Marketable limit orders: paying up with a ceiling

Start in plain English

A marketable limit order is a limit order priced so that it can trade immediately: a buy limit at or above the current ask, or a sell limit at or below the current bid. SEC rules define it the same way, measured against the best quote when the order arrives. Scalpers use it to "pay up" for a fast fill without handing the market an unlimited price.

The core idea: the limit price is a ceiling, not a target. A buy limit at ask + $0.05 takes every offer up to that ceiling, like a market order, and stops there. Anything the ceiling cannot reach stays unfilled. So the ceiling trades fill certainty for price control: higher ceilings fill more often and cost more per share when they do.

The difference between "market vs. limit" in general belongs to the Market vs. limit orders lesson in US Day Trading Fundamentals. This lesson covers how a scalper chooses the ceiling, sizes from it, and handles the partial fills it produces.

Two paths from the same start

All prices, books, sizes and costs in this example are Illustrative. Teasel Robotics is fictional.

The setup at 10:02:15 ET. Teasel Robotics is quoted $3.11 × $3.12. The trader wants 800 shares.

The plan, written before 10:02. Buy 800 shares with a limit at $3.17 (ask + $0.05), time in force IOC (immediate or cancel: whatever cannot fill at once is cancelled). Stop $3.05. Target $3.31. Planned risk is measured from the ceiling: $3.17 − $3.05 = $0.12 per share, $96 at 800 shares (1R). Commissions and fees $0.005 per share round trip.

The review note for all three: "Plan followed; ceiling ask + 5 cents; IOC; did not chase." Same decision, three order outcomes. Notice the pattern in this example: the fill was smallest exactly when demand was strongest. Each of these order outcomes can also meet a move that fails; the "Cost of being wrong" table below shows both sides. The rest of the lesson covers how to choose the ceiling, why size comes from the ceiling, what to do with partial fills, which time in force to use, and how halts and LULD bands change the picture.

Choosing the ceiling

The ceiling is the most you accept per share above the arrival ask. It sets your maximum entry slippage, so it works together with Slippage:

• Too tight (ask + $0.01 on a fast stock): frequent partial fills and misses, mostly on the moves that ran.
• Too loose (ask + $0.20 on a $3 stock): fills most of the time, and in a thin book it can fill far up the ladder, eating much of a 15–20 cent target.

Common ways to set it, each a choice to test rather than a rule:

Below $1, use four decimals: ask $0.4125 with a $0.0050 offset gives a $0.4175 ceiling.

Size from the ceiling, not from the ask

If you size from the ask, a fill at the ceiling breaks your risk plan. With $100 of planned risk, an ask of $3.12 and a stop at $3.05:

• Sized from the ask: $100 ÷ $0.07 = 1,428 shares. If the order fills near the $3.17 ceiling, the real risk is $0.12 × 1,428 ≈ $171, about 1.7 times the plan.
• Sized from the ceiling: $100 ÷ $0.12 = 833 shares, rounded down to 800 in this plan. A worst-case fill at the ceiling still respects the $96 risk; a better fill reduces it.

The general formula and the other caps on share count are in Position sizing.

Partial fills: decide before, not during

A partial fill leaves you with a different trade from the one you planned. Write the response into the plan:

• Keep the partial and do not chase. Path B. The position is smaller than planned, and so are both the risk and the reward.
• Chase with a second order. If Path B had chased the missing 400 shares with a market order at $3.24, the average entry would be $3.18, above the ceiling, and the risk per share wider than planned. That is the decision the ceiling was meant to prevent.
• Match the protective order to the filled shares. A stop for 800 shares on a 400-share position can open an unintended short if it triggers. The DAS course lesson Orders, fills and protection are separate states shows how one platform tracks this.

Time in force for scalps

Time in force (TIF) decides what happens to the unfilled part.

• IOC (immediate or cancel): fills what it can now and cancels the rest. Nothing rests in the book.
• DAY: the unfilled part rests as a bid at your ceiling. That bid can fill minutes later, when price falls back through it, which is often the moment the idea has already failed.

For premarket orders, many brokers accept limit orders only, and some require a specific extended-hours TIF; Premarket scalping covers those conditions. The DAS course lesson Order types, routes, prices and TIF shows how one platform writes these fields.

Around halts and LULD bands

Under the LULD Plan, trades cannot execute outside a stock's price bands. How a venue handles a buy limit priced above the upper band (repricing it, holding it or rejecting it) depends on the venue and on your broker, so read your broker's documentation rather than assuming. During a halt, an order may be held for the reopening or cancelled, again depending on the broker. If an order does take part in a reopening, the ceiling is the one thing limiting your price: a market order in the same reopening has no limit at all. The US Day Trading Fundamentals lesson What happens to your orders during a halt and FennEdge's LULD article cover the rules.

Observe vs. infer

At 10:02:15 ET in the Teasel Robotics example (fictional; all figures Illustrative):

Odds box

Whether those 1.2 cents are worth it depends on what the missed and partial orders would have done. If misses cluster on the trades that ran (as in Paths B and C), a tight ceiling quietly removes many of your best outcomes from the sample. If misses are random, the tighter ceiling saves money. That is a question for your own log.

What shifts the odds

These are hypotheses to record, not findings; no FennEdge sample links them to fill outcomes yet:

• Ceiling offset relative to the spread and to your target.
• Displayed size up to the ceiling compared with your order size.
• Speed of the quote: how many times the ask changed in the last few seconds.
• Latency: time from your decision to the order reaching the venue, including any confirmation step.
• Time of day and session: the open and the premarket tend to have thinner books.
• Order size relative to recent one-minute volume.

Cost of being wrong

Teasel Robotics plan, 1R = $96 (Illustrative). Each order outcome is shown with the move that works (target $3.31) and the move that fails (stop $3.05, filled at $3.04):

Chasing turned the partial fill into the worst stop outcome on the table: more shares at a worse price than the plan allowed.

How many trades before this means anything

Comparing two ceilings is a comparison of two proportions, and both are noisy. Suppose ask + $0.05 fills fully on 16 of 20 orders (80%) and ask + $0.01 on 11 of 20 (55%). The 95% Wilson intervals are about 58%–92% and 34%–74%: they overlap (computed on these hypothetical counts). At 100 orders each with the same rates, the intervals narrow to about 71%–87% and 45%–64%. A difference in fill rate also says nothing yet about R after costs; log both. How many trades before your numbers mean anything covers the method.

What this lesson does not claim

• It does not claim that any ceiling is correct for all stocks. The offsets and splits above are Illustrative.
• It does not claim marketable limits remove slippage. They cap it, and replace it with fill risk.
• Order handling around halts, LULD bands and premarket sessions differs by broker and venue; this lesson describes the questions to ask, not your broker's answer.
• Teasel Robotics and every price in this lesson are fictional.

Go deeper

• FennEdge first.
  • DAS course: Order types, routes, prices and TIF and Load, inspect, then understand Send, for how one platform builds a limit order before sending it.
  • The planned DAS Hotkey Script Builder at /tools/das-hotkey-builder (not live as of 2026-10-05) is designed to generate entry scripts with a limit at the ask plus an offset (bid minus an offset for shorts) and risk-based share counts, in your browser. Its scripts had not yet been run in a DAS client, so test them in a simulator account before any live use.
  • FennEdge article: Market, limit and stop orders.
• Market orders converted to limits. Some brokers convert market orders into limit orders with a price collar. Ask yours whether it does and how wide the collar is.
• IOC vs. FOK. Fill-or-kill orders fill completely or not at all; useful when a partial fill would be worse than none.
• Hotkeys. A marketable limit is a common hotkey entry; Hotkeys for day trading covers the safeguards.
• Simulators. Many simulators fill marketable limits at the arrival ask regardless of size. Paper trading covers how to correct for that.

Exercises

Six exercises follow this lesson: three concept checks, one calculation (share count from the ceiling), one scenario (choose a ceiling for two different books), and one practice task. Exercises, answers and progress are available after signing in.

Practice task: compare two ceilings. In a simulator, send 20 marketable limit entries, 10 with a ceiling of ask + 1 cent and 10 with ask + 5 cents (or two offsets that suit your stocks), alternating so both see similar conditions. For each order record the arrival quote, ceiling, shares requested, shares filled, average fill and what price did over the next two minutes, using the FennEdge practice log: download the practice log (CSV), with a column guide. Size every order from its ceiling. Log the orders that did not fill as well. Keep the log separate from the Trading Journal, which holds only real broker-synced trades.

Primary sources

• SEC. 17 CFR 242.600, Regulation NMS definitions (including "marketable limit order").
• FINRA. Types of orders.
• FINRA. Time parameters and qualifiers for stock orders.
• LULD Plan. Limit Up-Limit Down Plan.

Sources checked 2026-10-05. Teasel Robotics and all prices, books, fills, fill-rate splits and costs in this lesson are fictional and Illustrative. This lesson is education, not a recommendation to buy or sell any security. Past patterns do not indicate future results.