Korean-resident individual who is not a large shareholder is generally outside capital-gains taxation when transferring domestic listed shares on an exchange, but off-exchange and unlisted-share transfers can differ. Listed-share large-shareholder status includes a KRW 5 billion per-stock market-value test or ownership-ratio tests at the end of the preceding business year (KOSPI 1%, KOSDAQ 2%, KONEX 4%); acquiring enough shares later to meet a ratio can also trigger the rule. Related-party aggregation can vary when the person is part of the largest-shareholder group, so personal account value or a simple year-end sale does not settle the classification. General rates are 20% up to a KRW 300 million tax base and 25% on the excess, before local income tax, but SME status and certain holdings under one year can invoke different rates. This calculator determines neither status nor capital-gains tax; check the NTS guidance for the relevant transfer period.
Worked Example — Short-Term KOSPI Trade
For a calculation-only example, assume you buy at 1,000,000 KRW and sell at 1,050,000 KRW, entering a 0.015% commission both ways and a 0.20% sell-side transaction tax. These are hypothetical inputs, not a current quote for every broker or trade.
- Buy commission: 1,000,000 × 0.015% = 150 KRW, total cost basis 1,000,150 KRW
- Sell commission: 1,050,000 × 0.015% = 157 KRW
- Transaction tax: 1,050,000 × 0.20% = 2,100 KRW
- Net proceeds: 1,050,000 − 157 − 2,100 = 1,047,743 KRW
- Modeled net profit after the entered costs: 1,047,743 − 1,000,150 = 47,593 KRW → calculator return about 4.76%
In this single-trade example, the +5.0% headline return becomes about 4.76% after the entered costs. Repeated trades repeat costs, but the annual return effect depends on trade size, price changes, and reinvestment, so it cannot be found by simply multiplying this gap by the trade count. The calculator's break-even price likewise reflects only the entered commission and transaction tax.
Overseas Stocks and Common Average-Price Mistakes
For Korean tax residents, gains on overseas shares can fall under a different capital-gains regime from exchange-traded domestic shares held by small shareholders. Confirm the annual deduction, permitted gain/loss netting, filing deadline, and tax conversion rates for the relevant year. This calculator does not calculate overseas-share capital-gains tax or FX gain/loss; residency, source-country withholding, and the scope of domestic/foreign netting can also change the result.
- Average-price illusion: even if averaging down lowers your average price, the rebound needed to recover is larger than the loss. A −20% loss needs +25% to break even.
- Splitting sale dates: different tax years may change deduction use, but price movement, FX, and transaction costs can outweigh the tax effect. Do not time a sale from the deduction alone.
- Ignoring FX gains/losses: won-denominated taxable gain depends on the prescribed conversion method and rates. Do not calculate a filing amount from the dollar screen return alone.
- Use the stock return calculator to estimate one trade after the commission and transaction-tax rates you enter.
- To compare dividends with deposit interest, the interest calculator helps.
- When converting overseas sale proceeds to won, use the exchange rate calculator alongside it.