Bid-Ask Spread
The bid-ask spread is the difference between the highest price a buyer is currently willing to pay for a stock (the bid) and the lowest price a seller is willing to accept (the ask). It is the toll every investor pays for immediate execution, and it never shows up on a statement as a fee.
The math
Take a stock quoted at $50.00 bid, $50.10 ask. The spread is $0.10, or 0.2% of the price.
Buy 1,000 shares at the ask and you pay $50,100. Turn around and sell instantly at the bid and you collect only $50,000.
| Buy at the ask | Sell at the bid | |
|---|---|---|
| Price | $50.10 | $50.00 |
| 1,000 shares | $50,100 | $50,000 |
| Round-trip cost | $100 |
On a large-cap name the spread might be a penny; on a thinly traded small cap it can run 1% or more, turning the same round trip into $500 or $1,000.
The trap
Investors screen for commission-free brokers, then hand back multiples of any commission through wide spreads on illiquid names. The damage compounds with activity: someone rebalancing a small-cap portfolio monthly through 1% spreads gives up roughly 12% a year to market makers, a drag few ever measure because it hides inside execution prices.
The move
A long-term stock picker checks the spread before sizing any position, especially below $2 billion in market capitalization. A practical reflex: pull up the quote, compute spread divided by price, and treat anything above 0.5% as a real cost that the investment thesis must overcome.
Since buy-and-hold investing means few trades, each one deserves a limit order placed inside the spread rather than a market order that pays the full toll. Patience is an edge here; the investor who can wait a day for a fill keeps money the impatient trader donates.