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Limit orders: price control, no guarantee

Lesson 9 · about 8 min

A limit order is the opposite trade-off to a market order. You name your price. In exchange, you accept that you might not get filled at all. Most experienced traders use limit orders for almost every entry, and once you understand why, you probably will too.

What a limit order says

"Buy this many at this price or better." Or: "Sell this many at this price or better."

For a buy limit, "or better" means lower. For a sell limit, it means higher. So:

  • A buy limit at 50.00 fills at 50.00 or anything below it. It will not fill at 50.01.
  • A sell limit at 52.00 fills at 52.00 or anything above it. It will not fill at 51.99.

If the market is currently 50.10 bid, 50.12 ask, and you place a buy limit at 50.00, your order sits in the book below the current bid and waits. If someone sells enough to push the price down through 50.00, you get filled. If the price never comes back, you never buy. That is the deal.

Marketable limit orders

Here is the trick most beginners miss. A limit order does not have to sit and wait. If you place a buy limit at or above the current ask, it fills immediately, just like a market order, but with a ceiling.

Market: 50.10 bid, 50.12 ask. You place a buy limit at 50.15.

  • The order fills right away at 50.12, the best available price (you do not pay 50.15 just because you said 50.15; you get the ask).
  • If the book is thin and 50.12 has only 100 shares, the rest fills at 50.13, 50.14, 50.15, and then stops. Anything that would have cost more than 50.15 is left unfilled.

This is called a marketable limit order and it is what professionals mean when they say "never use market orders". You get the speed of a market order and a hard cap on the damage. The only cost is that in a fast market you might get a partial fill, which is nearly always better than a full fill at a stupid price.

Resting limit orders: being the maker

When your limit order sits in the book waiting, you have become a liquidity provider. You are the bid (or the ask) that someone else's market order will hit. Two consequences:

  1. You capture the spread instead of paying it. If you buy at the bid instead of the ask, you save the spread on entry. Over hundreds of trades this is a meaningful edge.
  2. You only get filled when someone wants to sell to you. In a rising market, your buy limit below the price may never fill; you "miss the move". In a falling market, it will fill, and then the price may keep falling. Resting limit orders have a built-in bias: they fill when the short-term flow is going against you.

That second point is not a reason to avoid them; it is a reason to place them where you would actually want to own the asset, not just a few cents below the price to save a few cents.

Partial fills

If you place a limit buy for 1,000 shares and only 400 are available at your price, you get 400 and the remaining 600 stay open. Most brokers show this as "partially filled". You can cancel the rest or leave it. Be aware that some brokers charge a commission per fill, so one 1,000-share order filled in ten pieces can cost ten commissions. Check.

Where limit orders are essential

Product Why limit orders matter
Options Spreads are wide; a limit at the mid often fills and saves several percent
Small caps Books are thin; a market order can walk 2-5%
Extended hours Often the only order type allowed
Crypto altcoins Thin books, big spreads, no regulator
Futures outside the front month Low liquidity
Entering any position at a specific level You want that price, not "around there"

In options specifically, a good habit is to place a limit at the mid-point between bid and ask, wait a few seconds, and then adjust by a cent or two toward the market if you are not filled. You will pay far less than a market order and almost always get done.

Key idea: A limit order caps what you pay or floors what you receive. A marketable limit order gives you the immediacy of a market order with a hard limit on slippage, which is why it should be your default.

Common mistakes

  • Placing a buy limit above the ask by a lot "to make sure it fills". It will fill, at the ask, but if the book is thin you have just authorized walking it up to your limit. Cap it a tick or two above the ask, not a dollar.
  • Setting the limit too far away to save a few cents, then watching the trade run without you. If the setup is good, a few cents is not the point.
  • Forgetting the order is still open. A day-only limit cancels at the close; a good-till-cancelled limit can sit for weeks and fill on a random Tuesday when you have forgotten why you wanted it. More on time-in-force in the last lesson of this module.
  • Confusing a limit with a stop. A buy limit is below the current price and waits for a dip. A buy stop is above it and waits for a breakout. Placing a "buy limit" above the ask when you meant a stop will just fill you immediately at the ask.

Try it: On a paper account, place three buy orders in the same liquid stock: a market order, a limit one cent above the ask, and a limit five cents below the bid. Note which fill, at what price, and how long the third one takes (if it fills at all). You have just experienced the entire trade-off in one exercise.

Recap

  • A limit order fills only at your price or better; it may not fill at all.
  • A limit at or through the current ask/bid fills immediately with a cap on slippage; this "marketable limit" should be your default entry.
  • Resting limit orders capture the spread but tend to fill when short-term flow is against you.
  • Limit orders are essential in options, small caps, extended hours and thin crypto.
  • Watch for partial fills, forgotten open orders, and mixing up limits with stops.

See it drawn

Original diagrams for the ideas on this page. Illustrative, not real market data.

Market, limit and stop ordersA price track crossing a resting limit order below the market and a stop order above it.10410210098PriceTime (the market moves left to right)priceSTOP BUY at 103.00waits above the market; becomes a market order when touchedtriggers hereMARKET ORDERfills at once at 100.60filled hereLIMIT BUY at 98.50rests below; fills only at 98.50 or better
Market, limit and stop orders. A market order buys straight away at whatever price is there. A limit order waits below until the price comes to it, and a stop order sits above and turns into a market order the moment price touches it.
Bid-ask spread in an order bookSell orders stacked above buy orders with a gap between the best of each.SELLERS (asks)50.0690050.051,40050.0460050.011,10050.002,30049.99800spread = 0.03BUYERS (bids)
The bid-ask spread. Buy orders sit below, sell orders above, and the gap between the best bid (50.01) and best ask (50.04) is the spread you pay to cross. Bar length shows the size resting at each price.
Slippage on a market orderA buy order clears four price levels, so the average price paid is worse than the price first quoted.Buy 1,000 shares at marketpricesell orders resting (bar length = size)20.04300 shares20.03200 shares20.01200 shares20.00300 sharesnothing resting at 20.02order sweeps up the bookaverage fill 20.02SLIPPAGE0.02 a share$20.00 in totalintended 20.00Each level fills at its own price; the average is what you really paid.
Slippage on a market order. You click at 20.00, but only 300 shares are resting there, so the rest of the order fills at 20.01, 20.03 and 20.04. The average price paid is 20.02, and that two-cent gap is slippage.