TL;DR: An initial public offering is a controlled, month-long process: the company files an S-1 registration statement with the SEC, hires underwriters to test demand with institutional investors on a roadshow, prices the deal the night before trading, and lists on an exchange the next morning. Underwriters keep a 15% greenshoe option to buy more shares at the offering price if demand overshoots, and insiders sign a lockup agreement—typically 180 days—that keeps them from dumping stock the day the shares hit the tape. Since 1980, U.S. IPOs have opened, on average, 19.0% above their offer price on the first day of trading, a phenomenon Jay Ritter’s dataset shows has been remarkably persistent across four decades.
Why companies go public in the first place
Going public is expensive, distracting, and permanently exposes management to quarterly scrutiny. Companies do it anyway for four reasons:
- Raise permanent capital. Selling new (primary) shares brings cash into the company—often to pay down debt, fund growth, or build a war chest for acquisitions.
- Provide an exit for early investors. Venture capital firms, private-equity owners, founders, and employees have illiquid stakes worth nothing until there’s a public market to sell into. An IPO creates that market.
- Give the company an acquisition currency. Public stock can be used as consideration in mergers instead of cash—far easier to price and much cheaper for the acquirer’s balance sheet.
- Brand and recruiting. Listed status confers legitimacy with customers, partners, and prospective hires who value tradable equity.
Analogy: taking a company public is like a musician moving from private house shows to a stadium tour. The revenue potential and reach explode, but so does the paperwork, the scrutiny, and the number of stakeholders whose expectations you now have to manage every 13 weeks.
Step 1: The S-1 filing
The IPO clock starts the day the company files a Form S-1 with the Securities and Exchange Commission. Under the Securities Act of 1933, companies cannot sell securities to the public without a registration statement declared “effective” by the SEC. The S-1 is that statement, and it is dense: risk factors, three years of audited financials, an MD&A section, capitalization, dilution math, use of proceeds, executive compensation, related-party transactions, and legal proceedings.
Two features of the S-1 that surprise first-time readers:
- The price range is a marketing tool, not a promise. A range like “$21–$25 per share” is set by the underwriters to test demand. Final pricing can land above, inside, below, or well outside that range. When Jersey Mike’s went public on July 30, 2026, it priced its IPO at $23 per share—the midpoint of its $21–$25 marketed range—and still opened at $21, below its own offering price.
- The S-1 is amended repeatedly. Every meaningful change (new financials, price-range update, share-count change) triggers an “S-1/A” filing. The final version used to sell the shares is typically called a Form 424B4 prospectus.
Since 2012, “emerging growth companies” (revenues under about $1.5B, adjusted for inflation) can file the S-1 confidentially under the JOBS Act, publicly disclosing it only about 15 days before the roadshow. That’s why you sometimes read “Company X has confidentially filed for an IPO”—the S-1 exists but the SEC’s public copy hasn’t dropped yet.
Step 2: The roadshow and bookbuilding
Once the SEC signals it will clear the deal, the company and its lead underwriters (called the “bookrunners”) spend roughly 7–10 business days on a roadshow—a whirlwind tour of one-on-one meetings and small-group presentations with mutual funds, hedge funds, sovereign wealth funds, and other large institutions. The pitch is standardized: management deck, growth story, financial model, Q&A.
During those meetings, the bookrunners are running a bookbuilding exercise. They ask each institution two questions:
- How many shares do you want?
- What price are you willing to pay?
The answers get logged in a running order book. When the book is done, the underwriters can see the demand curve: at $22, we can sell 50 million shares; at $24, only 25 million. That curve is what drives the final pricing decision.
Step 3: Pricing night
The night before the first day of trading, the underwriters, the company, and the lead bookrunners hold a “pricing meeting.” They pick a final offer price—the price at which shares are sold to the institutions in the book—and lock in the share count. The pricing decision is almost never “sell at the market-clearing price.” Underwriters routinely set the offer price below where they think the stock will open the next morning. That gap is called underpricing (or, less academically, “the pop”).
Why deliberately leave money on the table? Underwriters cite three reasons:
- Insurance against a broken deal. A day-one drop below the offer price is a PR disaster and damages the underwriter’s reputation for future mandates.
- Rewarding the institutions who agreed to hold. The largest allocations go to funds that promise not to flip. A first-day pop is their compensation.
- Marketing effect. A splashy first-day gain is free advertising for the stock and the underwriter’s league-table rank.
The academic literature on underpricing is enormous. The definitive dataset is maintained by Professor Jay Ritter at the University of Florida, who has tracked every U.S. IPO since 1980. His numbers:
| Period | Number of IPOs | Average first-day return | Money left on table* |
|---|---|---|---|
| 1980–1989 | 2,047 | 7.2% | $54 bn |
| 1990–1998 | 3,616 | 14.8% | $226 bn |
| 1999–2000 (dot-com bubble) | 856 | 64.6% | $129 bn |
| 2001–2025 | 2,824 | 19.1% | $790 bn |
| 1980–2025 total | 9,343 | 19.0% | $1,190 bn |
The 19.0% long-run average is arithmetic across every deal, big or small; the median deal is closer to 7%. And the tails are wild: in 2022, thanks to a handful of tiny microcap deals, mean first-day returns hit 48.9% on just 38 IPOs.
Step 4: The greenshoe (over-allotment option)
Buried in every prospectus is a clause called the greenshoe, or over-allotment option. It’s named after the Green Shoe Manufacturing Company, whose 1963 offering was the first to use one. Here’s how it works:
- The company grants the underwriters an option to buy an additional block of shares—typically 15% of the deal size—at the offering price, for a set window (usually 30–45 days after pricing).
- The underwriters actually oversell the deal by that same 15% on day one, going short. They now have a short position they need to cover.
- If the stock trades above the offer price, the underwriters exercise the greenshoe: the company issues the extra 15% of shares at the offer price, the underwriters cover their short, everyone gets more money. The company sees additional proceeds; the underwriters pocket their standard 7% gross spread on the extra volume; the stock has natural aftermarket demand.
- If the stock trades below the offer price, the underwriters cover their short by buying shares in the open market—which puts a bid under the stock exactly when it needs one. This is called price stabilization, is regulated under SEC Regulation M, and is explicitly disclosed in the prospectus.
The greenshoe is why you’ll read that Jersey Mike’s underwriters received “a 30-day option to purchase up to an additional 6,521,739 shares” in the deal’s pricing release—that’s 15% on top of the 43,478,261-share base deal, right on the market standard.
Step 5: The lockup agreement
By day one of trading, insiders—founders, executives, employees with vested equity, pre-IPO venture and PE investors—often hold the vast majority of the outstanding shares. If they were free to sell into the aftermarket, the float would balloon and the stock could crater. To prevent that, every large IPO includes a lockup agreement: a contract in which insiders promise not to sell, transfer, or hedge their shares for a set period after the offering.
Per the SEC’s investor bulletin on the topic, “most prevent insiders from selling their shares for 180 days,” and the terms have to be disclosed in the prospectus (Investor.gov, “Initial Public Offerings: Lockup Agreements”). Lockups are contracts between the insiders and the underwriters, not securities laws—which means the terms can be negotiated. Modern deals have gotten creative:
- Staggered releases. Rather than a cliff at day 180, some IPOs release insider shares in tranches. SpaceX’s 2026 IPO used a staggered lockup—its first tranche of roughly 20% of insider stock became eligible to trade on August 6, 2026, freeing up to 911.5 million shares against a June 12 IPO.
- Price-based early releases. Some agreements let insiders sell early if the stock trades above a specified price for a specified window (SpaceX’s had a 30% trigger over 5-of-10 days pre-earnings; the trigger didn’t hit).
- Quiet-period exceptions. Analyst-firm research quiet periods run 25 days after pricing under FINRA rules; that’s a separate constraint from the insider lockup and expires much sooner.
Traders watch lockup expiration dates closely because insider selling can meaningfully expand supply. Whether prices actually drop on the day is mixed empirically—in many high-profile cases the market prices the expected supply in ahead of time—but it remains one of the reliable calendar events short sellers track.
The full IPO timeline, on one line
Common mistakes and where IPOs go wrong
- Confusing “priced at $23” with “you can buy at $23.” The $23 goes to institutions who committed on the book. Retail buys the opening print, which can be far higher (SpaceX opened north of $200 against a $135 IPO price in June 2026) or lower (Jersey Mike’s opened $21 against a $23 IPO, per CNBC).
- Assuming a big first-day pop is bullish. A large pop means the company left money on the table—capital that could have funded operations instead went to institutions who flipped the stock. Founders don’t celebrate 60% pops.
- Ignoring long-run performance. Ritter’s separate long-run data set (through 2024) shows that, on an equal-weighted basis, U.S. IPOs have underperformed the broader market over three-year horizons in most years since 1980. The pop is real; the durable outperformance is not.
- Trading the lockup like a script. In big-name IPOs, everyone knows the lockup date; the supply is already priced in when the calendar hits. Aggregate float, borrow cost, and insider selling intent matter more than the calendar itself.
Recent IPO snapshot: how the concepts map to real 2026 deals
| Company (ticker) | IPO date | Offer price | Day-one open | Greenshoe / lockup |
|---|---|---|---|---|
| SpaceX (SPCX) | Jun 12, 2026 | $135 | $208 (peaked $225 by Jun 16) | Staggered lockup; ~20% released Aug 6, 2026 (~911.5m shares) |
| Jersey Mike’s (JMKE) | Jul 30, 2026 | $23 | $21 (below IPO) | 30-day / 6.52m share greenshoe (15% of 43.48m base) |
How this differs from direct listings and SPACs
Two alternative routes to a public market have become common in the last decade:
- Direct listing. The company lists existing shares on an exchange without an underwritten offering. There is no bookbuilding, no offer price, no allocation, no greenshoe, and (often) no lockup. Palantir (2020), Spotify (2018), and Coinbase (2021) used direct listings. The trade-off: no primary capital raised, and no underwriter to stabilize the first day’s trading.
- SPAC merger. A blank-check shell company (SPAC) goes public first, raises cash into trust, then merges with a private target within a set window. The target skips the S-1 process (files a merger proxy instead) and gets to publicly forecast future revenues in ways the SEC’s IPO rules restrict. SPACs surged in 2020–2021, then collapsed after regulatory scrutiny and poor post-merger performance.
The traditional underwritten IPO is still the default for large, established companies—it delivers primary capital, institutional allocation control, aftermarket stabilization, and a well-understood regulatory path.
What to learn next
- How the S&P 500 index inclusion mechanically forces buying by index funds.
- How Wall Street analyst ratings and price targets shift after a company’s first earnings post-IPO.
- Weighted average cost of capital (WACC)—the input that drives every DCF-based IPO price target.
Sources
- Jay R. Ritter, “Initial Public Offerings: Underpricing” (May 2026), Table 1 & Table 1a. site.warrington.ufl.edu/ritter/files/IPOs-Underpricing.pdf
- Jay R. Ritter, IPO Data hub. site.warrington.ufl.edu/ritter/ipo-data/
- SEC / Investor.gov, “Initial Public Offerings: Lockup Agreements.” investor.gov — IPO Lockup Agreements
- Securities Act of 1933 (governs S-1 registration). sec.gov — Securities Act
- SEC Regulation M (price stabilization rules for underwriters). sec.gov — Reg M
- FINRA Rule 2241, Research Analyst Reports (defines analyst quiet periods). finra.org — Rule 2241
- Jersey Mike’s IPO pricing (Businesswire, Jul 29, 2026). businesswire.com
- Jersey Mike’s Day-1 trading (CNBC, Jul 30, 2026). cnbc.com
- SpaceX lockup expiration coverage (The Motley Fool, Aug 5, 2026). fool.com
- SpaceX lockup coverage (Axios, Jul 17, 2026). axios.com
Disclosure: This article is for informational purposes only and is not investment advice.