Buy 100 shares at $50, sell them at $60, and the screen says you made $1,000. Run the same trade through a real fee schedule, a $0.0035-per-share commission with a $0.35 minimum on each side plus the SEC and FINRA fees that apply on the sell, and the number is $999.24. The gap is 76 cents. Nobody trading in round lots of 100 shares or more needs to lose sleep over that.
Drop the size to 10 shares of the same trade and the arithmetic changes in a way most calculators do not explain. Fees come to $0.71 against a gross gain of only $100, a drag of 0.71%, nearly 9.2 times heavier than the 100-share version. Nothing about the fee schedule changed. What changed is that ten shares was never enough to clear the $0.35 minimum on a per-share basis, so the minimum did the pricing instead of the rate.
A stock profit calculator exists to close the gap between the headline number and the one that actually lands in the account. The subtraction itself is simple. Knowing which fees belong in it, and which ones only matter once an order gets small or gets split into pieces, is the part worth understanding before you type numbers into any version of this tool, on this site or anywhere else.
Where the minimum takes over
The math behind a stock profit calculator is short: gross gain equals the exit price minus the entry price, times shares, and net profit subtracts commissions and regulatory fees from that. The commission side usually has two components, a per-share rate and a per-order minimum, and the calculator applies whichever is larger. At $0.0035 a share, the rate crosses the $0.35 minimum at exactly 100 shares. Below that line, the minimum sets the price and the fee is effectively fixed no matter how few shares you traded. Above it, the fee scales with size and the percentage drag barely moves.
Most people size a trade around a dollar amount they are comfortable risking, not a share count, which means the 100-share threshold sneaks up on them from the wrong direction. A $500 position in a $50 stock is exactly 10 shares, squarely inside the zone where the minimum dominates. The same $500 in a $5 stock is 100 shares, right at the crossover. Position size and share count are not the same variable, and this calculator only sees the second one.
| Shares | Gross gain | Commission (round trip) | SEC + FINRA fees | Total fees | Net profit | Fee drag |
|---|---|---|---|---|---|---|
| 10 | $100.00 | $0.70 | $0.006 | $0.71 | $99.29 | 0.7065% |
| 100 | $1,000.00 | $0.70 | $0.065 | $0.76 | $999.24 | 0.0765% |
| 1,000 | $10,000.00 | $7.00 | $0.646 | $7.65 | $9,992.35 | 0.0765% |
| 10,000 | $100,000.00 | $70.00 | $6.460 | $76.46 | $99,923.54 | 0.0765% |
Look at the drag column, not the fee column. It falls from 0.71% at ten shares to 0.0765% at one hundred, then holds almost exactly flat at 0.0765% for a thousand shares and 0.0765% for ten thousand. That flatness is the real finding here. Once an order clears the minimum, size stops being the variable that determines what fees cost you as a share of profit. Order count does.
Regulatory fees are the smaller, fixed part of the bill
Two fees ride along on every sale beyond the broker’s own commission: the SEC fee, assessed on total proceeds and running roughly $8 per $1,000,000 sold under the rate the SEC sets periodically, and the FINRA trading activity fee, a small fraction of a cent per share sold, capped at $8.30 per trade. On the 100-share example, that combination adds up to about 6 cents. On the 10,000-share example it is $6.46. Neither one is the line item that changes your answer. The commission structure is. If your calculator shows a big number for “regulatory fees,” check that it is not double-counting the per-share commission under a different label.
A position size calculator answers a different question, how many shares to buy given your risk tolerance, but the two tools are meant to be used together. Size the position first, then run the exit through this one before you decide the trade was worth the risk you took sizing it.
Commission scales the way you would expect, linearly with shares once the minimum stops binding, which is why the bar chart above looks like a straight staircase rather than a curve. The fee side does not scale the same way at every broker. Some charge a flat rate per trade regardless of size, which flips this entire analysis: a flat-fee broker makes a 10-share trade relatively cheap and a 10,000-share trade relatively expensive, the opposite of the per-share model shown here. Read your own broker’s schedule before assuming either shape applies to your account.
Multiple lots multiply the minimum, not just the math
Here is the part that actually costs active traders money: scaling into a position across several separate orders resets the minimum each time. Buy 25 shares four separate times instead of 100 shares once, and you pay four times the $0.35 minimum on the way in, $1.40 instead of $0.35, before you have sold a single share. Do the same thing scaling out on the sell side and the round-trip commission on what was originally a single 100-share idea can run three or four times higher than the $0.70 shown in the table above. The fee schedule never changed. The order count did, and the calculator can only tell you the cost of the orders you actually enter.
That is also where a stock average price calculator becomes useful alongside this one: if you are buying in tranches to build an average cost basis, tracking the blended entry price separately from the running commission total keeps the two kinds of math from blurring together in your head. A blended cost basis tells you what you paid on average. It says nothing about what you paid to get there in fees, and conflating the two is how traders convince themselves a strategy is working when the entry cost alone is quietly eating the edge.
Options traders run into a version of the same problem from a different angle. A ten-lot options order is ten contracts, not ten shares, and most brokers charge per contract rather than per share, so the crossover point where a minimum fee stops mattering sits at a completely different number than it does here. Treating an options fill like a stock fill, or vice versa, is one of the more common mistakes beginners make when they reach for whichever calculator is already open in another tab.
What this calculator will not do
It will not tell you what you owe in taxes, and that gap is larger than the commission gap in almost every case above. A position held one year or less is taxed as short-term capital gains, at your ordinary income rate. Hold it longer and it qualifies for the lower long-term capital gains rate instead. On a $1,000 gain the difference between those two treatments is usually the single largest number in the entire transaction, dwarfing the 76 cents of commissions and fees this calculator nets out. Nothing here substitutes for checking your own bracket before you file.
Wash sale rules are the other omission worth naming. Sell a losing position and buy back a substantially identical one within thirty days on either side of the sale, and the loss you were planning to use against other gains can be disallowed for the current tax year. A profit calculator has no way of knowing what else is in your account or what you plan to buy next week, so it will show you a clean loss figure that your tax return may not be able to use yet.
It also will not price options contracts, where per-contract fees and a $100 multiplier change the arithmetic entirely; the options profit calculator handles that math separately rather than folding it into the equity version. And it assumes your fills happen at the price you type in, which is rarely exact once slippage on a fast-moving stock is added to the picture. For a broader look at building a research process that catches those gaps before they cost real money, our guide to stock research tools is a reasonable next stop.
The line this calculator leaves for your tax software
Run your own numbers through it once at the size you actually trade, not the round 100-share example above. If the fee drag comes back close to 0.08%, the minimum is not costing you anything and the number on the screen is close enough to real. If it comes back several times higher, count your orders before you blame the broker. Either way, the figure this calculator hands you is pre-tax, and that is the number to carry into whatever you use to file, not the one to mistake for what lands in your account.
One more habit worth building: rerun the same trade through the calculator at your actual number of separate fills, not the tidy single-order version. If a position was built across six small buys and closed across three sells, plug in nine orders instead of one and watch how much of the round-number profit the minimum quietly claws back. That nine-order version is usually the honest one, and it is the one that should decide whether the strategy behind it is actually worth repeating.
Financial disclaimer: The content on StockVane is for educational and informational purposes only and should not be construed as professional financial advice. Stock market investing involves risk of loss.
Sources: Price-to-earnings ratio (SEC Investor.gov glossary) (https://www.investor.gov/introduction-investing/investing-basics/glossary/price-earnings-pe-ratio) · Stock options tax topic (IRS) (https://www.irs.gov/taxtopics/tc427)