How it works
Cost = buy amount × (1 + buy fee). Proceeds = sell amount × (1 − sell fee − tax). Net profit = proceeds − cost, and return = net profit ÷ cost.
Break-even price
Break-even sell price = buy price × (1 + buy fee) ÷ (1 − sell fee − tax). You need to sell above it to make money after costs.
About the defaults
The 0.015% fee and 0.20% tax are examples based on typical Korean brokerage accounts. Transaction tax rates change by market and year, so use your actual rates.