How Markets Actually Work
What Happens Between Clicking "Buy" and Owning a Stock
It's Not as Simple as You Think
When you tap "Buy" on a trading app, it feels instant. But behind the scenes, a chain of events happens in milliseconds involving your broker, a stock exchange, market makers, and a clearinghouse. Understanding this process makes you a smarter trader.
Step by Step: What Happens When You Click "Buy"
- You place an order through your broker (Robinhood, Fidelity, Schwab, etc.)
- Your broker routes the order to an exchange or market maker
- A match is found — someone willing to sell at a price you'll accept
- The trade executes — you get the shares, they get the cash
- Settlement happens — the official transfer completes (usually 1 business day later, called T+1)
The whole execution part takes fractions of a second. But the details of how that match is found matter a lot.
The Order Book: Where Buyers Meet Sellers
Every stock has an order book — a live list of everyone trying to buy and sell that stock, organized by price.
| Buyers (Bids) | Price | Sellers (Asks) |
|---|---|---|
| $50.10 | 200 shares | |
| $50.05 | 500 shares | |
| 300 shares | $50.00 | |
| 800 shares | $49.95 | |
| 1,000 shares | $49.90 |
Buyers are stacked from highest price down. Sellers are stacked from lowest price up. When a buyer's price meets a seller's price, a trade happens.
The Bid-Ask Spread
The bid is the highest price someone is willing to pay right now. The ask is the lowest price someone is willing to sell for. The gap between them is the spread.
Example: Bid = $50.00, Ask = $50.05, Spread = $0.05
Why does the spread matter? - If you buy at the ask ($50.05) and immediately sell at the bid ($50.00), you lose $0.05 per share. The spread is a hidden cost of trading. - Popular stocks like Apple have tiny spreads (a penny or less). Tiny stocks nobody trades can have spreads of $0.10, $0.50, or more.
Market Makers: The Middle Men
Market makers are firms that keep the market running smoothly. They constantly post both buy and sell orders, providing liquidity — making sure there's always someone to trade with.
How they make money: they buy at the bid and sell at the ask, pocketing the spread thousands of times a day. It's like a currency exchange booth at the airport — they buy euros from you at one rate and sell them at a slightly higher rate.
Without market makers, you might place an order and wait hours for someone to show up on the other side.
Order Types: How You Tell the Market What You Want
| Order Type | What It Does | When to Use It |
|---|---|---|
| Market Order | Buy/sell immediately at the best available price | When you need the trade done NOW |
| Limit Order | Buy/sell only at your price or better | When you want to control the price |
| Stop Order | Triggers a market order when a price is hit | To limit losses or lock in gains |
| Stop-Limit | Triggers a limit order when a price is hit | When you want price control on your stop |
Pro tip: Use limit orders. Market orders during volatile moments can fill at prices you didn't expect.
Slippage: Why You Got a Different Price
Slippage is the difference between the price you expected and the price you actually got. It happens because:
- The market moved between when you saw the price and when your order arrived (even milliseconds matter)
- Not enough shares at that price — if you buy 1,000 shares but only 200 are offered at $50.05, the rest fill at higher prices
- High volatility — during big news events, prices jump around so fast that any market order is a gamble
Real example: During a big earnings surprise, you see a stock at $30 and hit buy. By the time your market order arrives, it's $31.50. That $1.50 difference is slippage.
Pre-Market and After-Hours Trading
Regular market hours are 9:30 AM - 4:00 PM Eastern, but trading doesn't stop there:
| Session | Hours (Eastern) | What to Know |
|---|---|---|
| Pre-Market | 4:00 AM - 9:30 AM | Lower volume, wider spreads |
| Regular Hours | 9:30 AM - 4:00 PM | Full liquidity, tightest spreads |
| After-Hours | 4:00 PM - 8:00 PM | Lower volume, wider spreads |
Why trade outside regular hours? - Earnings reports often come out at 4:00 PM or before the market opens - Big news breaks overnight - You want to react before everyone else can
The catch: Fewer traders means wider spreads, more slippage, and prices that can swing wildly on small trades. A stock might spike $5 after-hours on low volume, then settle back down by morning.
Key Takeaways
- Your buy order goes through a chain — broker, exchange, market maker, settlement
- The order book shows all pending buy and sell orders at every price
- The bid-ask spread is a hidden cost — tighter is better
- Limit orders protect you from slippage; market orders prioritize speed
- Pre-market and after-hours exist but come with thinner liquidity and higher risk
Practice: Test Your Knowledge
Question 1: A stock has a bid of $25.00 and an ask of $25.20. You buy 100 shares with a market order and immediately sell them. How much did the spread cost you?
Question 2: You place a market order to buy a stock you see priced at $40.00, but your order fills at $40.35. What happened, and what order type could have prevented this?
Question 3: Why might a stock's after-hours price not reflect what it opens at the next morning?
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