What Is Bid-Ask Spread? A Beginner's Guide to Option and Stock Trading
Learn what the bid price, ask price, and bid-ask spread mean, why spreads matter, and how liquidity can affect the cost of entering and exiting trades.
What Is a Bid-Ask Spread?
The bid-ask spread is the difference between the highest price a buyer is currently willing to pay and the lowest price a seller is currently willing to accept.
For example, if an option has a bid of ₹120 and an ask of ₹123, the bid-ask spread is ₹3.
The spread is an important part of trading because it can affect the effective cost of entering and exiting a position.
What Is the Bid Price?
The bid price represents the highest currently quoted price at which a buyer is willing to purchase the security or option.
If you want to sell immediately, the bid is generally the price available to you, subject to market conditions and available quantity.
What Is the Ask Price?
The ask price represents the lowest currently quoted price at which a seller is willing to sell.
If you want to buy immediately, the ask is generally the price you would look at first.
How Is the Bid-Ask Spread Calculated?
The basic formula is:
Bid-Ask Spread = Ask Price − Bid Price
For example:
| Bid | Ask | Spread |
|---:|---:|---:|
| ₹98 | ₹99 | ₹1 |
| ₹100 | ₹103 | ₹3 |
| ₹145 | ₹152 | ₹7 |
A smaller spread generally means buyers and sellers are closer together in their current quotes.
Why Does the Bid-Ask Spread Matter?
The spread matters because the price you see is not necessarily the price at which you can immediately buy and sell.
Suppose an option shows a bid of ₹100 and an ask of ₹104.
A trader buying immediately may pay around ₹104, while a trader selling immediately may receive around ₹100.
The ₹4 difference represents trading friction between the two sides of the market.
Bid-Ask Spread in Options
Bid-ask spreads can vary significantly between different option contracts.
An ATM option with substantial trading activity may have a relatively narrow spread, while a far OTM option with limited activity may have a wider spread.
When analysing an option chain, bid and ask prices should therefore be considered alongside volume and Open Interest.
See What Is an Option Chain? A Beginner's Guide to Reading the Options Chain.
Bid-Ask Spread and Liquidity
Liquidity refers to how easily a security or option can be bought or sold without causing a significant price impact.
Liquid contracts often have more active buyers and sellers and tighter bid-ask spreads.
Less liquid contracts can have wider spreads and may be more difficult to execute efficiently.
Learn more in What Is Liquidity in the Stock Market?.
Bid-Ask Spread vs Option Premium
The bid-ask spread is not the same as the option premium.
The option premium is the price of the option.
The bid-ask spread is the difference between the current bid and ask quotations for that option.
For the fundamentals of option pricing, read What Is Option Premium? A Beginner's Guide to Option Pricing.
Bid-Ask Spread and Market Orders
A market order prioritises execution rather than a specific price.
When using a market order in a contract with a wide spread, the execution price can be less favourable than expected.
This is why understanding the spread is especially important when trading options with lower liquidity.
Bid-Ask Spread and Limit Orders
A limit order allows a trader to specify the maximum price they are willing to pay when buying or the minimum price they are willing to accept when selling.
A limit order can provide greater price control, although there is no guarantee that it will be executed.
What Causes a Wide Bid-Ask Spread?
Several factors can contribute to a wider spread:
Spreads can also change rapidly as market conditions change.
How Beginners Can Use the Bid-Ask Spread
Before entering an option trade, check:
Do not judge liquidity using only one metric.
Simple Example
Suppose you want to buy an option.
Bid = ₹210
Ask = ₹214
Therefore:
Spread = ₹214 − ₹210 = ₹4
If you immediately buy at the ask and later sell at the bid without any change in the underlying or option value, the spread alone creates a ₹4 difference per option.
This illustrates why execution quality matters in options trading.
Final Thoughts
The bid-ask spread is a simple concept, but it is an important part of real-world trading.
Understanding the spread helps traders recognise the difference between an option's displayed premium and the prices at which buyers and sellers are currently willing to transact.
For options traders, studying the spread alongside liquidity, volume, Open Interest, and option premium provides a more complete view of execution conditions.
Disclaimer
This article is for educational purposes only and does not constitute financial advice. Please consult a SEBI registered investment advisor before making investment decisions. All investments carry risk.
This article is for educational purposes only and does not constitute financial advice. Please consult a SEBI registered investment advisor before making any investment decisions.