Lock-Up Period

A lock-up period is a contractual restriction — agreed between the issuer, pre-IPO shareholders, and the underwriter — that prohibits certain existing shareholders from selling their shares in the open market for a defined period following the IPO. Covered parties typically include founders, co-founders, PE and VC investors, directors, officers, and any shareholder owning 5% or more of the company. The standard duration in the United States is 180 days from the IPO date, governed by FINRA Rule 5110 for underwriters but otherwise set contractually. In Korea, the KRX listing regulations mandate 6 months to 1 year of lock-up for major shareholders and PE sponsors, depending on the listing pathway and share class.

The rationale is straightforward: IPO investors are buying into a company with asymmetric information relative to insiders. If the founders or PE sponsors who backed the company through its formative years are legally free to dump all their shares on day one, the IPO market would essentially become a mechanism for insiders to exit at the expense of public investors. The lock-up agreement creates a credible commitment device: insiders must hold through the initial price discovery period, which aligns their interests with those of the new public shareholders. Underwriters enforce this contractually, and in Korea, the Korea Securities Depository (KSD) manages the mechanical trading restrictions on lock-up shares at the system level, preventing unauthorized sales.

The negotiation of lock-up terms is a meaningful part of the IPO structuring process. Shorter lock-ups benefit insiders who want liquidity sooner, while longer lock-ups signal confidence to IPO investors and can support a higher IPO valuation. High-growth technology companies, in particular, often use extended voluntary lock-up commitments as a marketing tool during roadshows — founders publicly pledging not to sell for two or three years beyond the contractual minimum. Conversely, for PE-backed IPOs where sponsors need to demonstrate a clear exit timeline to their own LPs, negotiating a shorter lock-up (or a phased release schedule) becomes a priority, sometimes at the cost of IPO pricing.

Lock-up expirations are treated as scheduled event risks by the ECM market. The magnitude of the overhang — defined as the number of lock-up shares eligible for sale relative to the existing daily trading volume or public float — determines how much downside pressure builds into the stock ahead of expiration. Academic studies of U.S. IPO markets consistently find that lock-up expirations are associated with abnormal returns of negative 1–3% in the week before expiration and an additional negative 3–5% around the expiration date itself, with the effect proportional to the size of the overhang. These patterns are well-known enough that most ECM desks maintain expiration calendars and begin flagging high-overhang names to their trading and research teams three to four weeks in advance.

The overhang is most severe when pre-IPO investors sitting on large unrealized gains have a firm incentive to sell immediately upon expiration. Consider a PE sponsor that invested in a company's pre-IPO round at ₩20,000 per share, while the IPO priced at ₩30,000 and the stock has since traded up to ₩45,000 by the lock-up expiration date. The PE fund has an IRR-driven mandate to return capital to LPs, and the premium to cost is too large to ignore. Market participants anticipating this dynamic begin shorting the stock or buying put options weeks before expiration, creating a self-fulfilling downward pressure even before a single share is sold. This is the mechanism by which overhang risk can become a tangible drag on stock performance well before the legal restriction expires.

However, not all lock-up expirations result in significant price declines. If the company's fundamentals are accelerating — beat-and-raise earnings reports, a transformative acquisition, or a product cycle inflection — the incremental selling pressure from insiders can be absorbed by new institutional demand. Alternatively, large PE sponsors frequently work with their IPO bookrunners to conduct a pre-arranged block trade or accelerated bookbuilding (ABB) in the two to four weeks before expiration. In an ABB, the bookrunner quietly canvasses institutional investors overnight, prices the block at a modest discount (typically 2–5%) to the prevailing market price, and places the entire lot in a single session. This technique converts what would have been a prolonged overhang into a single, well-anticipated event, after which the stock often recovers the discount within days.

The period surrounding lock-up expiration creates distinct strategic considerations for each class of market participant. For existing shareholders — PE sponsors, VC funds, and founding management — the primary decision is not whether to sell, but how to do so without self-destructing on market impact. A PE firm holding 20% of a ₩5 trillion market cap company cannot simply dump its entire position at the opening bell on expiration day; the market impact alone could reduce realized proceeds by 10–20% relative to pre-expiration prices. Sophisticated sellers therefore work with their banks months in advance to structure exit strategies: phased secondary offerings, ABBs timed to positive news flow, or SEC Rule 10b5-1 plans in the U.S. context, which allow insiders to pre-program automatic sales on a schedule established before they enter any material non-public information window.

Short sellers view high-overhang lock-up expirations as one of the cleanest tactical short opportunities in the equity market — a situation where the supply-demand imbalance is structurally foreseeable. However, this trade carries significant execution risks. First, if the overhang is well-publicized, the downside may be fully priced in weeks before expiration, leaving late shorts with no edge and substantial squeeze risk. Second, borrowing lock-up shares to facilitate a short often proves impossible or prohibitively expensive, since those shares are not in the lending pool. Third, management teams are acutely aware of the expiration calendar and sometimes time positive announcements — earnings beats, partnership deals, or guidance raises — to counteract selling pressure, which can catch shorts offside. The empirical evidence suggests that the best short entry is roughly three to four weeks before expiration, not on expiration day itself.

For long-only institutional investors, the post-expiration period can represent a compelling entry point once the overhang has been fully digested. After the lock-up shares are absorbed into the market, the free float increases materially, which has a second-order effect through index rebalancing. Index providers like MSCI and FTSE calculate constituent weights based on free-float-adjusted market cap; a larger float means a higher index weight, which triggers mandatory buying from passive funds tracking those benchmarks. In Korea, this dynamic is especially pronounced given the size of the passive AUM benchmarked to MSCI Korea and KOSPI 200. Several landmark Korean IPOs have followed a pattern of post-lock-up softness followed by a sharp recovery six to twelve months later, coinciding with index inclusion events or weight increases that generated billions of won in automatic index-driven demand.