S-1 vs. 424B4: What Actually Changes
The S-1 is the registration statement a company files to go public. The 424B4 is the final prospectus filed after the offering is priced. They are largely the same document — the same business description, the same risk factors, the same audited financials. What changes is everything that depends on the market: the price, the size, the split between the company and its selling shareholders, and the fees.
Reading the two side by side takes about ten minutes and tells you more about how a deal was received than most of the coverage written about it.
The short version
| S-1 (and S-1/A) | 424B4 | |
|---|---|---|
| When filed | Before pricing, often months before | Within two business days of pricing |
| Purpose | Register the securities; open SEC review | Deliver the final terms to investors |
| Offer price | Absent, then an indicative range | A single final number |
| Share count | Estimated, revisable | Final |
| Proceeds | Estimated at the range midpoint | Actual, at the real price |
| Underwriting discount | Described, often as a placeholder | Stated per share and in aggregate |
| Cover legend | Red-ink "subject to completion" language | Removed |
| Amended? | Yes, repeatedly, as S-1/A | Rarely |
| Legal status | Registration statement under review | The statutory prospectus that governs |
What changes, line by line
The cover page
This is where nearly all the meaningful change is concentrated.
Offer price. The S-1 as originally filed has no price at all. A later amendment adds an indicative range. The 424B4 replaces the range with one number.
Shares offered. An estimate in the amendments, final in the 424B4. Deals get upsized when demand is strong and cut when it isn't.
The three-column table. The S-1 shows price, underwriting discount, and proceeds with placeholders or midpoint estimates. The 424B4 shows real numbers for each, broken out between proceeds to the company and proceeds to selling stockholders.
Selling stockholder participation. Sometimes this changes materially between the last amendment and pricing — existing holders decide to sell more or fewer shares depending on the price.
The red-ink legend. The preliminary prospectus carries the "subject to completion" language, printed traditionally in red ink, which is where the nickname "red herring" comes from. It's gone in the final. See Red herring prospectus.
Ticker and exchange. Usually stated in the amendments, confirmed in the final.
Use of proceeds
The section recalculates against the real price. Watch for whether the stated uses changed in substance or only in amount. A company that said it would use proceeds for general corporate purposes in the S-1 and still says so in the 424B4 has told you nothing either time.
Capitalisation and dilution
Both sections are calculated from the offer price. In the S-1/A they assume the midpoint of the range; in the 424B4 they use the actual price. If the deal priced well above the range, dilution per share looks materially different in the final.
Underwriting
The syndicate list is usually settled by the later amendments. What firms up in the 424B4: the per-share underwriting discount, the aggregate discount, the exact over-allotment share count, and any final changes to lock-up terms.
Everything else
Business, risk factors, MD&A, management, compensation, related party transactions, description of capital stock. These are substantially identical between the last amendment and the final. If something changed here, it's worth a close look, because it means something surfaced late.
What does each change tell you?
Priced above the range. Demand exceeded what the bankers modelled when they set it. Often, though not always, followed by a strong debut.
Priced below the range. Demand didn't materialise at the indicated level. The company chose to proceed anyway rather than pull the deal.
Priced within the range. The most common outcome and the least informative.
Deal upsized. The book was covered deep enough that the company and selling holders chose to sell more. Medline's December 2025 offering launched marketing 179 million shares at $26–30 and priced 216 million at $29, raising roughly $6.26 billion.
Deal downsized. Demand supported the price but not the volume, or the company preferred a smaller float.
Secondary component grew. Existing holders took the opportunity to sell more than originally planned. Worth noting, though not automatically a negative signal — it's often a mechanical consequence of upsizing.
Range revised before pricing. Visible in the amendments rather than the 424B4, and the single best real-time indicator of how a live deal is going.
A worked comparison
Which one should you read?
Reading about a company you might invest in: the 424B4, because it's final and it's what governs.
Following a live deal: the S-1 and its amendments, because that's where the story is still developing and where range revisions appear.
Researching a company's history: the original S-1, because it's the least polished account of what the business looked like before it had public investors to manage.
Comparing across many deals: the 424B4, because the fields are consistent and final, which is why it's the basis for most structured IPO data, including ours. See Methodology.
Quick answers
Is the 424B4 just the S-1 with the price filled in? Substantially, yes — plus recalculated capitalisation and dilution, and the removal of the preliminary legend.
Do all IPOs file a 424B4? Most do. Some file a 424B1 instead, which is a procedural difference in which rules the filing is made under.
Why does the S-1 exist if the 424B4 is the operative document? Because the registration statement is what gets filed, reviewed, amended, and declared effective. The final prospectus is the output of that process, not a substitute for it.
How many S-1/A amendments are typical? Several. The count varies with the complexity of the business and how much the SEC pushes back.
Can I see what the SEC objected to? Yes. Comment letters and company responses become public on EDGAR after the fact.
Where do I find both? EDGAR, filtering by form type. DRS and DRS/A for the confidential drafts, S-1 and S-1/A for the public registration statement, 424B4 for the final.
Related
What is an S-1? · What is Form 424B4? · Red herring prospectus · How to read an IPO prospectus · The IPO filing lifecycle · How is an IPO priced?
Sources
- Securities Act Rules 424 and 430A
- Regulation S-K Items 501 and 504 — cover page and use of proceeds
- SEC EDGAR — filing types and public comment letter correspondence
- Issuer registration statements and final prospectuses on EDGAR