What is a Lockup Period and Why It Matters

When a company goes public, only a fraction of its total equity—typically 10% to 25%—is made available to the open market as the "free float." The remaining 75% to 90% is held by pre-IPO shareholders: founders, company executives, early angel backers, venture capitalists, and private equity firms.

A Lockup Agreement is a legally binding contract between these pre-IPO insiders and the lead underwriters prohibiting insiders from selling, hedging, or pledging their equity for a specified duration post-listing.

Why Lockup Agreements Exist

Without a mandatory restriction, early investors who bought equity at fractions of a cent could flood the public exchanges on day one to lock in massive windfalls. That supply avalanche could overwhelm buyer demand and trigger a sharp share price collapse. The lockup period preserves market balance, keeping early insiders invested alongside new public shareholders while the stock establishes an orderly trading history.

The Standard Duration and The Expiration "Cliff"

• The Baseline Window: Historically, the standard lockup length spans 180 calendar days following the IPO date, though shorter windows (90 or 120 days) and staged early releases have become more common, particularly in tech and biotech listings.
• The Expiration Cliff: On the day the lockup contract terminates, millions—sometimes hundreds of millions—of previously restricted shares can become tradable at once. If early venture capitalists and institutional sponsors choose to sell, the market faces a sudden increase in supply. Share prices often become more volatile around the expiration date, and some academic studies have found a modest average dip in the days around it, though the effect varies from deal to deal.

Fine-Print Lockup Variations to Monitor

Modern prospectuses often incorporate non-standard lockup language that alters the traditional 180-day countdown:

• Price-Triggered Early Releases: Provisions permitting a percentage of insider shares (e.g., 20% to 33%) to unlock early if the stock trades above a specified threshold (e.g., 125% to 150% of the IPO offer price) for 10 out of 15 consecutive trading sessions following an earnings release.
• Staggered / Tiered Releases: Tranches of shares unlocking in progressive waves (e.g., 25% after the first quarterly report, 25% after the second, and the remaining 50% at day 180).
• Employee vs. Sponsor Disparities: Filings where regular employee lockups expire weeks earlier or later than major institutional funds.

Tracking the lockup calendar is one of the most useful risk checks for an IPO investor: a lockup expiry can add a large amount of supply to the market, so it helps to know when it is coming.