A Strange Thing Beginners Notice
You buy an asset, the price does not move, but your account immediately shows a loss.
Often, the platform is not wrong. You simply crossed the bid-ask spread.
Bid, Ask, and Last Price Are Different
| Term | Meaning |
|---|---|
| Bid | Highest price buyers are currently willing to pay |
| Ask | Lowest price sellers are currently willing to accept |
| Last | Most recent executed trade price |
If the bid is 9.90, the ask is 10.10, and the last price is 10.00, a market buy may fill near 10.10.
If you immediately sell, you may only receive around 9.90.
That 0.20 gap is a cost that existed before your trade.
Why Does the Spread Exist?
The bid-ask spread compensates liquidity providers for uncertainty.
Market makers and sellers provide liquidity, but they take price risk, inventory risk, and information risk. The thinner the market, the wider the compensation usually becomes.
The spread is not just a decimal. It is money you pay when entering and exiting a market.
How to Judge Whether the Spread Is Expensive
Use the spread as a percentage of the mid price. The mid price sits between the bid and ask:
Spread % = (Ask - Bid) / Mid Price
Example:
Bid 99.95, Ask 100.05
Spread 0.10, Mid 100.00
Spread % = 0.10%
For short-term trading, even 0.10% is not always small. In thin tokens, small stocks, or event contracts, spreads can reach 1%–5%.
30-Second Pre-Trade Check
- How wide is the bid-ask spread?
- Is the spread larger than your expected edge?
- Is order book depth sufficient?
- Is this a quiet trading window?
- Can you wait with a limit order?
If the spread already destroys your trade idea, do not force the trade just to be filled immediately.
Quiz
Q1. Is the last price always your fill price?
A. Yes B. No
Q2. What is the bid-ask spread?
A. A hidden execution cost B. A fixed tax C. A dividend D. Guaranteed return
Q3. If the spread is wide, what is safer?
A. Rush with a market order B. Check depth and use a limit order
C. Ignore price D. Add leverage
Answer Key
Q1: B Q2: A Q3: B
Further reading: Investopedia — Bid-Ask Spread · Nasdaq — Bid and Ask
For education only. Always check price, depth, and costs before trading.
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