How the numbers are worked out
Profit is the sale proceeds minus what the position cost you minus fees. The part people leave out is that a fee is charged twice — once when you open and once when you close — so a 0.1% taker fee costs 0.2% of the round trip, not 0.1%. This calculator charges both sides, which is what your exchange statement will show.
ROI is that profit as a percentage of what you put in, so a $500 gain on $5,000 is 10% whether the asset was Bitcoin or anything else. The break-even price is the exit that leaves you exactly level after fees — always slightly above your entry, and further above it the higher the fee.
Worked example
Buy 0.5 BTC at $60,000 and sell at $77,000 with a 0.1% fee per side. The position costs $30,000 and returns $38,500, so the gross gain is $8,500. Fees are 0.1% of $30,000 plus 0.1% of $38,500 — $68.50 — leaving $8,431.50, an ROI of 28.1%. Break-even was $60,120, not $60,000.
Questions people ask
Does it handle short positions?
Enter the price you shorted at as the entry and the price you covered at as the exit. A profitable short shows a negative result here, because the calculator treats entry-to-exit as a long. Read the sign as the direction of the price move, not the direction of your trade.
What fee should I put in?
Use your exchange's taker fee unless you know your order rested on the book. Taker fees are typically 0.04% to 0.1% on the major venues; maker fees are lower and sometimes zero. If you are unsure, 0.1% is a safe upper bound for a spot trade.
Is anything sent to a server?
No. The calculation is JavaScript in your browser — no form is submitted, nothing is stored, and closing the tab loses it. Same principle as the app: your data stays on your machine.