What Is a 424B Prospectus and Why It Matters for Float

Direct answer: Form 424B is the final prospectus filed with the SEC by a company selling shares to the public (IPO, secondary offering, ATM). It contains the exact number of shares sold, the final price, and the closing date. These three data points let you calculate real dilution and the new float. Data aggregators read the 424B to update their numbers, often with a lag of several days.

What Exactly Is a 424B

The 424B is an SEC form that records the final prospectus of a public stock offering. When a company sells shares to the public—IPO, secondary, follow-on, ATM program, PIPE—it must first file a preliminary prospectus (S-1 or S-3). Once the deal is finalized, it publishes the definitive prospectus as a 424B.

The difference comes down to one line: the preliminary speaks in future tense ("we plan to sell approximately 5 million shares at $8 to $10"), the 424B speaks in past tense ("we sold 5,500,000 shares at $9.20 on October 24, 2026"). It's the document that officially records the transaction.

Every 424B contains:

• The exact number of shares sold (base offering + greenshoe exercised, if any)
• The public price per share
• The closing date (settlement date)
• The planned use of proceeds
• The deal structure: who's selling (the company, existing shareholders, or both), who's buying, and underwriter commissions

For a small-cap that gaps after a dilutive offering, these first three numbers make all the difference. They let you calculate how many new shares enter circulation and at what price the money enters the company.

Why "B" and the Variants (424B3, 424B4, 424B5)

The "B" refers to Rule 424(b) of the Securities Act, which governs the filing of the final prospectus. The numbers that follow correspond to sub-rules based on the type of offering and the base prospectus used.

424B2: final prospectus for a shelf offering registered under an S-3ASR (Automatic Shelf Registration). Used by large caps with continuous market access.

424B3: post-effective or supplemental prospectus, often for warrants or conversions.

424B4: final prospectus for an offering registered under an S-1. Typically an IPO.

424B5: final prospectus for a shelf offering under a standard S-3 (follow-on, ATM). Very common for micro-caps raising capital every six months.

For small-caps, you'll mostly see 424B4 (IPO or major offering with S-1) and 424B5 (quick secondary under S-3). In every case, the role is identical: officially record the final offering and its definitive terms.

Where to Find a 424B and What to Read

424Bs are public and free on EDGAR, the SEC's filing database:

1. Go to sec.gov/edgar/searchedgar/companysearch
2. Enter the ticker or company name
3. Search for "424B" in the Filings column (or use the "Prospectuses" filter)
4. Open the most recent document (HTML or PDF)

A 424B often runs 100 to 300 pages. The critical info fits on one or two pages, usually in the opening sections:

424B Section	What to Read
Offering Summary (start)	Share count, price, gross proceeds, net proceeds, greenshoe
Use of Proceeds	What the money's for (often "working capital")
Dilution (if present)	Table showing dilution to existing shareholders
Capitalization	Before/after table (shares outstanding, float)
Principal Stockholders	Who owns what post-offering (to spot the lock-up)

To measure the impact on float, you need three numbers:

1. Number of shares sold (e.g., 5,500,000)
2. Of those, how many are new shares vs. shares sold by existing shareholders ("primary" vs. "secondary"). Only primary shares dilute.
3. Float before the offering (not always in the 424B; cross-reference with the latest 10-Q/10-K or prior S-1)

New float = old float + primary shares sold. If the offering was 100% primary and the company sold 5.5 million shares, the float rises by 5.5 million on the closing date. Not the day Yahoo Finance updates its page.

Why It Matters for a Small-Cap (Massive Dilution and Aggregator Lag)

Small-caps (market cap < $300M, often < $100M) raise money frequently. They burn cash and don't have access to traditional bank credit. A pre-revenue micro-cap biotech can file 3, 5, or 10 forms 424B in a year—each time, dilution of 20%, 40%, sometimes 100% of the existing float.

Typical example: a company has 10 million shares in the float. It files a 424B5 to sell 8 million new shares at $2.50. The day after closing, the real float is 18 million. Yahoo Finance, MarketWatch, and retail brokers still show "10.00M" for 2 to 5 days. Short sellers checking EDGAR that morning see the real number. Retail traders relying on aggregators trade on stale data.

This lag is exactly what FloatVerify displays in amber ("source split"): when the SEC says 18M (read from the 424B) and the aggregator still says 10M, both numbers are shown with their date and source. No "single falsely certain figure."

The 424B also reveals hidden dilutive clauses not yet counted in the float:

• Warrants issued to underwriters or investors (future exercise, but already committed)
• Additional purchase options (15% greenshoe, which can be exercised within 30 days)
• Future debt-to-equity conversions (if the offering repays a convertible PIPE but creates a new one)

Reading the 424B means seeing dilution before it appears in short interest ratios or valuation calculations. It's the primary source, dated to the day.

The Link to Other SEC Filings (S-1, S-3, 8-K)

The 424B never stands alone. It fits into a sequence of filings that tells the full story of the offering:

1. S-1 or S-3: preliminary prospectus ("we plan to raise approximately $X million")
2. Amendments (S-1/A, S-3/A): updates to price range, share count, financials if a quarter passes
3. 424B: final prospectus ("we raised exactly $Y million, at this price, on this date")
4. 8-K (item 8.01): often filed the same day, announcing the closing (press release attached)

To track an offering in real time: the S-1 tells you it's coming (you have a few weeks to prepare), the 424B tells you it's done (you have the exact number the next day), the 8-K confirms and sometimes adds details (use of proceeds, debt repaid).

If you only read one document, read the 424B. It's the one that changes the float.

Recap

Point	Takeaway
What it is	Final SEC prospectus of a public offering (IPO, follow-on, ATM)—the document that records the sale
When filed	No later than the next business day after the first sale (often same evening)
Critical info	Number of shares sold, price, closing date, primary/secondary structure
Float impact	Primary shares increase the float on the closing date, before aggregators update
Where to read it	EDGAR (sec.gov), search for "424B" in the company's filings
Common variants	424B4 (IPO), 424B5 (secondary under S-3), 424B3 (warrants/conversions)

FAQ

What's the difference between a 424B and an S-1?

The S-1 is the preliminary prospectus, filed before the offering, with a price range. The 424B is the final prospectus, filed just before or after closing, with the actual price and exact share count. The S-1 says "we may sell 5 to 6 million shares at $8-10," the 424B says "we sold 5.5 million at $9.20 yesterday."

Where do I find a 424B on EDGAR?

On the company's EDGAR page (sec.gov/cgi-bin/browse-edgar), search for "424B" in the Filings column. The 424B3, 424B4, and 424B5 are common variants. The most recent appears at the top. Open the HTML or PDF document to read the full prospectus.

Why does the 424B change the float?

Because it officially records the creation and sale of new shares to the public. If the company sells 10 million shares in a 424B, the float increases by 10 million on the closing date—before data aggregators even update. It's the primary source of dilution.

Is a 424B always for an IPO?

No. An IPO uses a 424B, but so do secondary offerings (post-IPO): follow-ons, PIPEs going public, ATM programs, warrants exercised in bulk. Any registered public sale produces a 424B. A small-cap can file 5 or 10 forms 424B in a year.

How long after the offering does the 424B appear?

The 424B must be filed no later than the next business day after the first sale. In practice, it often appears the same evening or the next morning. If the offering closes Tuesday night, the 424B is on EDGAR Wednesday morning—well before Yahoo Finance or Finviz updates the float.

Sources

• SEC EDGAR — Company Filings Search
• Rule 424(b), Securities Act of 1933 (17 CFR § 230.424)
• SEC Forms: S-1 (Registration Statement), S-3 (Shelf Registration), 424B (Final Prospectus)
• SEC Investor Publications: "How to Read a Prospectus"

See the float, sourced and dated, on FloatVerify.

---

FloatVerify shows the float, dilution and cash burn of US small-caps, every number sourced and dated — and surfaces divergences between sources ("source split") instead of one falsely certain figure.

Disclaimer: FloatVerify is a data tool, not an investment advisory service. Nothing here is a recommendation to buy or sell. Data, not advice.