Here’s a small, mildly annoying truth about stock trading that beginners underestimate and experienced traders occasionally forget when they’re being lazy: the price on your screen minus the price you paid is not your profit. It’s your gross gain per share. Commissions eat into it, and if you’re trading a meaningful position size across multiple lots, that bite is bigger than most people assume until they actually sit down and add it up.
This calculator does that addition for you — entry price, exit price, share count, and commissions on both the buy and the sell, netted out to what you actually walk away with. I built the default commission structure around Interactive Brokers‘ Tiered pricing, which charges $0.0035 per share with a $0.35 minimum per order, because it’s one of the more transparent per-share models in the industry and a lot of active traders are on it or something functionally similar. But the fee field is fully editable — if you’re on a flat-fee broker, IBKR Lite’s zero-commission structure, or something with a different tier schedule entirely, just type in what your broker actually charges.
How to Use It
Entry price and exit price — what you paid per share and what you sold it for. Straightforward.
Number of shares — your position size.
Commission per share ($) — defaults to $0.0035, matching IBKR Tiered pricing. This is a per-share rate, not a flat fee, which is the detail that catches people off guard the first time they look closely at a fill confirmation from a per-share broker.
Minimum commission per trade ($) — defaults to $0.35, also matching IBKR’s minimum. On a small trade, the per-share rate alone would round to pennies, so brokers set a floor. This field exists because that floor matters disproportionately on small positions and gets forgotten entirely on large ones.
Apply commission to both entry and exit — toggle this on (it’s on by default) if your broker charges you on both the buy and the sell, which is standard for basically every broker that charges commission at all. Turn it off only if you’re specifically modeling a scenario with a one-sided fee, which is rare.
Run it and you’ll get your gross profit (before fees), total commissions paid, net profit (after fees), and your net return percentage — plus a breakeven price showing exactly what the stock needs to close at for the trade to wash out to zero after costs.
Where People Actually Screw This Up
Forgetting commissions scale with share count in ways percentage-based thinking doesn’t capture. A $0.35 minimum commission on a 50-share trade is basically a rounding error. That same rate structure on a 10,000-share trade adds up to real money fast, and if you’re trading in and out frequently, those per-share fees compound across dozens of round trips in a way that a single “seems cheap” transaction never reveals on its own.
Treating the entry price as the true cost basis. If commission applied on the buy side, your actual cost basis is entry price plus that commission, not just the sticker price you saw on the order ticket. This matters more for tax reporting than people expect — brokers generally adjust your reported cost basis to include commissions, so the number on your 1099 won’t always match the raw entry price you remember typing in.
Ignoring the difference between gross return and net return on percentage-based thinking. A stock that moved from $50 to $52 “gained 4%,” and that’s true at the share-price level. Once commissions come out of a modest position, the net percentage return you actually captured is measurably lower than the headline number, especially on lower-priced, smaller-position trades where fixed minimums eat a bigger relative chunk.
Assuming zero-commission means zero cost. Commission-free brokers still make money somewhere, commonly through payment for order flow, which can show up as a marginally worse fill price than what a directed-routing broker gets you. It’s not the same line item as an explicit commission, and this calculator doesn’t attempt to model it, but it’s worth knowing it’s not strictly a free lunch just because the commission field reads zero.
Not accounting for wash sales when reviewing losing trades. If you sell at a loss and buy back a substantially identical position within 30 days, the loss may be disallowed for tax purposes under wash sale rules. This calculator computes trade-level profit and loss, not tax treatment — a realized loss here isn’t automatically a deductible loss on your return.
Quick Reference
Gross profit — (exit price − entry price) × shares, before any costs are subtracted. The number most people mean when they casually say “I made $X on that trade.”
Net profit — gross profit minus total commissions. The number that actually lands in your account.
Breakeven price — the exit price at which net profit equals exactly zero, accounting for commissions on both sides of the trade. Useful for setting realistic profit targets that account for the fee drag baked into every round trip.
Round trip — trader shorthand for a complete buy-then-sell cycle on a position. Commissions on a round trip are the sum of both legs, which is why the “apply to both entry and exit” toggle exists.
Frequently Asked Questions
Does this calculator account for capital gains tax?
No, and intentionally so — tax treatment depends on your holding period (short-term vs. long-term), your tax bracket, your account type (taxable vs. IRA), and jurisdiction, none of which a generic calculator can responsibly assume on your behalf. This tool shows trade-level profit and loss only. For actual tax planning, run the net profit number through your specific tax situation or talk to someone who does that for a living.
Why is my broker’s confirmation showing a slightly different commission than what this tool calculated?
A few possibilities: your broker may pass through additional exchange, regulatory, or clearing fees on top of the base commission rate (common on tiered pricing plans), you may have hit a different volume tier than the default rate assumes, or there’s a small SEC transaction fee applied to sell orders that most calculators, including this one, don’t model since it’s a fraction of a cent per hundred dollars of proceeds. Close-but-not-identical numbers are almost always one of these, not a bug.
Should I use this for day trading or is it better suited to swing/position trades?
It works fine for either — the math doesn’t care about your holding period. Where it becomes especially useful for day traders specifically is running several quick what-if scenarios before pulling the trigger on high-frequency, small-margin trades, where commission drag as a percentage of profit is disproportionately larger than it is on longer-held swing positions.
How does this differ from the position size calculator on this site?
The position size calculator answers “how many shares should I buy given my risk tolerance and stop-loss.” This tool answers “given a trade I already made or I’m considering, what’s my actual profit after fees.” They’re complementary — size the trade with one, evaluate the outcome with the other.
Can I model a short sale with this calculator?
Not directly — this tool assumes a standard long buy-then-sell sequence. Short selling involves borrowing costs and margin considerations this calculator doesn’t account for, and modeling it accurately would need a separate tool built around that mechanic specifically rather than bolted awkwardly onto this one.
