Imagine you are finalizing a ‘Buy’ recommendation for a mid-cap stock that appears undervalued based on your DCF model. You have verified its turnover ratios, which look acceptable, and you are ready to present the case to your investment committee. However, when you attempt to simulate a bulk order of 50,000 shares, you notice that the bid-ask spread widens significantly as your simulated order hits the order book. This phenomenon, where the act of trading itself shifts the market price against you, is known as impact cost.
Impact cost represents the percentage deviation from the ideal price—usually the average of the best bid and ask—that an investor pays when executing a large transaction. In the Indian equity markets, liquidity is not merely the number of shares changing hands; it is the ability to absorb size without price distortion.
Even if a stock shows high daily trading volume, it may suffer from ’thin’ order books where a large buy order consumes all available sell limit orders, forcing the buyer to climb up the price ladder to get the order filled.
As a research analyst, you must recognize that impact cost is the true measure of your execution risk. If your client manages a large corpus and needs to build a position in a mid-cap stock, a high impact cost can erode the alpha you expect to generate. For instance, if you project a 15% upside but the impact cost of entry and subsequent exit totals 3%, your realized return is effectively dampened. You must compare the expected transaction cost against the potential return of your recommendation.
In your valuation reports, always consider the ’liquidity-adjusted return.’ If two stocks offer similar upside, the one with lower impact cost—and therefore higher liquidity—is qualitatively superior for institutional portfolios. Never assume that a liquid-looking stock will remain so during periods of market stress or high volatility, as order books often evaporate exactly when liquidity is needed most. Your job is to ensure that the client’s investment horizon and capital size align with the stock’s ability to facilitate entry and exit without creating a self-inflicted price shock.
Nuance
Check Your Understanding
An analyst intends to execute a large buy order for a stock. The ‘ideal price’ is INR 500 (the average of the best bid and ask). The order is executed at an average price of INR 505. What is the impact cost?
Which of the following scenarios best illustrates the risk of high impact cost for a portfolio manager?
This is a companion read for Section 12.12 — Measuring liquidity of equity shares from PASS Research Analyst Certification Examination by Akhilesh Gururani, available on Amazon Kindle.
Copyright © 2026 Akhilesh Gururani. All rights reserved.