Trade From Quote To Fill
This conversation was generated using Cook'd AI's career assistant and reviewed by Fallon Han from our editorial team for accuracy.
I'm a senior political science student in the UK aiming for sales and trading in London on a graduate visa. Can you explain how a simple trade goes from a quote to an executed price in a fast market?
Yes. Start with the quote: a market maker or exchange shows a bid and ask, which is the current price to sell or buy. If you send a market order, you are asking to trade immediately against the best available quote. In a fast market, that quote can change before your order reaches the book, so the executed price may differ from what you saw. That gap is mainly about liquidity and speed. If there is plenty of depth, your order clears close to the displayed price. If liquidity is thin or the market is moving, your order can sweep through several price levels and get a worse fill.
So the spread is basically the cost of trading fast? And why do limit orders and market orders behave so differently when volatility spikes?
Exactly, the bid ask spread is one visible part of trading cost. A tighter spread usually means better liquidity and lower immediate cost. Market orders prioritize certainty of execution, so in volatility they can suffer slippage because you accept the best available price, not a guaranteed price. Limit orders do the opposite: they protect price, but you may not get filled if the market moves away. In a fast tape, market participants often widen spreads because they are less willing to be picked off, which makes market orders more expensive and limit orders harder to execute.
If liquidity is just the ability to trade without moving the price much, how do I think about order book depth versus spread when a stock is suddenly hit by news?
Think of them together. Spread tells you the immediate cost at the top of the book, while depth tells you how much volume sits at each price level behind it. On a news shock, spreads often widen first because uncertainty rises. Then depth thins as resting limit orders get pulled. If you send a size order into that environment, the first few shares might trade near the displayed quote, but the rest can consume deeper levels and move the price sharply. For interviews, say that liquidity is not just narrow spread, it is also stable depth and resilience after a shock.
What order type would a trader use if they wanted to avoid getting terrible slippage but still needed to get something done quickly?
A common answer is a limit order with urgency management, or a marketable limit order. That means you set a worst acceptable price, but make it close enough to the touch that it should execute quickly if liquidity is there. It gives more control than a pure market order. Traders also split size into smaller clips to reduce market impact. In a fast market, the choice is usually between execution certainty, price certainty, and speed. The best order type depends on which of those matters most for the desk's objective.
How would I explain this cleanly in an interview if they ask why a quote changed between when I clicked and when it filled?
You can say: the displayed quote was only a snapshot, and in a fast market the order book can update before execution. My order interacted with the available liquidity at the time it reached the market, so the fill reflected the live book, not the stale screen price. Then add that wider spreads, thinner depth, and aggressive order flow all increase slippage. That shows you understand microstructure, not just the headline idea of supply and demand.