TL;DR. A US initial public offering (IPO) is the process by which a private company sells stock to the public for the first time. The mechanics are surprisingly precise: file a registration statement (Form S-1) with the SEC, market it on a roadshow during the quiet period, build a book of demand with underwriters, price the deal the night before listing, allocate shares to investors, and let the underwriters stabilize trading with a greenshoe overallotment option of up to 15% of the base deal. The whole thing typically takes 4–6 months from kickoff to ticker.
Why companies go public in the first place
Going public is a capital-raising event and a liquidity event. The company sells primary shares to raise cash for the business; existing investors and employees can sell secondary shares to monetize what they own. In exchange, the company picks up a public-market valuation, a tradeable currency for acquisitions and stock-based compensation, and a long list of new disclosure obligations.
It is not the only way to get there. A traditional IPO sells new shares through an underwriter at a negotiated price. A direct listing floats existing shares onto an exchange with no new capital raised and no underwriter syndicate. A SPAC takes a private company public by merging it with a pre-listed shell. This piece is about the traditional, bookbuilt IPO — still the dominant path for companies raising real money.
Step 1 — Pick underwriters and draft the S-1
The company starts by selecting a syndicate of investment banks. One or two are designated lead-left bookrunners (their names appear on the upper-left of the prospectus cover) and run the process; the rest are co-managers who help distribute the deal and write sell-side research after the quiet period ends.
The legal centerpiece is the registration statement. For a US-domiciled company that is a registration on Form S-1, which is the long-form prospectus required under the Securities Act of 1933. The S-1 must include audited financials, risk factors, management’s discussion and analysis (MD&A), executive compensation, related-party transactions, the use-of-proceeds, and the offering structure. Companies that qualify as Emerging Growth Companies (EGCs) under the JOBS Act — originally those with less than $1 billion in annual gross revenues, a threshold the SEC indexes for inflation — can file confidentially first, then flip it public closer to launch.
Step 2 — SEC review and the roadshow
Once filed, the S-1 enters SEC Staff review. The staff sends comment letters; the company files amendments. This back-and-forth typically takes two to three months. During this window the company is in the quiet period — the SEC reads “offer” broadly, so promotional communications about the offering are restricted. Slipping up here is called gun-jumping.
When the S-1 is close to clearable, the underwriters print a preliminary prospectus (the “red herring,” named for the red disclaimer on the cover) and the company hits the road. The roadshow is one to two weeks of back-to-back meetings with institutional investors — mutual funds, hedge funds, sovereign wealth funds, large pensions — who decide how much demand they will indicate at what price.
Step 3 — Bookbuilding and pricing
While the roadshow runs, the bookrunner builds the book: a running tally of who wants how many shares at what price. Investors submit indications of interest that look like “500,000 shares at any price up to $24” or “200,000 shares at the strike” (i.e. at whatever the final offer price is).
The night before listing, the company and the lead underwriter sit in a pricing meeting and set the final offer price and final share count. If the book is heavily oversubscribed and the indications are dense above the file range, the deal prices above the range (or even above the high end). If the book is thin or quality is poor, the deal prices below the range — or gets pulled.
A worked example: a company files a $28–$32 range on 20 million primary shares. The book is three-times covered at $34 with strong long-only demand. The lead prices the deal at $34, raising $680 million. Underwriters earn a gross spread (their fee, expressed as a percentage of proceeds) that historically clusters around 7% on small and mid-cap deals and falls sharply for mega-deals — a pattern documented by University of Florida finance professor Jay Ritter in his long-running IPO data series.
Step 4 — Allocation and the first trade
IPOs are nearly always oversubscribed, so the lead has to allocate. Allocations favor long-only institutional investors who built positions through the roadshow, anchor orders that signaled early, and — to a smaller extent — the underwriters’ best retail clients. Hot deals leave most retail accounts shut out entirely.
The next morning, the stock opens on its listing exchange (NYSE or Nasdaq). On NYSE, a Designated Market Maker runs a manual opening auction to discover the first print; on Nasdaq, the IPO Cross algorithm does it electronically. If the offer was priced at $34 and the open prints at $44, the company “left $10 a share on the table” — the difference between what the company received and what the market would have paid that morning. Across more than 9,300 US IPOs from 1980 through 2025, the mean first-day return was 19.0%, per Ritter’s underpricing dataset.
Step 5 — The greenshoe and price stabilization
The greenshoe, formally the overallotment option, lets the underwriters buy up to 15% of additional shares at the offer price. It is the single most misunderstood part of an IPO.
Here is how it works mechanically: the underwriters sell more shares than the base deal at pricing — they go short the extra 15%. Once trading opens, they have two paths to cover that short:
- If the stock trades above the offer price, they exercise the greenshoe and buy the extra shares from the company at the offer price. The company raises more capital; the underwriters earn their spread on the larger deal.
- If the stock trades below the offer price, they buy the extra shares in the open market instead — supporting the price on the way down. This is the stabilization mechanism, governed by the SEC’s Regulation M.
The name has nothing to do with the color: the option is named after Green Shoe Manufacturing (later Stride Rite), the first US company to grant one. The 15% cap is industry standard but not statutory; Regulation M imposes the disclosure and conduct rules around how stabilization can be performed.
After the bell: lock-ups and post-IPO quiet
Two things constrain what happens for the next several months:
- The lock-up period, contractually imposed by the underwriters, typically prevents insiders and pre-IPO investors from selling their shares for 90 to 180 days after listing. Lock-up expiry is itself a tradeable event — stocks often weaken into it.
- A post-effective quiet period during which the underwriters’ research analysts cannot publish ratings or price targets. The SEC and FINRA rules around analyst communications limit when the syndicate banks can initiate coverage.
The numbers: what first-day returns and fees actually look like
The next two visuals turn the abstract into something you can see. The table shows how violently first-day pop and IPO volume swing across the cycle — you do not want to extrapolate one year’s environment to the next. The chart shows the famous “seven-percent solution”: mid-sized deals cluster at exactly a 7% underwriter spread; spreads fall sharply once you cross into mega-deal territory.
| Year | Number of IPOs | Mean 1st-day return | Aggregate proceeds |
|---|---|---|---|
| 2019 | 113 | 23.5% | $39.3 B |
| 2020 | 165 | 41.6% | $61.9 B |
| 2021 | 311 | 32.1% | $119.4 B |
| 2022 | 38 | 48.9% | $7.0 B |
| 2023 | 54 | 11.9% | $11.9 B |
| 2024 | 72 | 15.3% | $20.5 B |
| 2025 | 90 | 29.3% | $39.0 B |
| 1980–2025 (all) | 9,343 | 19.0% | $1,190 B |
The process at a glance
Common misconceptions, briefly
- “First-day pop = money for the company.” No — the company is paid the offer price the night before listing. A 30% first-day pop benefits the investors who got allocations, not the issuer.
- “The greenshoe is just a fee.” It is a real short position the underwriters take, used to stabilize the stock if it breaks issue. The mechanics matter.
- “Big deal = big spread for the bank.” Inverse: the biggest deals carry the smallest percentage spreads. Visa (2008) paid 2.8%, GM (2010) paid 0.75%, Facebook (2012) paid 1.1%, Uber (2019) paid 1.3%, per Ritter’s underwriting series.
- “An IPO sets the right price.” The 19.0% historical mean first-day return suggests the issuer leaves real money on the table on average. Whether that is unavoidable adverse selection or a transfer to underwriter clients is one of the oldest debates in finance.
What to read next
- Stock Buybacks Explained — Mechanics, EPS Math, Taxes
- Enterprise Value Explained — When EV/EBITDA Beats P/E
- Leveraged Buyouts 101 — How LBOs Actually Work
Sources
- SEC, Form S-1 (registration under the Securities Act of 1933)
- SEC investor.gov — Initial Public Offering (IPO) glossary
- SEC investor.gov — Quiet Period glossary
- 17 CFR Part 242 — Regulation M (governing stabilization and overallotment)
- Jay R. Ritter, IPO Data, University of Florida — underpricing and underwriting datasets
- Greenshoe / overallotment option — history and mechanics
- Lock-up period — typical duration (90–180 days)
- Jumpstart Our Business Startups (JOBS) Act — EGC definition
Disclosure: This article was produced with AI assistance and reviewed before publication. It is for informational purposes only and is not investment advice.