What trading really costs

🎯 In 30 seconds: "Commission-free" does not mean free. Every round trip costs you the spread, some slippage, tiny regulatory fees on sales, and for many traders margin interest and options fees. Then taxes take a share of any short-term profit. Each item looks small. Added up over a year of active trading, they can easily come to several percent of a small account, which is a hurdle you have to beat before you make a single dollar. Count them before you trade, not after.

Why small costs matter so much

An investor who buys an index fund and holds it for ten years pays trading costs once or twice. A trader who makes 150 round trips a year pays them 150 times.

Costs are certain. Profits are not. If your trading idea earns a small edge per trade on average, costs can turn it into a loss. Research on individual investors makes the point: in a study of 66,465 US households at a discount broker from 1991 to 1996, Barber and Odean found the households that traded most earned 11.4% a year, while the market returned 17.9%. Trading costs were a large part of the gap.

Commissions

A commission is a fee your broker charges for executing a trade. Most large US brokers now charge $0 for online trades of US-listed stocks and ETFs. Many still charge commissions for broker-assisted trades by phone, some foreign stocks, mutual funds, bonds, and options. Check the fee schedule for every product you plan to trade.

The spread: the cost you pay every round trip

You buy at the ask and sell at the bid. If the price does not move, you lose the difference. For a stock quoted $39.99 bid and $40.01 ask, the round trip costs $0.02 a share.

The spread is paid half on the way in and half on the way out, measured from the midpoint. You never see it on a statement.

For large, busy stocks the spread is often a cent or two. For small, thin stocks it can be several percent. Bid, ask and liquidity shows how to measure it.

Payment for order flow and execution quality

Many $0-commission brokers are paid by wholesalers to send them customer orders. This is payment for order flow (PFOF). The wholesaler earns money from the spread and usually gives some price improvement: a fill slightly better than the quoted bid or ask.

The cost to you is not a line item. It is the difference between the price you got and the best price you could have got. SEC staff have flagged the conflict of interest: a broker could favor the venue that pays it most over the one that gives you the best fill. Brokers publish quarterly Rule 606 reports showing where they route orders and what they receive. See Choosing a broker.

Regulatory fees on sales: Section 31 and FINRA TAF

Two small fees are charged only when you sell. Brokers usually pass them through to you on the trade confirmation.

SEC Section 31 fee. Exchanges and FINRA pay this fee to the SEC to fund it, based on the dollar value of sales. The rate changes during the year as the SEC adjusts it to hit a funding target set by Congress. As of October 2026, it is $20.60 per million dollars of sale proceeds, in effect since April 4, 2026. Before that date in fiscal 2026 it was $0.00. The rate stays until 60 days after Congress sets the SEC's fiscal 2027 budget, so check the SEC's fee rate advisories for the current figure.

Section 31 fee = sale proceeds x 20.60 / 1,000,000

Selling $4,000 of stock: $4,000 x 0.0000206 = about $0.08.

FINRA Trading Activity Fee (TAF). FINRA charges this on sales to fund its oversight. The 2026 rates are $0.000195 per share for stocks, with a maximum of $9.79 per trade, and $0.00329 per contract for options sales. In September 2026, FINRA filed to pause the TAF at $0.00 for trades from October 1 through December 31, 2026, because collections were running above budget. It is set to resume at the same rates on January 1, 2027. Your broker may or may not have passed the pause through to you.

Selling 100 shares: 100 x $0.000195 = about $0.02 (outside the pause).

Options costs

Options add several fees per contract. A contract usually covers 100 shares, so fees are counted per contract, not per share.

Per-contract commission charged by the broker, even at many $0-commission brokers.
Exchange and clearing fees, including the options regulatory fee charged by exchanges and a clearing fee, often passed through.
FINRA TAF on options sales, as above.
Exercise and assignment fees at some brokers.
Wider spreads. Options spreads are often much wider than stock spreads in percentage terms, which usually costs more than all the fees combined.

See Reading an options chain for how to judge an option's spread.

Margin interest, ADR fees and other charges

Margin interest. If you borrow from your broker, you pay interest daily on the balance. Rates vary widely between brokers and usually fall as the amount borrowed rises. On a small account, margin interest is often the largest cost of all. See Margin explained.

ADR fees. Many foreign companies trade in the US as American Depositary Receipts. The depositary bank can charge a custody fee per share, usually taken out of dividends or, if there are no dividends, billed through your broker. Banks may also charge for dividend distribution and currency conversion.

Account fees. Transfer-out fees if you move to another broker, wire fees, paper statement fees, real-time data subscriptions, and foreign currency conversion spreads.

Cash drag. Uninvested cash that earns little interest costs you what it could have earned in a money market fund. Check what your broker pays on idle cash.

Taxes: the biggest cost for a profitable trader

In a taxable account, profits on positions held one year or less are short-term capital gains, taxed at your ordinary income tax rate. Positions held longer than a year get lower long-term rates. Active trading almost always produces short-term gains.

Hypothetical example: you net $1,500 of trading profit in a year. If your marginal federal rate is 22%, the tax is $330. If the same profit had been long-term at a 15% rate, it would be $225. State tax may add more. The wash sale rule can also delay losses you thought you could deduct. See Taxes for traders.

Worked example: one year of active trading

All numbers are hypothetical, except the regulatory fee rates. A trader has a $10,000 margin account. Over a year they make 150 round trips in stocks, each 100 shares of a stock around $40 (a $4,000 position). They pay $0 commission. They also make 20 options round trips of 2 contracts each.

Spread: 150 x 100 shares x $0.02	$300.00
Extra slippage on 40 stop-outs: 40 x 100 x $0.03	$120.00
Section 31 fee: 150 sales x $4,000 x 20.60 / 1,000,000	$12.36
FINRA TAF: 150 sales x 100 x $0.000195 (if charged all year)	$2.93
Options commission: 20 x 2 contracts x 2 sides x $0.65 (assumed rate)	$52.00
Margin interest: $3,000 average borrowed x 11% (assumed rate)	$330.00
Stock commissions	$0.00
Total before taxes	$817.29
As a share of the $10,000 account	8.2%

This trader must make about 8% on the account just to break even, before any tax on profits. For the stock trades, spread, slippage and fees come to about $2.90 per round trip on a $4,000 position, so each trade has to gain about 0.07% just to cover them. Add the margin interest and it is about $5.10 per round trip, or 0.13%.

For this trader, borrowing costs and the spread dwarf the regulatory fees. Cutting margin use and trading less often would remove most of the bill.

The mistake: counting only commissions

A $0 commission does not make a trade free, and a high trade count multiplies every hidden cost. Before you judge whether a strategy works, subtract realistic spread, slippage, fees, interest and tax from its results. A strategy that looks good before costs and loses money after them does not work.

Four ways to cut costs

Trade liquid stocks with tight spreads. Use limit orders. Trade less often, so each trade has a real reason. Avoid margin until you have a proven, profitable record, and if you use it, compare rates across brokers.

Try it

Copy the worked example table and fill it in with your own plan: trades per year, typical position size, typical spread of the stocks you watch, whether you will use margin and options. Then add a column to your trading journal for costs on every trade. When you test an idea in the backtester or the paper portfolio, subtract your yearly cost estimate from the result before you decide it works.

Check yourself

Which two small regulatory fees are charged only when you sell? Answer: The SEC Section 31 fee and the FINRA Trading Activity Fee (TAF).
At $20.60 per million dollars of sales, what is the Section 31 fee on a $4,000 sale? Answer: About $0.08 ($4,000 x 20.60 / 1,000,000).
You net $1,500 of short-term trading profit and your marginal federal rate is 22%. What is the federal tax, and what would it be as a long-term gain at 15%? Answer: $330 at 22%, or $225 at 15%.
In the chapter’s one-year example, what were the two biggest costs, and what share of the $10,000 account did all costs take before taxes? Answer: Margin interest ($330) and the spread ($300). All costs came to $817.29, about 8.2% of the account.

🧾 What trading really costs