Trading · Orders and execution
Market vs limit orders: price certainty vs getting filled
When a market order or a limit order is the better tool, how marketable limits and partial fills work, and how to calculate slippage on a real order.
On this page
The market order and the limit order are the two building blocks of almost every trade. A market order says "fill me now." A limit order says "fill me only at this price or better." Every other order type, from stops to brackets, ends up sending one of these two to the market. Understanding the trade-off between them is the single most useful thing to know about placing orders.
This page goes beyond the one-line definitions. It shows how a market order actually meets the order book, why a limit order can sit at the right price and still not fill, what a "marketable limit" is and why many traders default to it, and how to put a dollar number on slippage before and after a trade. The examples are illustrative and use US market conventions as of 2026.
The core trade-off
The SEC's Investor.gov states the two sides plainly. A market order generally executes promptly, but the price is not guaranteed. A limit order executes only at your price or better, but execution is not guaranteed. You cannot have both certainties in one order. You decide which one matters more for this trade.
| Question | Market order | Limit order |
|---|---|---|
| Will it fill? | Almost always, in regular hours | Only if the market reaches your price |
| At what price? | Unknown until it fills | Your limit or better |
| Can it fill in pieces? | Yes, across several prices | Yes, at one or more prices within the limit |
| Accepted outside regular hours? | Usually not | Usually, if marked extended-hours |
| Biggest risk | Paying far more (or receiving less) | Missing the trade |
| Typical cost when it works | Half the spread, plus any book-walk | Little or none; may even earn the spread |
How a market order meets the book
The quote you see in an app shows only the top of the market: the best bid and the best ask, each with a size. Behind those prices sits a ladder of further offers at higher prices (and bids at lower ones). A market buy takes the best ask first. If the order is larger than the size shown there, it moves up to the next price level, then the next, until it is complete.
In practice it's often better than this picture. Brokers route most retail orders to wholesalers that frequently fill small market orders at or slightly inside the quote, and some liquidity is hidden from the displayed book. It can also be worse: quotes move in the milliseconds while your order travels, and displayed size can vanish when a large order appears. The ladder above is the mechanism, not a forecast.
How a limit order waits
A limit order that can't trade immediately rests until the market comes to it. Three things decide whether and when it fills.
Price. A buy limit at $19.95 cannot fill while the lowest ask is $20.00.
Time priority. On most venues, orders at the same price fill in the order they arrived. If 5,000 shares were bid at $19.95 before yours, those 5,000 shares generally need to trade before yours does. This is why a stock can "touch" your limit price on the chart without your order filling: the trades at that price may have used up the orders ahead of you.
Size. A seller may want to sell only 200 shares at your price, leaving the rest of your order unfilled.
Partial fills
A partial fill is common with limit orders and possible with market orders. You ask for 1,000 shares at $19.95 and get 300. The remaining 700 stay live until filled, canceled or expired at the end of the order's time-in-force. Two practical points follow:
- Costs. Most US brokers no longer charge stock commissions, but if yours charges per order, a fill spread over several days may count as several orders. Check the fee schedule.
- Position size. A partly filled entry leaves you with a different position than you planned. If you were going to place a stop based on 1,000 shares, you now hold 300.
An all-or-none instruction prevents partial fills, at the cost of being skipped over while smaller orders trade at your price.
The marketable limit order
A marketable limit order is a limit order priced to trade immediately: a buy limit at or above the current ask, or a sell limit at or below the current bid. It behaves like a market order while the quote stays put, but if the market jumps away, it stops at your limit instead of chasing.
Some brokers automatically add a price "collar" to market orders, converting them into limit orders a few percent away from the quote, to protect against extreme fills. The details differ by broker and are usually in the order-handling disclosures.
Calculating slippage
Slippage is the difference between the price you expected and the price you got, multiplied by the shares. "Expected" needs a definition. The most common benchmark for a single order is the arrival price: the midpoint of the bid and ask when you sent the order.
Measured this way, a market order in a liquid stock usually costs about half the spread. Round-trip, buying and later selling, it costs about one full spread plus any book-walk on each side. For a long-term investor buying a large, liquid fund once a month, that is trivial. For someone trading the same thinly traded stock several times a week, it can exceed every other cost.
When each order fits
Market orders fit when the stock is heavily traded, the spread is a cent or two, your order is small next to the quoted size, it's regular hours, and nothing is moving the price fast. They also fit when not trading is the bigger risk, for example exiting a position you've decided you must leave.
Limit orders fit when the spread is wide, the stock trades thinly, the order is large relative to quoted size, the market is not in its regular session, or the price is moving quickly around news. They're also the natural choice when you have a specific price in mind and are happy to wait.
Marketable limits fit in between: you want the trade now, but you want a ceiling in case the quote has moved by the time the order arrives.
Pitfalls
- Chasing a limit. Raising your buy limit a few cents at a time as the stock moves away often ends with a worse price than a single marketable limit would have given.
- Limit at the last trade price. The last trade can be stale. Set limits relative to the current bid and ask, not the last print.
- Forgetting resting orders. A forgotten limit order can fill weeks later in a very different market. Review open orders regularly.
- Assuming the chart shows every fill. A trade at your price on a chart doesn't mean your order was first in line at that price.
How Finabase helps
Finabase doesn't route orders; your broker does. But the quote page shows the live bid and ask with their sizes and the last trade's size, which is enough to estimate whether your order is small next to the quoted size, and how far a market order might walk. The same page shows the day's volume and average volume, and the screener can filter stocks by price and volume ranges, a quick way to spot names where limit orders are the safer default.
Frequently asked questions
Is a market order or a limit order better?
Neither is better in general. A market order is better when getting the trade done matters most and the stock is liquid. A limit order is better when price matters most, especially in thinly traded stocks, outside regular hours, or around news.
Why didn't my limit order fill when the stock hit my price?
Usually because other orders were ahead of yours at that price. Orders at the same price generally fill in the order they arrived, and the shares that traded at your price may all have gone to earlier orders. The price also has to be at or better than your limit: a buy at $50 needs a seller at $50.00 or lower.
What is a marketable limit order?
It's a limit order priced so it can trade right away: a buy limit at or above the current ask, or a sell limit at or below the current bid. It fills immediately like a market order but won't trade beyond your limit if the quote moves.
How much does a market order cost?
In a liquid stock, roughly half the bid-ask spread per share, compared with the midpoint. If your order is larger than the size quoted at the best price, add the extra cost of filling at the next price levels. Commissions, if your broker charges any, come on top.
Summary
Market orders buy certainty of execution and pay for it in price uncertainty: half the spread at best, and more when the order outruns the quoted size or the quote moves. Limit orders buy price certainty and pay for it in execution uncertainty: partial fills, late fills or no fill. Marketable limits combine immediacy with a ceiling. Measuring slippage against the midpoint when you send the order turns this from a matter of taste into a number you can check.