How a Trade Actually Happens

You tap "buy" on your phone. Seconds later, you own 100 shares of Apple. It seems instantaneous. But between your tap and your ownership, a remarkable journey takes place — one that reveals whose interests are aligned with yours, and whose aren't.

Step 1: You Place the Order

You open your brokerage app and decide to buy 100 shares of Apple. You see a quote: $185.50 bid, $185.52 ask. The spread — that two-cent gap — represents the market's transaction cost.

Before you click, you face a choice: what type of order?

Market Orders

A market order says: "I want to buy right now, at whatever price is available."

• Pro: Execution is virtually guaranteed (for liquid stocks)
• Con: You accept whatever price the market gives you

Limit Orders

A limit order says: "I'll buy, but only at this price or better."

• Pro: Price protection — you won't pay more than you specify
• Con: Your order might not execute if the price moves away

Step 2: Your Broker Receives the Order

When you tap "buy," you're not connecting directly to any exchange. You're sending your order to your broker, who then decides where to route it.

Your broker has a legal obligation called best execution — the duty to seek the best terms reasonably available. But "best execution" doesn't mean "best price." It's a multi-factor test leaving brokers considerable discretion.

And here's the conflict: your broker gets paid for sending your order to certain places.

Step 3: Payment for Order Flow

Your broker can send your order to several destinations: a public exchange, an ECN, a market maker, their own inventory, or a dark pool.

Most retail orders don't go to exchanges. They go to market makers through a practice called payment for order flow (PFOF).

Market makers pay your broker for the privilege of executing your order. Why would anyone pay for this? Because retail orders are profitable. Unlike institutional traders who may know something the market doesn't, retail traders are considered "uninformed" — their orders don't predict future price movements.

"The brokers had interests that were not necessarily aligned with the interests of their customers."

— Michael Lewis, Flash Boys

PFOF creates an obvious conflict: your broker is paid to send orders somewhere, regardless of whether that somewhere is best for you. The practice is banned in the UK, Canada, and Australia. As of 2026, it remains legal in the United States.

Step 4: The Order Book and Execution

Whether your order goes to an exchange or a market maker, it interacts with an order book — the queue of buy and sell orders at various prices.

Most investors see Level I data: the best bid and best ask. This is the National Best Bid and Offer (NBBO).

The spread is your first transaction cost. If Apple is $185.50 bid / $185.52 ask:

• You buy at $185.52 (the ask)
• You sell at $185.50 (the bid)
• Round-trip cost: $0.02 per share, or about 0.01%

For liquid stocks like Apple, spreads are tiny. For small-caps, spreads can be 1% or more — a meaningful drag on returns.

Step 5: Dark Pools

Not all trading happens on public exchanges. A significant portion occurs in dark pools — private trading venues where orders aren't visible until after execution.

Public exchanges broadcast order books: everyone can see the bids and asks. This transparency aids price discovery but creates a problem for large orders — displaying them publicly would be like announcing: "I'm a motivated seller!"

Dark pools hide order information until trades execute. As FINRA explains:

"The pools are called 'dark' because they don't broadcast pre-trade data — the presence, price and size of buy and sell orders — the way that traditional exchanges do."

Dark pools now account for roughly 15-18% of U.S. equity volume — significant enough to matter.

Step 6: Settlement — When You Actually Own It

Here's a surprise: when your trade executes, you don't immediately own the shares. Settlement — the actual exchange of cash for securities — happens later.

As of May 28, 2024, U.S. equities settle on T+1: one business day after the trade date. If you buy on Monday, settlement occurs Tuesday.

Settlement involves several entities:

1. Your broker confirms the trade
2. The NSCC acts as central counterparty, guaranteeing both sides
3. The DTC holds securities in electronic form and transfers ownership

When you "own" shares, what you actually have is an entry in your broker's books, which reflects an entry in DTC's books. Very few investors hold paper certificates anymore.

The gap between trade and settlement creates risks — the GME saga in January 2021 highlighted this when Robinhood had to halt buying because the settlement cycle created massive collateral requirements they couldn't meet.

The Complete Journey

Let's trace a typical retail order:

1. You click "buy 100 shares" on your phone
2. Your broker receives the order and decides where to route it
3. A market maker (probably Citadel or Virtu) receives the order via PFOF
4. The market maker executes your order against their inventory or hedges on an exchange
5. Confirmation comes back to you in seconds
6. Settlement occurs T+1 — cash leaves your account, shares appear
7. The DTC records that your broker holds those shares on your behalf

What feels like a single action involves multiple intermediaries, each taking a small piece.

What This Means for You

1. Understand what you're paying.
Commission-free trading isn't free. You pay through the spread and through PFOF-driven routing decisions.

2. Use limit orders when it matters.
For large orders, less liquid stocks, or volatile markets, limit orders protect you from unfavorable execution.

3. Check your broker's 606 report.
See where your orders go. High PFOF payments aren't necessarily bad, but they reveal the business model.

4. Know what you actually own.
Your shares exist as electronic book entries, held in your broker's name at the DTC. This is safe and standard, but understand that you're trusting several intermediaries.

5. Be skeptical of "price improvement" claims.
A penny of improvement means nothing if the quoted spread was artificially wide.

Looking Ahead

We've traced how a trade happens. But we skipped over a key player: the market maker.

In Part 5, we'll dive deep into what market makers actually do — how they profit, how they manage risk, and why their interests sometimes align with yours and sometimes don't.