Two traders look at the same option chain. One buys an ATM strike quoting Rs 120 to sell and Rs 121 to buy. The other buys a far OTM strike quoting Rs 28 to sell and Rs 35 to buy, because it looks cheaper and lets them buy more lots. On paper, the second trader got more exposure for less money. In practice, they just paid a hidden cost of Rs 7 per unit before the trade even had a chance to move in their favour. That gap between the two prices is the bid-ask spread, and it is one of the most overlooked numbers on the entire option chain.

This builds directly on our guide on how to read an option chain, where the bid and ask columns were introduced. Here, we go deeper into what that gap actually costs you and why it varies so much from strike to strike.

What Bid and Ask Actually Represent

The bid price is the highest price a buyer is currently willing to pay for an option. The ask price, sometimes called the offer, is the lowest price a seller is currently willing to accept. Whenever you place a market order to buy, you get filled at the ask. Whenever you sell, you get filled at the bid. The bid-ask spread is simply the difference between these two numbers, and it exists because market makers and other participants need some margin to compensate for the risk of holding a position and providing continuous liquidity.

Why the Spread Matters More Than Beginners Realize

Every time you enter and exit a position using market orders, you effectively cross this spread twice, once buying at the ask and once selling at the bid. On a Nifty option with a lot size of 75, a spread of just Rs 2 costs you Rs 150 per lot round trip, purely from the spread itself, before accounting for brokerage or any actual adverse price movement. Widen that spread to Rs 8 or Rs 10, common on illiquid strikes, and that cost jumps to Rs 600 to 750 per lot, an amount that can quietly eat a large chunk of a small trade's potential profit.

Why Some Strikes Have Tight Spreads and Others Do Not

Spread width is not random. It comes down almost entirely to liquidity, which itself depends on how many market participants are actively trading a specific strike.

Distance from the current market price. ATM and near-the-money strikes, as covered in our guide to choosing the right strike price, see the highest trading activity, since most retail and institutional flow concentrates around spot. This naturally keeps their spreads tight. Strikes far in the money or far out of the money see far less activity, and market makers widen the spread to compensate for the added risk of holding a position that fewer people are trading.

Open interest at that strike. A strike with high open interest, covered in our detailed breakdown of open interest, usually also carries tighter spreads, since a large outstanding position count generally reflects active, ongoing participant interest rather than a strike that only got touched once and was forgotten.

Time to expiry. Spreads tend to widen as expiry approaches for strikes that are deep in or out of the money, since fewer participants want to hold positions with rapidly eroding time value in illiquid contracts.

Underlying instrument itself. Nifty and Bank Nifty options are, by a wide margin, the most liquid contracts on NSE. Move to an individual stock's options, and spreads widen considerably even at the ATM strike, simply because far fewer traders are active in most single stock options compared to the index.

Liquid vs Illiquid Strikes at a Glance

Factor	Liquid Strike (e.g. Nifty ATM)	Illiquid Strike (e.g. deep OTM or far month)
Typical bid-ask spread	Re 1 to Rs 2	Rs 5 to Rs 15 or more
Open interest	High	Low
Ease of exit	Fast, minimal slippage	Slow, may need to accept a worse price
Best suited for	Active intraday and short-term trades	Generally best avoided unless holding to expiry

How to Actually Check Liquidity Before Trading

Before placing an order, glance at three things on the option chain together rather than just the premium. First, the spread itself between bid and ask. Second, the open interest at that strike relative to neighbouring strikes. Third, the day's traded volume so far. A strike showing a tight spread, healthy open interest, and steady volume is genuinely liquid. A strike showing a wide spread with low open interest and barely any volume, even if its premium looks attractively cheap, is a strike where getting out quickly at a fair price may prove difficult.

This becomes especially important during high volatility weeks, when spreads across the board tend to widen further as market makers price in additional uncertainty, a dynamic worth factoring into any of the setups covered in strategies built for high volatility weeks.

The Trap of Chasing Cheap, Illiquid Options

A recurring pattern among newer options traders is picking the cheapest available strike without checking its spread or open interest, only to discover that exiting the position, especially in a hurry during a fast market move, means selling well below the last traded price simply because there is no one on the other side willing to pay a fair price. This is a slippage cost that never shows up in a backtest or a strategy explanation, but it shows up very clearly in your actual trading account. It ties into the same broader gap between understanding market mechanics and trading them profitably, explored in why most retail traders in India end up losing money in the stock market.

Factoring in spread cost is also part of proper risk management, since a trade plan built around the 3-5-7 rule for managing risk per trade only works if your actual entry and exit prices are close to what you planned for, which a wide, illiquid spread can quietly undermine even when your market view turns out to be correct.

Disclaimer: This article is for educational purposes only and does not constitute investment or trading advice. Bid-ask spread figures used here are illustrative examples and not live market quotes. Options trading carries a high degree of risk and is not suitable for every investor. Please read all related documents carefully and consult a SEBI-registered advisor before trading in the F&O segment.

Frequently Asked Questions (FAQ)

1. What is the bid-ask spread in an option chain?

The bid-ask spread is the difference between the highest price buyers are willing to pay and the lowest price sellers are willing to accept for an option.

2. Why do some option strikes have wider spreads than others?

Strikes far from the current market price or with low open interest typically see less trading activity, leading market makers to quote wider spreads to compensate for reduced liquidity.

3. How does a wide bid-ask spread affect my trade?

A wide spread increases your effective cost of entering and exiting a position, since you buy at the higher ask price and sell at the lower bid price.

4. Are Nifty options more liquid than stock options?

Yes, Nifty and Bank Nifty options are generally far more liquid than most individual stock options, resulting in tighter bid-ask spreads.

5. How can I check if an option strike is liquid before trading?

Check the bid-ask spread, open interest, and traded volume together. Tight spreads with healthy open interest and volume indicate genuine liquidity.