Why is my return lower here than on my brokerage app?

Because the two are usually measuring different things. Many app screens show the gross move between your average cost and the current or sold price, with costs excluded or applied only on one side. This calculator applies commission on the buy and the sell, then subtracts the transaction tax, and divides by what you actually put in — buy amount plus buy commission — rather than by the buy amount alone. Each of those choices moves the figure down slightly, and together they explain most of the gap. If the difference is larger than a fraction of a percent, the likely cause is the commission rate: the default here is a common retail figure, not your rate.

What exactly is the break-even sell price?

It is the sell price at which the cash you receive exactly equals the cash you put in — the point where the trade neither makes nor loses money. It always sits above your buy price, because you pay commission twice and the transaction tax once, and all of those have to be earned back before the first won of profit. That gap is the reason a stock can be up on the day and still lose you money if you sell. The card shows the price and, underneath it, how far above your buy price it sits as a percentage.

Which commission rate should I enter?

Yours, not the default. Korean brokerage commission varies by firm, by whether you trade through the app or a branch, and above all by the promotion the account was opened under — some non-face-to-face accounts pay a rate close to zero for a fixed period, while a branch-opened account can pay many times more. The reliable way to find it is to open a past contract note or transaction history entry and read the commission line against the trade amount. The default here is a common retail figure included so the calculator returns something sensible before you change it.

Is the transaction tax rate in this calculator current?

Treat it as a starting value, not an authority. The rate is set by law and has been revised more than once in recent years, so any figure written into a calculator drifts out of date between revisions. That is precisely why the field is editable rather than fixed. Before relying on the tax line, check the current rate — your brokerage's fee schedule states it, and it appears on every contract note for a sale. The tax applies to the sale side only, and only to domestic shares.

Can I use this for overseas shares?

For the return itself, yes — untick the transaction tax, since overseas shares are not taxed per trade. But do not read the result as your tax position. Korean tax on overseas shares works on the whole year at once: every sale is netted together, a single annual deduction is applied, and what remains is taxed once. A per-trade figure cannot express that, and it also ignores the exchange rate, which changes the won value of a gain even when the share price did not move. Use a dedicated overseas capital gains calculator for the tax.

I sold only part of my position. Does that work?

Yes. Enter the quantity you actually sold and the calculator prices that sale on its own, apportioning the buy cost to the shares that left. The shares you still hold are excluded on purpose: nothing has been realised on them, so including them would blend a booked result with a paper one and make the return mean two things at once. If you want the unrealised side too, run the calculator a second time with the current price as the sell price — that gives you what the rest is worth today, kept separate.

Why does the annualised return look so extreme?

Because annualising asks what rate would produce your result if it repeated for a whole year, and a short holding period makes that hypothetical enormous. Gaining 3% in ten days annualises to a figure well into three digits — not because the trade was exceptional, but because ten days is a small fraction of a year. It is a restatement, not a forecast, and it is most useful for comparing holdings of genuinely different lengths. Over very short periods, read the plain return instead.

What if I averaged down and don't know my average cost?

Your holdings screen shows it, but if you only have the individual fills you need to work it out first: total money spent across all the buys divided by total shares held. Do that before you come here, because this calculator asks for one buy price and treats it as the cost of every share you sold. An averaging-down calculator does the same arithmetic and also tells you what a further purchase would do to the average, which is a different question from what this tool answers.

Does this tool upload my data?

No. Everything runs right in your browser, so your data never leaves your device — it even works offline once the page has loaded. The last values you typed are remembered in your browser's own storage so the page is not blank when you return, and clearing your browser data removes them.

📈 Stock Return Calculator

The number on your trading screen is the gross move. What you actually keep is smaller, because commission is charged on both sides and Korea levies a transaction tax on the sale. Those costs are small individually and easy to ignore, but they set a floor: there is a sell price below which a trade loses money even though the share price went up. This calculator puts that floor on screen next to the return, so a small gain is never mistaken for a profit it is not.

A stock return calculator that prices a completed trade after costs: enter the buy price, the sell price and the quantity, and it returns the realised profit or loss, the percentage return, the sell price at which you would merely break even, and — if you supply the dates — the same result restated as an annual rate.

What you bought

Buy price per share (매수단가)

Shares bought (매수수량)

Buy date (optional)

What you sold

Sell price per share (매도단가)

Shares sold (매도수량)

Sell date (optional)

Fees and tax

Every field here is editable because none of these numbers is fixed. Brokerage rates differ per firm and change with sign-up events; the transaction tax is set by law and has been revised repeatedly.

Buy commission (%)

Sell commission (%)

Transaction tax on sale (%) — 2026 basis

Apply the transaction tax (domestic Korean shares). Uncheck for overseas shares — they are taxed on annual gains instead.

Return (수익률)

—

Realised profit or loss (실현손익)

—

Break-even sell price (본전 단가)

—

Where the money went

Read this before you rely on it

This is an estimate. Your brokerage's own contract note is the authority: it applies the commission tier and any event rate that actually attaches to your account, and rounds each line its own way. The transaction tax rate is set by law and has been changed several times in recent years — check the current rate before trusting the tax line.

Private by design. This tool runs entirely in your browser — nothing you enter is uploaded or stored, and it works offline.

About

The arithmetic is deliberately explicit rather than hidden behind one percentage. Your total invested is the buy amount plus the buy commission. What you receive is the sell amount minus the sell commission and minus the transaction tax. The difference between the two is the realised profit or loss, and the return is that difference over what you invested — not over the buy amount alone, which is the shortcut that quietly flatters every result.

The break-even price falls out of the same equation read backwards: it is the sell price at which what you receive exactly equals what you invested. Because costs scale with the sale, it always sits above your buy price, and the gap widens as commission and tax rise. Two accounts holding the same stock at the same average cost can therefore have different break-even prices.

Sell fewer shares than you bought and the calculator prices that partial sale only. The buy cost is apportioned to the shares that actually left; the shares you still hold are not valued, because nothing has been realised on them. The annualised figure is offered only when both dates are supplied, and it is a restatement rather than a projection — a 3% gain held for a fortnight annualises to a number that says more about the short holding period than about the position.

Every rate is an input rather than a constant. Brokerage commission differs by firm, by channel and by whatever promotion the account was opened under. The transaction tax is set by law and has been revised repeatedly in recent years. Baking either one in would produce a calculator that is quietly wrong a year later, so both are fields you can overwrite.

How to use

Enter what you bought — the price you actually paid per share and how many. If you built the position in several lots at different prices, use your average cost per share rather than any single fill; your holdings screen shows it. Every field carries a "?" that opens a plain-language note if you are unsure what belongs in it.
Enter what you sold. Selling fewer shares than you bought is fine — the calculator prices that partial sale on its own and apportions the buy cost to the shares that left, leaving the rest untouched.
Set the fees. Copy your commission rate off a past contract note rather than trusting the default, because it varies widely by firm and by how the account was opened. The transaction tax applies to the sale side only; confirm the current rate, since it is set by law and has changed several times.
If the stock is listed overseas, untick the transaction tax. Overseas shares are not taxed per trade — the gains are netted across the year and taxed once, which is a different calculation entirely.
Read the three cards. The return and the realised profit are the same result in two units; the third is the break-even sell price, the floor below which the trade loses money no matter what the chart did. Fill in both dates and a fourth panel restates the return as an annual rate.
Check the breakdown panel to see where the money actually went, including what share of the buy amount the costs consumed. Copy the whole thing to a clipboard with one button if you keep a trading journal.

FAQ

Why is my return lower here than on my brokerage app?: Because the two are usually measuring different things. Many app screens show the gross move between your average cost and the current or sold price, with costs excluded or applied only on one side. This calculator applies commission on the buy and the sell, then subtracts the transaction tax, and divides by what you actually put in — buy amount plus buy commission — rather than by the buy amount alone. Each of those choices moves the figure down slightly, and together they explain most of the gap. If the difference is larger than a fraction of a percent, the likely cause is the commission rate: the default here is a common retail figure, not your rate.
What exactly is the break-even sell price?: It is the sell price at which the cash you receive exactly equals the cash you put in — the point where the trade neither makes nor loses money. It always sits above your buy price, because you pay commission twice and the transaction tax once, and all of those have to be earned back before the first won of profit. That gap is the reason a stock can be up on the day and still lose you money if you sell. The card shows the price and, underneath it, how far above your buy price it sits as a percentage.
Which commission rate should I enter?: Yours, not the default. Korean brokerage commission varies by firm, by whether you trade through the app or a branch, and above all by the promotion the account was opened under — some non-face-to-face accounts pay a rate close to zero for a fixed period, while a branch-opened account can pay many times more. The reliable way to find it is to open a past contract note or transaction history entry and read the commission line against the trade amount. The default here is a common retail figure included so the calculator returns something sensible before you change it.
Is the transaction tax rate in this calculator current?: Treat it as a starting value, not an authority. The rate is set by law and has been revised more than once in recent years, so any figure written into a calculator drifts out of date between revisions. That is precisely why the field is editable rather than fixed. Before relying on the tax line, check the current rate — your brokerage's fee schedule states it, and it appears on every contract note for a sale. The tax applies to the sale side only, and only to domestic shares.
Can I use this for overseas shares?: For the return itself, yes — untick the transaction tax, since overseas shares are not taxed per trade. But do not read the result as your tax position. Korean tax on overseas shares works on the whole year at once: every sale is netted together, a single annual deduction is applied, and what remains is taxed once. A per-trade figure cannot express that, and it also ignores the exchange rate, which changes the won value of a gain even when the share price did not move. Use a dedicated overseas capital gains calculator for the tax.
I sold only part of my position. Does that work?: Yes. Enter the quantity you actually sold and the calculator prices that sale on its own, apportioning the buy cost to the shares that left. The shares you still hold are excluded on purpose: nothing has been realised on them, so including them would blend a booked result with a paper one and make the return mean two things at once. If you want the unrealised side too, run the calculator a second time with the current price as the sell price — that gives you what the rest is worth today, kept separate.
Why does the annualised return look so extreme?: Because annualising asks what rate would produce your result if it repeated for a whole year, and a short holding period makes that hypothetical enormous. Gaining 3% in ten days annualises to a figure well into three digits — not because the trade was exceptional, but because ten days is a small fraction of a year. It is a restatement, not a forecast, and it is most useful for comparing holdings of genuinely different lengths. Over very short periods, read the plain return instead.
What if I averaged down and don't know my average cost?: Your holdings screen shows it, but if you only have the individual fills you need to work it out first: total money spent across all the buys divided by total shares held. Do that before you come here, because this calculator asks for one buy price and treats it as the cost of every share you sold. An averaging-down calculator does the same arithmetic and also tells you what a further purchase would do to the average, which is a different question from what this tool answers.
Does this tool upload my data?: No. Everything runs right in your browser, so your data never leaves your device — it even works offline once the page has loaded. The last values you typed are remembered in your browser's own storage so the page is not blank when you return, and clearing your browser data removes them.