Market, limit and stop orders, and when each one hurts you

An order type is an instruction about what you will accept. Every one of them guarantees something and refuses to guarantee something else, and the whole skill is knowing which trade you are making.

The previous piece followed an order from the app to a fill and introduced the bid, the ask and the spread. This one is about the instruction you attach to it.

The market order: certainty of execution

A market order says fill me now at whatever the book offers. It almost always executes, and it makes no promise at all about price.

In a heavily traded company during regular hours, the difference between the price you saw and the price you got is usually trivial, because the spread is a cent and there is size at every level. That is the case a market order is built for.

Where it hurts. Three situations, and they compound.

• Thin names. Few shares at each level means your order walks up the book and your average fill drifts well past the ask you saw.
• Outside regular hours. Spreads widen and depth thins, so the same order costs more.
• Around news. The book empties as market makers pull quotes. A market order into that can fill far from where you expected.

The failure mode is always the same shape: you got filled, and the price is worse than you assumed. Nothing malfunctioned. You asked for speed and the market charged you for it.

The limit order: certainty of price

A limit order sets the worst price you will accept. A buy limit at 48.50 means fill me at 48.50 or better, never worse. A sell limit at 52 means 52 or better.

If the market is already at or through your limit, it behaves much like a market order with a ceiling. If it is not, the order sits in the book and waits.

Where it hurts. It does not fill. The price came within a cent, turned, and went where you thought it would go without you. That is the trade you accepted: you protected the price and gave up the certainty of getting in.

The second, subtler failure is a partial fill. You wanted five hundred shares at 48.50, two hundred traded there, the price left, and you are holding a smaller position than the plan assumed. If your sizing was built around five hundred, the position is now wrong in a way that is easy to ignore.

A limit order is the right default for most retail trading. Thin names, volatile sessions and anything outside regular hours, it is close to mandatory.

The stop order: a trigger, not a price

This is the one that is most often misunderstood, and the misunderstanding is expensive.

A stop order is dormant. It has a trigger price, and nothing exists in the book until the market trades there. When it triggers, the stop becomes an order, and which kind it becomes is the whole question.

Stop market

Triggers, then becomes a market order. It will get you out. It makes no promise about where.

If a company opens sharply lower than it closed, a stop sitting above the open does not fill at the stop price, because the market never traded there. It triggers and fills at whatever the book offers on the open, which can be a long way down. This is the single most common unpleasant surprise in retail trading, and it is behaving exactly as designed.

Stop limit

Triggers, then becomes a limit order at a price you set. It protects the price and gives up the certainty of exit.

That protection has a sharp edge. If the price gaps straight through your limit, you do not get out at all, and you are still holding as it keeps going. A stop limit can leave you in the exact position the stop existed to end.

Neither is safer in general. A stop market accepts a bad price to guarantee the exit. A stop limit accepts no exit to protect the price. Choose deliberately and know which one you chose.

A worked example, because the difference is easier to see in numbers

A company is quoted 47.98 bid, 48.02 ask. There are 300 shares at the ask, then 900 at 48.06, then 2,000 at 48.11. You want 1,000 shares.

• Market order. You take 300 at 48.02 and 700 at 48.06. Average fill 48.05. You own 1,000 shares and paid about three cents a share more than the quote suggested.
• Limit at 48.02. You get 300 shares. The other 700 rest in the book. If the price runs, you are holding 300 shares against a plan written for 1,000.
• Limit at 48.10. You get 1,000 shares at an average close to 48.05, the same as the market order, with a hard ceiling if something ugly happens in the half second your order is travelling.

That third one is the useful pattern. A limit set slightly beyond the current ask behaves like a market order in normal conditions and refuses to fill at a catastrophic price in abnormal ones. It is sometimes called a marketable limit, and it removes the worst outcome of a market order while keeping almost all of the certainty.

The trailing stop

A trailing stop sets its trigger at a distance from the best price reached, rather than at a fixed level. Set a dollar below on a position that rises from 50 to 56, and the trigger follows to 55.

It never moves against you. If price falls, the trigger stays where it was. The appeal is that it locks in progress without requiring you to watch, and the cost is that the distance is chosen by you rather than by the chart, so it can sit somewhere structurally meaningless.

A trailing stop too tight for the instrument gets hit by ordinary noise. Too wide and it gives back most of the move. The distance should come from how much this particular thing moves in a normal day, which is a measurement rather than a preference.

Instructions about how much, and when

Beyond price, most brokers offer conditions on quantity and timing. Two are worth knowing.

• All or none. Fill the whole quantity or nothing. Useful when a partial position is genuinely worse than none, and a good way to never get filled in a thin name.
• Fill or kill. Fill the whole quantity immediately or cancel. Rarely what a retail trader wants.

There are also orders aimed at the opening and closing auctions, which are single moments when a large volume trades at one price. Those matter more to institutions than to most retail traders, though the closing auction is why the last minute of the session often carries unusual volume.

Day, good til cancelled, and the clock

Every resting order carries a duration. A day order expires at the close of the session. A good til cancelled order stays alive across sessions, usually for a broker defined maximum.

Resting orders left alive across days are worth reviewing. A limit set for one week's reasoning can trigger a fortnight later into a situation nothing like the one you planned for, and it will do so without asking.

Where a stop should sit, and where it should not

An order type decides how you exit. Where you put the trigger decides how often you exit for no good reason, and that is a separate skill.

Two bad habits are almost universal among new traders. The first is a stop at a fixed percentage below entry, chosen because it sounds disciplined. A fixed percentage takes no account of how much this particular instrument moves in an ordinary day, so on a volatile name it is inside the daily noise and on a quiet name it is far too loose.

The second is a stop just below a round number. Round numbers attract resting orders from everybody, which makes the area just below them thick with stops, which makes it a place price frequently reaches and then leaves. Putting your stop where the crowd put theirs means being taken out with the crowd.

A better question is structural. What price would mean the reason you entered is no longer true? If you bought because a level held, the stop belongs below that level, far enough that ordinary movement does not reach it. If you cannot name the level, you do not have a stop, you have a number.

Position size follows the stop, not the other way round

Once the stop is placed by structure, the distance from entry to stop is fixed by the chart rather than by preference. The variable you still control is how many shares you buy.

That is the correct order of operations, and most people do it backwards. They decide the size first, then place a stop where the resulting loss feels tolerable, which puts the stop somewhere the chart does not care about. Deciding the stop first and sizing to it keeps the risk constant while letting the market define the level.

Risk per trade gets its own piece later in this series. The order matters now, because it determines whether your order types are protecting a plan or improvising one.

Slippage on the way out is worse than on the way in

Entries are voluntary. You choose the moment, and if conditions are ugly you can decline.

Exits are frequently not. A stop triggers when the market decides, which is disproportionately during fast, one sided moves, when the spread is wide and the book is thin. The order type that costs the least on a calm entry can cost the most on a violent exit.

Anyone planning an exit should assume conditions worse than the ones they can see, because the conditions that trigger the exit are the ones that made it necessary.

A practical default

Nothing here is advice about what to trade. It is a way of choosing an instruction once you have decided.

• Entering a liquid name in regular hours and the exact tick is not critical: a market order is fine.
• Entering anything thin, volatile, or outside regular hours: a limit order.
• Defining risk on a position you cannot watch: a stop, having decided consciously whether exiting or the price matters more.
• Any order left resting overnight: written down, with the reason, and reviewed before the next open.

How the Den uses this

Every alert in the rooms carries an entry range and a structural stop, and both exist because of this piece. A range is a limit instruction in words: here is the band where the idea is valid. A structural stop is a level chosen because the reasoning fails there, not because it is a round number or a fixed percentage below the entry.

That distinction decides how often you get stopped out of ideas that were right. A stop at a round number sits where everyone else put theirs, which is exactly where price goes looking. A stop under the level that made the trade make sense is somewhere the market has to genuinely break to reach.

The post mortem room is where the order type usually turns out to be the culprit. A trade that looks like a bad idea often turns out to be a reasonable idea with a market order into a thin open, or a stop limit that never filled. Those are fixable, and they are only fixable if the write up records which instruction was used.

Read a few of those before you place an order you cannot watch. It is a cheaper way to learn this than the direct one.