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What is an S-1 filing?

An S-1 is the registration statement under the Securities Act of 1933 that a company files with the SEC to register securities for public sale — most commonly the IPO prospectus.

Last updated: 2026-05-01. Source: SEC EDGAR.

An S-1 is the IPO registration statement

Before a U.S. company can sell securities to the public, Section 5 of the Securities Act of 1933 requires the company to register those securities with the SEC. Form S-1 is the standard registration form for first-time public offerings (foreign private issuers use F-1 instead).

The S-1 is filed before the IPO prices. It is amended one or more times (each as an S-1/A) as the SEC reviews the filing, until the company and underwriters are ready to price and the SEC declares the registration effective.

What's inside an S-1

S-1s are unusually thorough — often 200-400 pages. The most-read sections in order:

Prospectus Summary: the company's elevator pitch in SEC-disclosure language.
Risk Factors: often the densest section. The company discloses every material risk to its business — competitive, regulatory, operational, financial.
Use of Proceeds: what the company plans to do with the IPO money.
Capitalization: pre-IPO and pro-forma post-IPO capital structure.
Dilution: the difference between IPO price and net tangible book value per share.
MD&A + Business + Financial Statements: same content categories as the 10-K, often more granular for smaller pre-IPO companies.
Principal Stockholders: pre-IPO ownership table — founders, VC firms, pre-IPO investors. Shows who is selling and who is holding through the IPO.
Underwriting: fees, lock-up provisions, greenshoe option mechanics.

S-1 vs. S-1/A — the IPO timeline

First S-1 filing: often heavily redacted. Estimated price range, share count, and certain agreements may still be blank.
SEC comment letters: the SEC asks questions, requests revisions, and pushes back on disclosure. Eventually published in EDGAR after effectiveness.
S-1/A amendments: each round of revisions creates an S-1/A.
Pricing amendment: shortly before IPO, the company files an S-1/A with the price range.
Final prospectus (424B): after pricing, a 424B prospectus locks the actual price and share count.
Effectiveness + trading: SEC declares the registration effective; shares begin trading.

S-1 vs. S-3 vs. F-1

S-1: first-time U.S. domestic registration. Heaviest disclosure.
S-3: shelf registration for already-public seasoned issuers. Much shorter — incorporates the 10-K and 10-Q by reference.
F-1: equivalent of S-1 for foreign private issuers (e.g., a Chinese or European company listing in the U.S.).

S-1/A — amendments

SecFilingDex tracks 12 S-1/A amendments alongside the originals. Reading consecutive S-1/A versions against each other is the cleanest way to see what the SEC pushed back on — language that disappears or grows between amendments is signal.

Our view

The S-1 is the most honest document a company will ever file. Risk factors are written when the company most needs to be candid, before public pressure shapes management language. Read the S-1 — and especially the early S-1 vs. final S-1/A diff — for any IPO you're seriously evaluating. The disclosure quality compresses sharply once the company is public.

See live data

Browse live S-1 filings — 9 filings indexed. Updated as new EDGAR submissions are ingested.

Glossary

S-1: Registration statement under the Securities Act of 1933, Form S-1. The form U.S. domestic issuers file to register securities for public sale, most commonly used for IPOs.
S-1/A: An amendment to a previously filed S-1. Filed during the SEC review and pricing process; a typical IPO sees several S-1/A filings before effectiveness.
Effectiveness: The SEC's declaration that a registration statement is effective. After effectiveness, the issuer may sell the registered securities.
Lock-up period: Contractual restriction prohibiting pre-IPO holders (founders, employees, early investors) from selling shares for a defined period (typically 90-180 days) after the IPO. Disclosed in the S-1 underwriting section.
424B prospectus: Final prospectus filed under Rule 424(b) after the registration statement becomes effective and pricing is complete. Contains the locked-in offering price and share count.