What is a Limit Order? Definition, Formula, and Example
A limit order is an instruction to buy or sell a security only at a specified price or better, guaranteeing price but not execution.
Plain-English Definition
A limit order is a buy or sell instruction that executes only at your specified price or better — never worse. A buy limit at $150 fills at $150 or below; a sell limit at $150 fills at $150 or above. This is the opposite of a market order, which fills at whatever price is currently available. Limit orders guarantee price but sacrifice the certainty of execution: if the market never touches your price, the order expires unfilled.
How It Works
A limit order sits in the exchange's order book until one of three things happens:
1. The market reaches your limit price and there is sufficient contra-side liquidity to fill it
2. You cancel the order
3. The order's time-in-force expires (DAY, GTC, IOC, FOK)
Price-time priority governs execution: at a given price level, earlier orders fill first. A limit buy of 100 shares at $150.00 queued at 9:30:01 fills before an identical order queued at 9:30:02.
The core rule: Buy limit price ≤ current ask, Sell limit price ≥ current bid — otherwise the order becomes "marketable" and crosses the spread, filling immediately like a market order (but still capped at the limit price).
Worked Example
NVDA is quoted $485.20 bid × $485.35 ask. You believe $480 is a better entry.
You submit: BUY 100 NVDA LIMIT 480.00 DAY.
- If NVDA trades down and the ask drops to $480.00 or lower during market hours, your order fills.
- If NVDA rallies and never touches $480, the order expires at 4:00 PM ET unfilled.
- If NVDA gaps down to $475 at the open, your buy limit fills at $475 or better (price improvement) — not $480, because limit orders execute at the *limit price or better*.
Contrast with a market buy at the same moment: you'd pay $485.35 immediately, a $5.35 per-share premium over your target — $535 on 100 shares.
When Traders Use Limit Orders
- Entering positions at technical levels — support, moving averages (what is a moving average?), Fibonacci retracement zones
- Selling into resistance — sell limits placed at prior highs or overhead supply
- Avoiding slippage in thin stocks — market orders in illiquid names can fill cents or dollars away from quote
- Post-only liquidity provision — professional traders earn maker rebates by adding liquidity via limit orders
- Options trading — nearly all retail option fills should be limit orders due to wide bid-ask spreads
Limitations and Common Misconceptions
Non-execution risk is real. A limit order that never fills means you missed the move entirely. Traders who chronically set "cute" limit prices 1-2% below market often watch stocks rally without them.
Limit orders are not stop losses. A sell limit above the current price is a profit target, not downside protection. Protection requires a stop-loss order or stop-limit.
Partial fills happen. A 1,000-share limit order may fill 300 shares, then the market moves away. You now own a smaller position than intended with the remainder still working.
Price-time priority can hurt you. In fast markets, hidden iceberg orders or HFT queue-jumpers may fill ahead of you at your price, leaving your order behind when the level breaks.
Limit ≠ guarantee of the displayed price. In volatile opens, a stock can trade through your limit without filling every resting order at that level.