Stock Profit Calculator: Why Break-Even Isn't Your Buy Price

The gap between gross profit and what you actually keep

The naive way to think about a trade's profit is sell price minus buy price, times shares. That number — gross profit — is real, but it's not what you actually pocket. Every trade typically involves two commission charges: one when you bought the shares, one when you sell them. Both come out of your actual return regardless of which direction the trade went, which means the breakeven point for a trade with commissions is never exactly your buy price — it's always somewhat higher, because you need the sale to cover both fees before you're truly ahead.

This is the core distinction this tool is built around: gross profit tells you how the stock price moved, net profit tells you what you actually made after the real cost of executing both sides of the trade.

The four numbers, and how they relate

Running the numbers on your trade

Enter the buy price per share and the number of shares.

Enter the sell price per share — or leave it blank to see the break-even price instead.

Optionally add per-trade commissions for both the buy and sell legs.

Read the gross profit, net profit, ROI percentage, and break-even sell price.

Why total cost, not just the share cost, drives ROI

ROI here is net profit divided by total cost, and total cost specifically includes the buy commission, not just buy price × shares. This matters because it means ROI reflects your actual out-of-pocket investment, not just the market value of what you bought. Two trades with identical share prices and identical price movement can have slightly different ROI if their commission structures differ — a lower-commission broker doesn't just save you money in absolute terms, it also makes your total cost basis smaller, which mechanically produces a higher ROI percentage for the same underlying gain.

Why break-even sits above your buy price, and by how much

This is exactly why the break-even figure is worth checking before assuming a small price bump means you're in profit — on a small trade with meaningful flat commissions, the stock may need to move further than intuition suggests just to cover the round-trip cost of entering and exiting.

Fractional shares work the same way, just with decimals

Every formula here works identically whether shares is a whole number or a decimal like 0.5 or 12.75, since the math is purely multiplicative and divisive with no assumption of whole-share lots. This matters more than it might seem: fractional trading has become standard at most modern brokers, and a break-even calculation on a fractional position follows exactly the same total-commission-divided-by-shares logic as a whole-share position — the commission drag per share simply spreads across however many fractional shares you actually hold.

Common mistakes

Assuming break-even equals your buy price — with any commissions involved, break-even is always somewhat above buy price, and the gap shrinks as trade size grows.

Comparing gross profit across trades with different commission structures as if it reflects real return — gross profit ignores fees entirely; net profit and ROI are the numbers that account for them.

Forgetting that taxes aren't included in any of these figures — net profit here is pre-tax, and actual after-tax proceeds will be lower.

Treating a small percentage price gain as automatic profit on a small trade with flat commissions — check the break-even price specifically, since commission drag hits small trades hardest.

Real use cases

Checking whether a modest price gain on a trade actually covers both commission legs before deciding whether to sell.

Comparing the effective cost of two different broker commission structures on the same hypothetical trade.

Working out the ROI on a completed trade for personal record-keeping or performance tracking.

Estimating what sell price is needed to hit a specific target profit, by testing sell prices against the net profit output.

Frequently asked questions

Q: How is ROI calculated?

A: ROI = (net profit ÷ total cost) × 100. Total cost includes the buy commission, and net profit subtracts both commissions from the gross gain.

Q: What's the break-even price?

A: The sell price at which net profit is exactly zero — (buy price × shares + buy commission + sell commission) ÷ shares. Above this price you profit; below it you lose.

Q: Does this account for taxes?

A: No. Use the Crypto Tax Calculator (works for stocks too) for after-tax returns, or multiply your net profit by (1 − tax rate) for a quick estimate.

Q: Can I model fractional shares?

A: Yes. Enter any positive decimal for shares, such as 0.5 or 12.75 — most modern brokers support fractional trading, and the math scales the same way regardless.

Q: What about dividend reinvestment?

A: Not modeled here. Treat reinvested dividends as additional buys at the dividend date, or use the Dividend Yield Calculator to project forward dividend income separately.

Q: Are my trades uploaded?

A: No. The math runs entirely in your browser.

Q: Why does the same dollar amount of commission hurt a small trade more than a large one?

A: Because break-even's commission impact is total commissions divided by number of shares — a fixed dollar commission spread across fewer shares adds more to the per-share break-even price than the same commission spread across many shares.

Run the numbers on your trade

Calculate your real return with the Stock Profit Calculator. Estimating after-tax proceeds? Try the Crypto Tax Calculator. Projecting future dividend income or long-term growth instead? Check the Dividend Yield Calculator and Investment Growth Calculator.