Every wave of stock-market debuts — and 2025 and 2026 have brought plenty — comes with a hidden clock. It's called the lock-up, and understanding it explains a lot about how a freshly public stock behaves in its first year.
What a lock-up is
When a company holds an initial public offering (IPO) — its first sale of shares to the public — the banks underwriting the deal require the company's insiders to sign a lock-up agreement. It's a contractual promise not to sell their shares for a set stretch after the debut, as the SEC explains in its guidance for IPO investors. The freeze typically runs 90 to 180 days, though terms vary.
"Insiders" here is broad: founders, executives, board members, employees who hold stock, and the venture-capital and private-equity investors who backed the company before it went public. Between them they often own the bulk of the shares — so the lock-up keeps most of the company off the market at first.
Why it exists
The logic is supply and demand. Picture insiders free to sell the morning after an IPO: a flood of shares hits a market that has only just set a price, demand is overwhelmed, and the stock tumbles — leaving the public buyers who just bought in nursing losses.
Lock-ups prevent that. They give a new stock time to find a stable price, and they signal confidence — insiders agreeing to hold, rather than cash out immediately, suggests they believe in the company's longer-term value. For underwriters, the lock-up is a standard tool to protect the deal and reassure buyers.
What happens when the lock-up expires
The expiration date is when the restriction lifts and insiders are legally free to sell. It matters because a large block of shares can suddenly become tradable at once. The stock's "float" — the number of shares available to the public — can jump sharply. If thousands of insiders' shares were sidelined, expiry puts them all back in play.
Does that mean the stock always falls? No. Markets look ahead, and lock-up dates are known in advance — disclosed in the company's IPO prospectus (the S-1, its registration document filed with the SEC). Some stocks drift lower in the run-up as traders anticipate the extra supply; others absorb the selling with little effect. Market studies have long noted that lock-up expirations tend to coincide with modest average price dips, but the range of outcomes is wide and depends on the company's results and the mood of the market. Treat it as a known event to watch, not a guaranteed sell-off.
Not everyone rushes for the exit
A crucial nuance: insiders selling after a lock-up are frequently doing so on autopilot. Many sell under Rule 10b5-1 plans — pre-arranged schedules, adopted when the insider has no inside information, that sell a set number of shares at set times, as the SEC's investor glossary describes. Because the plan is fixed in advance, the sales proceed mechanically regardless of the day's news, which is precisely the point — it shields insiders from accusations of trading on secret information.
Companies also vary the mechanics: some negotiate early or staggered releases so that not every share unlocks on a single day, softening the impact.
What it means for an ordinary investor
If you own or are eyeing a recently public company, the lock-up expiration date is worth knowing — it's public, sitting in the prospectus and IPO disclosures. A large unlock can bring short-term volatility.
But don't read insider selling as an automatic red flag. Founders and early employees sell for ordinary reasons — buying a home, diversifying wealth that's almost entirely tied up in one stock, funding a new venture — and much of it is scheduled long in advance. What matters far more is whether the underlying business is delivering. Boursel gives no investment advice; the sensible posture is to know when the freeze thaws, expect some noise around it, and keep your eyes on fundamentals rather than the sale itself.
