The IPO Radar

Form 424B4 is the final prospectus, filed with the SEC after an offering has been priced. It is the same document as the preliminary prospectus in structure, but with one crucial difference: the numbers are real. Where the preliminary prospectus carried an indicative price range and an estimated share count, the 424B4 carries the price investors actually paid, the shares actually sold, the fees actually charged, and the proceeds the company actually receives.

If the S-1 is the document that describes what a company hopes to do, the 424B4 is the document that records what it did.

What is fixed in a 424B4 that wasn't fixed an hour earlier?

This is the useful way to think about the form. Pricing happens in the evening after the market closes. By the time the 424B4 is filed, the following have moved from estimate to fact:

Item	Before pricing	In the 424B4
Offer price	An indicative range, e.g. $26–30	A single number, e.g. $29
Shares offered	An estimate, revisable	The final count
Split between issuer and selling stockholders	Indicative	Final
Underwriting discount	A percentage assumption	A stated per-share and aggregate amount
Net proceeds to the company	Estimated at the range midpoint	Calculated from the actual price
Over-allotment option	Described	Sized against the final deal
Dilution per share	Calculated at the midpoint	Calculated at the real price
Capitalisation as adjusted	At the midpoint	At the real price
Ticker symbol	Usually stated	Confirmed

Everything else — the business description, risk factors, MD&A, management, related party transactions — is substantially unchanged. The 424B4 is the preliminary prospectus with the blanks filled in and the red-ink legend removed.

Why is it called 424B4?

Rule 424 of the Securities Act governs the filing of prospectuses, and paragraph (b) covers prospectuses filed after effectiveness. The number that follows identifies which category of filing it is:

Form	Used when
424B1	A prospectus containing information omitted from the effective registration statement, filed under Rule 430A
424B2	A prospectus for a delayed or continuous offering with price and other terms
424B3	A prospectus containing substantive changes from or additions to a previously filed prospectus
424B4	A prospectus filed under both Rule 430A and Rule 424(b)(3) — the standard form for a priced IPO
424B5	A prospectus supplement for a shelf takedown

For most IPOs you will be looking at a 424B4. Some deals use 424B1. The distinction is procedural and rarely changes what you need to read.

What should you look at first in a 424B4?

The cover page, and specifically the three-column table. It appears in every one, and it is the whole economics of the offering in about eight lines:

                              Per share        Total
Initial public offering price   $29.00      $6,264,999,978
Underwriting discount            $X.XX          $XX,XXX,XXX
Proceeds, before expenses,
  to the company                 $XX.XX      $XXX,XXX,XXX
Proceeds, before expenses,
  to the selling stockholders    $XX.XX      $XXX,XXX,XXX

That table tells you the price, the total raised, what the banks were paid, and — most importantly — how the money splits between the company and the people selling their existing shares. A deal that looks like a large capital raise in headlines is sometimes mostly an exit for existing holders, and this is where you find out.

Then look for:

The over-allotment option, on the cover and in the underwriting section. Typically up to 15% of the base offering — FINRA Rule 5110 treats anything larger as an unreasonable underwriting term — and typically exercisable for 30 days under the terms stated in the prospectus. See Greenshoe option.

The lock-up, in the underwriting section. Duration, who is bound, any staggered release, any price-based early trigger. See IPO lock-up period.

Use of proceeds, which now carries the real number and states plainly that the company receives nothing from shares sold by selling stockholders.

Dilution, recalculated at the actual price.

What does the 424B4 tell you that the S-1 couldn't?

Three things, and all of them are about what the market decided rather than what the company hoped.

Where the price landed relative to the range. Above the range means demand exceeded expectations. Below means it didn't. At the midpoint means the bankers read it about right. This single fact is one of the better available signals about how a deal was received, and it is knowable before the stock trades.

Whether the deal was upsized or cut. Compare the final share count to the last S-1/A. Medline's December 2025 offering launched marketing 179 million shares at $26–30 and priced an upsized 216 million shares at $29, raising roughly $6.26 billion — the largest global IPO of that year.

What the underwriters actually charged. The gross spread as a percentage falls sharply with deal size, and the 424B4 is where you can compute it exactly rather than assume the conventional figure. See How much does an IPO cost?.

When is a 424B4 filed?

Within two business days of pricing under Rule 424(b), and in practice almost always the morning of or the morning after pricing — before or around the time the stock begins trading.

The sequence on pricing night runs: the deal is priced after the close, the registration statement is declared effective (recorded on EDGAR as an EFFECT notice), the underwriting agreement is signed, and the 424B4 is filed. Trading opens the next morning.

See The IPO filing lifecycle.

Is the 424B4 the document investors legally receive?

Yes. It is the statutory prospectus for the offering, and the version that governs. It is also the document that carries liability: Section 11 of the Securities Act imposes liability for material misstatements or omissions in the registration statement, and the prospectus is its centrepiece.

That liability is the reason the language reads the way it does. Prospectuses are not written to be readable; they're written to be defensible. Understanding that makes them considerably easier to navigate.

See Section 11 liability.

Does a 424B4 get amended?

Not in the way an S-1 does. If something material changes after the final prospectus is filed, the company files a sticker or a new prospectus under the relevant Rule 424 paragraph, or a post-effective amendment. For an IPO that has already priced and traded, this is rare.

Ongoing disclosure then moves to the Exchange Act reporting forms: 8-K for material events, 10-Q quarterly, 10-K annually.

Quick answers

Is a 424B4 the same as a prospectus? It is the final version of the prospectus. The preliminary version — the red herring — is filed as part of the S-1 or as a 424 filing with the range still indicative.

How do I find a company's 424B4? Search the company on EDGAR and filter by form type 424B4.

Why do some IPOs file 424B1 instead? A procedural difference in which rules the filing is made under. The content you care about is the same.

Does the 424B4 include the greenshoe shares in the proceeds? No. Proceeds on the cover are stated for the base offering, with the over-allotment described separately. This is why "raised $X" figures differ between sources — some include the over-allotment and some don't. We state which basis we use in our methodology.

Can the price in the 424B4 differ from what the stock opens at? Almost always, and often substantially. The offer price is set by negotiation; the opening price is set by an auction. See Offer price vs. opening price.

What is an S-1? · S-1 vs. 424B4 · What is a prospectus? · How to read an IPO prospectus · The IPO filing lifecycle · Greenshoe option

Sources

Securities Act Rule 424 and Rule 430A
Regulation S-K Item 501 — prospectus cover page requirements
FINRA Rule 5110 — underwriting terms, including over-allotment
Securities Act Section 11
Issuer final prospectuses filed on EDGAR