cornerstone lock-up

A contractually mandated period during which cornerstone investors in an IPO are prohibited from selling their shares.

A cornerstone lock-up is a contractually mandated period during which cornerstone investors in an Initial Public Offering (IPO) are prohibited from selling their shares. Cornerstone investors are typically large institutional backers, such as sovereign wealth funds, mutual funds, or high-net-worth individuals, who commit to purchasing significant blocks of shares before the public offering is priced. In exchange for guaranteed allocations, they agree to hold these shares for a specified timeframe, commonly six months to a year, after the company begins trading on the public exchange. These lock-up agreements are designed to signal institutional confidence to retail and other public investors, demonstrating that sophisticated market participants are committed to the company for the medium-to-long term. By keeping a substantial portion of the company's equity off the market during the volatile early months of public trading, the lock-up prevents immediate downward price pressure that could arise from large-scale liquidations. For retail investors, tracking the expiration date of a cornerstone lock-up is critical. As the lock-up period nears its end, the market often anticipates a sudden increase in the supply of tradable shares, known as an equity overhang. If cornerstone investors choose to liquidate their positions to realize gains or reallocate capital, this concentrated selling volume can lead to a sharp decline in the stock price. Conversely, if the lock-up expires and these major institutions choose to maintain their holdings, it can serve as a positive signal of ongoing operational confidence.

Company A goes public with a total of 100 million shares outstanding. Three cornerstone investors purchase a combined 30 million shares (30% of the company) subject to a 6-month cornerstone lock-up. During the first 5 months, only the remaining 70 million shares are actively traded in the public float. As the 180-day lock-up expiration approaches, the market anticipates that the tradable float could suddenly increase by 42.8% (30 million / 70 million), causing the stock price to decline by 5% in the week leading up to the expiration date due to supply overhang fears.