Market vs limit orders

THE TWO ORDER TYPES

A market order is an instruction to your broker: "buy/sell at the best available price right now." The order executes immediately, at whatever the current bid (if selling) or ask (if buying) happens to be. You get certainty of execution. You give up certainty of price.

A limit order is an instruction with a price condition: "buy/sell only at this price or better." The order goes onto the order book and waits. If the market reaches your price, you fill. If it doesn't, you don't fill. You get certainty of price (or better). You give up certainty of execution.

That's the entire mechanical distinction. Everything else is about which to use when.

THE PRACTICAL DIFFERENCE

In a liquid stock with a 1-cent spread, the choice barely matters. If Apple is trading bid $245.30 / ask $245.31, a market buy fills at $245.31 and a limit buy at $245.31 also fills at $245.31. The market order is faster (no waiting for a counterparty to come to you), but the price difference is pennies.

In a less liquid stock with a 5-cent spread, the choice matters more. If a small-cap is bid $18.40 / ask $18.45, a market buy fills at $18.45. A limit buy at $18.42 might fill if a seller drops their offer, or might never fill if the spread stays wide. You pay 3 cents extra for guaranteed execution, or you save 3 cents and accept the risk of not filling.

In an illiquid stock with a 30-cent spread, the choice matters a lot. A market order in a thinly-traded $25 stock with a 30-cent spread costs you 1.2% of the price just on the spread, plus potentially more if your order is large enough to "walk the book" (consume multiple levels of the order book before filling). A limit order at the bid prevents this entirely, if you fill, you fill at your price; if you don't, you don't.

THE DECISION RULE

For BiST readers, here's the rule that handles 95% of order-placement decisions:

Use limit orders by default. Use market orders only when the spread is essentially zero (under 0.05% of the price) AND you need immediate execution.

That's it. Not complicated.

In practice, this means:

• Trading Apple, Microsoft, Costco, Nvidia, or other megacap names with penny spreads: market order is fine. The spread is so tight that the price improvement from a limit order is negligible.
• Trading a small-cap or mid-cap name with a 0.10% or wider spread: use a limit order. Set the limit at the current bid (when buying) or ask (when selling), you'll often fill at a better price than the market order would have given you.
• Trading any stock during pre-market or after-hours: use a limit order regardless of normal spread, because liquidity drops sharply outside regular hours.
• Triggering a stop-loss: market orders are typical for stop-losses (the goal is execution, not price), but in less liquid names, a stop-limit order can prevent slippage at the cost of risking non-execution. We'll cover stop-loss mechanics in detail tomorrow.

THE MINERVINI RULE

Mark Minervini, the two-time U.S. Investing Champion (1997, 2021) we'll feature extensively in Month 8, has a stricter rule than the one above. From his book Trade Like a Stock Market Wizard:

"I never use market orders except in cases of dire emergency. The cost of bad executions, compounded over thousands of trades, is enormous."

Mark Minervini, Trade Like a Stock Market Wizard (2013)

Minervini's reasoning: even in liquid stocks, the discipline of placing limit orders forces you to be intentional about your entry price. A market order is a small abdication of judgment, "whatever the price is, that's the price." A limit order is a small assertion of judgment, "I'm willing to buy at this price, no worse." Done thousands of times across a career, the limit-order discipline produces measurably better entries on average.

For a beginner, this might be too strict, limit orders sometimes don't fill, and missing a fill on a stock that subsequently runs is its own form of cost. But the principle is sound: default to limit orders, and treat market orders as the exception that requires justification.

A NOTE ON ORDER MODIFIERS

Beyond market and limit, your broker offers a set of modifiers that change how an order behaves. The two worth knowing now:

Day order: the order is good only for today's trading session. If it doesn't fill by the close, it's automatically canceled. This is the default for most order types.

GTC (Good-til-Canceled): the order remains active for up to 60-180 days (depending on the broker), or until you cancel it. Useful when you want to set a buy-limit below the current price and let it sit, or to set a sell-limit above the current price as a take-profit target.

There are more (Fill-or-Kill, Immediate-or-Cancel, Iceberg orders, etc.), but they're meant for institutional and high-frequency traders. For the trading patterns this newsletter teaches, day orders and GTCs cover essentially everything.

EXAMPLE WALKTHROUGH

Let's say you've decided to buy 100 shares of Costco (COST), currently bid $958.40 / ask $958.42, a 2-cent spread.

Approach 1, Market order: click Buy 100 at Market. You fill at $958.42 (the ask). Total cost: $95,842.

Approach 2, Limit order at the bid: Place a Buy Limit 100 at $958.40, GTC. The order joins the bid level. If a seller drops to $958.40, you fill at that price. Total cost if filled: $95,840, saving $2 vs. the market order.

The savings are tiny in absolute terms ($2 on a $95,842 trade is 0.002%). For a megacap with a 2-cent spread, both approaches are essentially the same. But: if you do the same trade 50 times across a year, you save $100 in expected execution cost. Across thousands of trades over a career, that compounds to real money.

This is why disciplined traders use limit orders by default even when the spread looks negligible. The discipline is free, and the small savings compound.