Saturday morning, 9:20, June 6. I sat on the kitchen stool with a spiral notebook I snagged for a dollar, a ruler, and printouts of fourteen trade confirmations fanned out like receipts from a bad month. The experiment was finished. The tally, in blue ink down the left margin, read $2.28. That is what my free trading week actually cost me.
Zero commissions are the entire sales pitch of my brokerage app, and I have repeated the pitch myself at dinner tables for three years without thinking twice. Fourteen orders. Ten shares here, five there. Never a fee. A broker is still a business, and businesses eat, so I wanted to trace where the money came from, which is how I ended up hand-copying every fill for seven trading days in late May and comparing each one to the national best bid and offer at the second I pressed buy.
One line in the notebook refused to behave. Order number seven, a limit order on a mid-cap tech name, filled at my exact price while every marketable order around it slipped a cent or two, and that difference in behavior turned out to be the entire story of the week. It took six days of staring at one page to see it.
where the free lunch eats
My broker, the one with the mascot and the zero banner, does not charge me cuz I'm not the customer. I am the inventory. Market makers pay brokerages for the right to see retail orders before the wider market does, an arrangement called payment for order flow, and they earn their keep on the spread, the gap between what you pay and what the next seller would have gotten. On paper it is a fraction of a penny per share. Fractions, multiplied across nine billion shares a day of market volume, stop being fractions.
nine minutes on an SEC page
The regulator keeps a plain-English page about this arrangement, and it took me nine minutes to read the whole thing, which is nine minutes more than I spent in 2021 when I opened the account. Marketable retail orders mostly route to wholesale firms, five sizable names handle the majority of them, and the wholesalers are required to fill at or better than the national best bid and offer. Price improvement is the promise. Improvement over what, exactly, never makes it onto the banner.
the notebook test
The rules I set were dull on purpose. Every order for one week would be ten shares or fewer, marketable at the moment I clicked, no exceptions, and nothing during the first or last fifteen minutes of a session when spreads get odd. I jotted down the quoted mid price, the actual fill, and the difference in cents per share, four times a day from my phone. Fourteen orders across eleven tickers, including an S&P 500 ETF three separate times because that is the thing I actually trade most. The notebook cost a dollar. The data felt worth ten.
order number seven, the odd one
Twelve of the fourteen orders filled exactly one cent worse than mid, which added up to $1.90 of invisible cost for the week, and two filled right at the mid. Order seven was one of those two, the only limit order I placed all week, priced a penny inside the spread and left to sit. It filled forty seconds later. A marketable order must be handled now, so it gets auctioned to whoever has paid the broker for the flow. A patient order sits on a public exchange, where nobody has paid for the privilege of seeing it first. That asymmetry is the whole game, printed in my own handwriting for a dollar.
1.9 cents, times everybody
Is $1.90 a week theft? No. My fills were legal, priced inside the rules, and honestly better than I anticipated before I began, and I chewed on that uncomfortable fact for two days before admitting the numbers were the numbers. But the same routing that cost me 1.9 cents a share also pays my broker somewhere between a tenth of a cent and half a cent per share to deliver the order, according to the disclosures I dug into afterward. Scale is the multiplier. A million-share pension block does not travel through this pipe, but the retail flood does, and 1.9 cents against hundreds of millions of retail shares a day buys alot of mascots and stadium signs.
the two accounts that never route
My 401(k) buys an index fund once a day at net asset value, and not one share of it crosses a wholesaler's desk, because mutual funds price once and settle once. Friction lives in frequency. Same with the Roth, where I hold a broad ETF but trade it twice a year, in slices, with limit orders, on quiet Tuesdays. The routing cost applies to the friction, and I had been generating friction weekly without noticing. The accounts I touch weekly cost pennies I never saw. The accounts I touch twice a year cost nothing at all.
Saturday, 9:20, same stool
This morning I closed the notebook, ruled a line under the $2.28, and wrote three words under it: limit, patient, done. The app stays. Zero is still approximately zero at my size, and $1.90 a week is a cheap education in how the plumbing works. What changed is the tempo. Orders that can wait go in as limits now, and the marketable clicks are reserved for the rare moments I truly need out the same hour. The notebook goes back in the drawer, sitting there until the next time a free thing makes me curious about the invoice.
